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We compared the effects of exogenous insulin and porcine ST (pST) on follicular development after weaning. Crossbred primiparous sows received saline (1.5 mL i.m.; n = 9), insulin (.4 IU/kg BW s.c.; Eli Lilly Lente Iletin II; n = 10), or pST (40 [[micro]gram]/kg BW i.m.; n = 10) from d 1 to 5 after weaning (d 0). Ovaries were collected, the diameter of each follicle [greater than or equal to] 2 mm was measured, and fluid from the 20 largest follicles was assessed for IGF-I, IGF binding proteins (IGFBP), estradiol, progesterone, and testosterone. The total number (27.7, 25.3, and 29.1 for saline, insulin, and pST, respectively; SEM = 3.2) and average diameter (4.7, 5.2, and 5.5 mm for saline, insulin, and pST treatments, respectively; SEM = .3 mm) of ovarian follicles were not affected by insulin or pST treatment. The pST and insulin increased follicular fluid estradiol and testosterone in medium and large follicles compared to fluid from saline-treated sows, but the increase was greater for insulin than for pST treatment (treatment x size interaction, P < .01). Similarly, progesterone concentrations in follicular fluid were higher in medium and large follicles after insulin treatment, and pST treatment induced higher progesterone concentrations in small follicles and increasingly lower concentrations of progesterone in medium and large follicles (treatment x size interaction, P < .0007) compared to saline treatment. Follicular fluid IGF-I was greater (treatment x health interaction, P < .0001) in atretic and nonatretic follicles from pST-treated sows than in those from insulin- and saline-treated sows. Follicular fluid IGFBP-2 (tendency, P < .07) and IGFBP, possibly representing IGFBP-5 (30 kDa) and IGFBP-4 (22 kDa), were higher in atretic follicles than in nonatretic follicles (P < .05), whereas IGFBP-3 was not influenced by health status. The 30- and 22-kDa IGFBP were also influenced by treatment, increasing due to pST compared with saline or insulin treatments (P < .008). Follicular fluid IGFBP-2 and IGFBP-3 were not influenced by treatment. In conclusion, pST and insulin positively influenced follicular steroidogenesis and possibly follicular development, although through different mechanisms. Key Words: Sows, Insulin, Estradiol, Somatotropin, Insulin-Like Growth Factor, Follicles

The objective of this study was to determine whether the improvements in growth and efficiency of gain achieved by recombinant porcine somatotropin (pST) are associated with altered expression of the p94, calpastatin, or [Alpha]-actin genes in porcine longissimus (L D) muscle. Forty-eight barrows (initial 64.2 to 67.4 kg BW) were assigned to four treatments (n = 12) arranged as a 2 x 2 factorial in a randomized complete block design. Factors were duration of treatment (3 or 6 wk) and pST administration (0 or 3 mg[center dot][pig.sup.-1][center dot][d.sup.-1]). Plasma samples were obtained 24 h after the first pST injection and at the end of the each treatment period for assays of selected variables. The LD samples were obtained at 3 and 6 wk of pST treatment. Northern blot analysis of calpastatin expression in LD muscle revealed three distinct transcription products of approximately 8.5 (CPST I), 5.5 (CPST II), and 2.5 (CPST III) kb; CPST II was reduced (P < .02) 33 and 61% by pST at 3 and 6 wk, respectively, whereas CPST I and III were not influenced (P > .12). Neither [Alpha]-actin nor p94 was responsive to pST injection. As expected, pST resulted in higher (50%, P < .02) plasma insulin within 24 h and one- and twofold higher (P < .01) concentrations at 3 and 6 wk, respectively. Glucose was increased (P < .01) at 3 (15%) and 6 (10%) wk, whereas urea nitrogen was reduced (32 to 36%, P < .01). The efficacy of pST was evident in that ADG was improved (P < .01) 11 to 13% independent of time. Likewise, feed intake was reduced (P < .01) 10 to 11% and gain: feed improved (P < .01) approximately 26% for pigs receiving pST independent of time. These data indicate that the enhanced muscle growth achieved by pST is not associated with altered expression of p94 or [Alpha]-actin, or an increase in the abundance of any calpastatin transcription product. Key Words: Muscle Tissue, Actin, Pigs, Somatotropin

We investigated the effects of recombinant porcine somatotropin (pST) on the requirement for P to maximize lean tissue accretion and to minimize fat tissue accretion in two experiments using finishing pigs. Corn-soybean meal diets with varying levels of P were fed, and Ca was adjusted to maintain a Ca:P ratio of 1.1:1. In Exp. 1, 96 pigs were fed dietary P concentrations of .35, .45, and .65% from 75 to 109 kg BW. One-half of the pigs were injected daily with 4 mg of pST. Administration of pST increased (P < .05) percentages and accretion rates of lean tissue, bone, skin, water, and protein, but it reduced (P < .05) those of fat tissue and lipid. Increasing dietary P had little effect on chemical composition or accretion rates in untreated pigs, but it increased (P < .05) ash percentage and accretion in pigs treated with pST. Experiment 2 consisted of 66 pigs fed six dietary P concentrations (.35, .50, .65, .80, .95, and 1.10%) from 72 to 114 kg. One-half of the pigs were injected daily with 4 mg of pST. Percentages and accretion rates of lean tissue, bone, skin, water, and protein increased (P < .05) with pST, but those of fat tissue and lipid were reduced (P < .05). Increasing dietary P increased accretion rates of bone and skin (linear, P < .05), lean tissue, water, protein, and ash (quadratic, P < .05), and it reduced (quadratic, P < .05) that of lipid in pigs treated with pST. Dietary P level did not consistently affect percentages or accretion rates of tissues or chemical components in untreated pigs. In most instances, pigs treated with pST required higher dietary P levels and greater daily intakes of P to maximize lean tissue and protein deposition and to minimize fat tissue and lipid accretion than untreated pigs. These results indicate that finishing pigs treated with pST require higher dietary percentages of P to maximize carcass lean deposition as compared with untreated pigs. Key Words: Pigs, Somatotropin, Phosphorus, Muscles, Fat

We conducted two experiments to evaluate the effects of recombinant porcine somatotropin (pST) on the P requirement of finishing pigs. Corn-soybean meal diets with varying levels of P were fed, and Ca was adjusted to maintain a Ca:P ratio of 1.1:1. In Exp. 1, 96 pigs were fed dietary P concentrations of .35, .45, and .65% from 75 to 109 kg BW. One-half of the pigs were injected daily with 4 mg of pST. Pigs treated with pST consumed less feed and gained more efficiently than untreated pigs (P < .01). Increasing the dietary P level produced linear (P < .05) improvements in most metacarpal-metatarsal (MM) and femur traits. Administration of pST increased (P < .02) bone weight, but it reduced (P < .03) bone strength and the percentage of ash. The increases in percentage of ash and ash accretion associated with increasing dietary P were more pronounced in pST-treated pigs than in untreated pigs (pST x P, P < .01). Experiment 2 consisted of 66 pigs fed six dietary P concentrations (.35, .50, .65, .80, .95, and 1.10%) from 72 to 114 kg. One-half of the pigs were injected daily with 4 mg of pST. Pigs treated with pST gained faster and more efficiently (P Key Words: Pigs, Somatotropin, Phosphorus, Bone Mineralization

We conducted two experiments to determine the efficacy of exogenous porcine somatotropin (pST) on enhancing performance during an early phase of growth (10 kg initial BW) when pigs are already growing efficiently and have high rates of lean deposition and low rates of lipid deposition. In Exp. 1, performance was measured on 45 barrows that received one of five daily doses (0, 50, 100, 150 and 200 [[micro]gram]/kg BW) of recombinant pST. In Exp. 2, 27 barrows were used in a slaughter-balance study in which two groups received daily either buffer (control) or 120 [[micro]gram]/kg BW of pST and the third group was slaughtered for initial body composition. In both experiments, pigs received daily i.m. injections of their respective dose for 20 d. The diet was fed for ad libitum consumption and calculated to contain 3.5 Mcal DE/kg, 22.3% CP, and 1.5% lysine. Administration of pST failed to alter overall growth rate or efficiency of gain in either experiment. However, in Exp. 2 pigs treated with pST had increased deposition rates of protein and water but reduced lipid deposition rates. Furthermore, pST treatment resulted in characteristic reductions in plasma urea nitrogen and elevations in glucose and NEFA. Plasma concentrations of insulin and IGF-I were also increased, but pST reduced IGF-II and IGF binding protein-2. Overall, the data demonstrated that very young pigs respond to pST with enhanced lean tissue accretion and metabolic changes, but the response is attenuated compared with previous studies in older growing pigs. Key Words: Pigs, Somatotropin, Chemical Composition, Growth, Insulin-Like Growth Factor

Four experiments were conducted to elucidate the effects of porcine somatotropin (pST, growth hormone) on circulating testosterone concentrations in boars. In Exp. 1, jugular-cannulated obese boars were administered 4 mg recombinant (r) pST/d for 24 d before collection of samples at 15-min intervals over 6 h for measurement of pST, testosterone, and LH. Somatotropin treatment decreased plasma concentrations of testosterone and LH (P < .05). In Exp. 2, White composite boars were administered rpST with imp]ants (4 mg/d) for 10 to 28, 16 to 28, or 22 to 28 wk of age. Reductions in testosterone concentrations were proportional to the length of time rpST was administered; boars treated for 18 wk had the lowest testosterone concentrations. Concentrations of LH declined throughout the study in rpST-implanted boars but remained static in untreated, control boars. In vitro production of testosterone and dehydroepiandrosterone/dehydroepiandrosterone sulfate was unaffected by rpST treatment, and hCG stimulation of in vitro androgen secretion was similar in rpST and control treatments. In Exp. 3, i.v. injection of pituitary pST (USDA-B1; 5 [[micro]gram]/kg BW) into jugular-cannulated White composite and Meishan boars resulted in an acute increase in circulating LH followed by an increase in testosterone concentrations, which then declined to below preinjection levels at 6 to 7 h after pST injection. Multiple injections, two or four per day, of 5 [[micro]gram] pST/kg BW resulted in decreased testosterone concentrations in White composite boars, whereas in Meishan boars testosterone concentrations were unaffected (Exp. 4). Concentrations of LH were not different from control values in either breed, but in both breeds, four injections of pST per day produced lower LH concentrations than did two injections per day (P < .01). Depression of circulating concentrations of androgens in boars requires extended periods of pST treatment. Key Words: Pigs, Somatotropin, Testosterone, Testes

We hypothesized that much of the positive effect of porcine somatotropin (pST) on the immune system would be offset by the pST/IGF stimulation of gonadal function and that there would be negative effects on thymic weight and function from increased androgens in males. Male and female hogs (78 boars, 90 gilts) representing three genetic lines (lean, obese, and crossbred meat type) received 0, 2, or 4 mg of recombinant pST/d via implant for 42 d. Blood samples were collected on 0, 7, 14, 28, and 42 d of the trial for changes in pST, IGF-I, IGF-II, thymosin [Beta]4, dehydroepiandrosterone/dehydroepiandrosterone sulfate (DHEA/DHEAS[O.sub.4]), and testosterone concentrations. Thymic, splenic, gonadal, and adrenal weights were collected at slaughter (d 42). Thymic weights increased with dose of pST in both sexes (P < .01), but splenic weights were unaltered. Adrenal weights increased with dose of pST (P < .01), but gonadal weights showed no response to pST in either sex or any line. Overall, concentrations of pST, IGF, and thymosin [Beta]4 increased with dose of pST. Serum testosterone concentrations in boars declined with dose of pST in lean and obese lines, and DHEA/ DHEAS[O.sub.4] declined in all lines with pST treatment. Testicular testosterone concentrations were not different among lines or doses of pST, indicating no stimulatory effect of increased pST/IGF-I on Leydig cell function. Although pST and its effects through increased circulating IGF are thought to be overall stimulants of growth and protein accretion, the actions on the tissues of the immune system (thymus/spleen) and steroidogenic tissues (adrenal/gonadal) can be selective. Increases in thymic weights and thymosin [Beta]4 concentrations from pST treatment in boars were partially due to the pST-induced decline in circulatory androgens, and the responses found in this in vivo model do not support pST/IGF effects documented in in vitro systems on Leydig cell function. Key Words: Pigs, Thymus, Testes, Testosterone, Thymosin

To determine the effect of exogenous porcine somatotropin (ST) on lactation performance of sows, 24 first-litter sows were injected daily at 0800 with either 10 mg of recombinant ST or an equivalent volume of buffer between d 8 and 39 of lactation. Litter size was standardized to six (n = 2), seven (n = 8), eight (n = 6), or 10 (n = 8) pigs within each pair of sows by fostering pigs within a few days after parturition. Milk yield and composition of sows given ST was similar at all stages of lactation to that of control sows. Combining treatment data revealed that the milk yield of sows was related linearly (P < .01) to litter size and was described with the following equation: MY = 1.03 ([+ or -].71) + .899 ([+ or -].102) LS (n = 24, [r.sup.2] = .78), where MY is average milk yield (kilograms/day) of sows over 4 to 7, 11 to 14, 18 to 21, 25 to 32, and 32 to 39 d of lactation and LS is number of pigs in the litter. The body temperature of sows increased (P < .05) in response to administration of ST. Plasma IGF-I and glucose were increased (P < .05) by ST, but plasma urea concentrations were lower (P < .05) in ST-treated sows. Sows treated with ST lost more backfat (P < .05) during lactation, but neither voluntary feed intake nor body weight loss was significantly (P > .05) affected by ST. These data indicate that a 10-mg daily injection of ST from d 8 to 39 of lactation alters metabolism but does not increase milk production in lactating first-litter sows. Key Words: Sows, Lactation, Somatotropin, Milk Production

The objective of this study was to determine the effects of recombinant porcine somatotropin (rpST) on placental size, fetal growth, and maternal and fetal IGF-I and IGF-II concentrations. Twenty-four pregnant gilts received daily injections of either 1 mL of saline (control) (n = 12) or 5 mg of rpST (n = 12) from d 30 to 43 of gestation. Gilts were slaughtered on d 44 of gestation, reproductive tracts were removed, and fetal weight and length, placental weight, and implantation length were recorded. There was no effect of rpST on fetal or implantation length. Placental weight increased with rpST administration (71.20 [+ or -] 3.52 vs 58.35 [+ or -] 3.41 g; P < .02), as did fetal weight (18.06 [+ or -] .55 vs 16.44 [+ or -] .53 g; rpST vs control, respective]y; P < .05). Implantation lengths were partitioned into quartiles to determine the effect of rpST on fetuses with different implantation lengths. The effect of rpST on fetal weight was greater in the first quartile (< 137.5 mm) than in the fourth quartile (> 240 mm) (16.04 vs 13.86 g compared with 19.47 vs 18.21 g, respectively). Analy-sis using a modified Brody curve suggests that the effect of rpST treatment on fetal weight is equivalent to the effect of increasing implantation length by 58.8 mm. Administration of rpST numerically raised IGF-I (P = .07) and IGF-II (P = .12) concentrations in fetal serum. Although maternal serum IGF-I concentrations were similar at d 30, treatment with rpST increased these concentrations over time (77.76, 247.75, 267.85 vs 82.59, 79.59, 77.97 ng/mL on d 30, 37, 43, respectively; P < .001, SE = 14.09). Maternal IGF-II concentrations were also similar at d 30 but decreased over time with rpST treatment (265.78, 219.61, 191.05 vs 285.44, 284.72, 283.05 ng/mL; P < .03, SE = 14.03). Increased maternal IGF-I concentrations may exhibit negative feedback on maternal IGF-II concentrations. The more pronounced effect of rpST on growth in fetuses with shorter implantation lengths suggests that rpST may increase uptake or utilization of nutrients by fetuses. In addition, nutrient transfer across placental membranes may be enhanced by rpST. Key Words: Somatotropin, Fetal Growth, Insulin-Like Growth Factor, Pigs

The shift in nutrient partitioning induced by porcine somatotropin (pST) is accompanied by a decrease in insulin sensitivity for whole-body glucose uptake. The relative contribution of metabolic changes in the hindlimb was investigated in eight pigs (55 kg) that had received recombinant pST (120 [[micro]gram]/kg) or excipient (control) for 7 d. Uptake of metabolites by the hindlimb was measured under basal conditions and during hyperinsulinemic-euglycemic clamps at low [14 ng/(kg[centered dot]min)] and high [360 ng/(kg[centered dot]min)] insulin infusion rates. Dextrose infusion rate required to maintain euglycemia was used as an index of whole-body glucose uptake in response to exogenous insulin. Effects of pST on hindlimb and whole-body glucose uptake were evident only at physiological levels of insulin (basal and low insulin infusion rate). During the low rate of insulin infusion, dextrose infusion rate was 79% lower for pST-treated pigs and glucose uptake by the hindlimb was 59% lower compared with control pigs. The decrease in glucose uptake by the hindlimb was entirely accounted for by the estimated reduction in glucose utilization by adipose tissue of the hindlimb. Glucose:oxygen quotients were reduced during basal (57%) and low insulin infusion (63%) with pST treatment, indicating a change in the pattern of substrate utilization. This is consistent with the concept that pST directs nutrients away from adipose and towards muscle growth by altering the response of tissues to homeostatic signals such as insulin. INDEXING KEY WORDS: swine; somatotropin; insulin; glucose; nonesterified fatty acids

A 10-wk trial was conducted with 60 barrows and 60 gilts (initial weight = 47 kg) to investigate the effect of pST treatment (3 mg/d) for wk 0 to 5, 5 to 10, or 0 to 10 on performance, carcass traits, and adipose tissue cellularity of finishing hogs. The primary objective of the study was to determine the effect of 5 wk of pST treatment followed by 5 wk of withdrawal on performance and carcass traits relative to a control or to pigs treated for the entire period. After 5 wk, pST-treated pigs exhibited improved (P [is less than] .001) gain (11%) and efficiency (22%) and decreased (P [is less than] .001) feed intake (-22%) and 10th rib backfat accretion (-93%, P [is less than] .001). There was an increase in adipose cell number/gram of tissue (control, 2.57 vs pST, 3.36 x [10.sup.6]/g; P [is less than] .005) and a decrease in cell diameter (control, 72.4 vs pST, 67.2 [micro]meter; P [is less than] .005). Backfat thickness and cell diameter increased in control pigs from wk 5 to 10. During the last 5-wk period, pST-treated animals continued to exhibit improved performance and maintained adipose cell size distribution and number similar to the pST-treated pigs at wk 5. Pigs treated for the first 5 wk and withdrawn from treatment for the second 5 wk had decreased efficiency (-12%, P [is less than] .05) and a twofold increase in backfat accretion (P [is less than] .001) relative to control. The increase in backfat thickness was accompanied by an increase in adipocyte diameter, indicative of lipid filling. Most of the benefits of pST observed during the first 5 wk were lost during the withdrawal period. Reductions in carcass fat in response to pST treatment are at least partially accounted for by inhibition of lipid filling in adipose tissue, an effect that is reversed upon cessation of treatment.

Treatment of pigs with porcine somatotropin (pST) is associated with altered nutrient partitioning. The aim of this investigation was to determine the role of pST in protein and collagen deposition in growing pigs. Barrows were treated daily with buffer or pST when they weighed between 30 and 64 kg (n = 8 pigs/group). Pigs were restrictively fed such that the average feed intake for both groups was 1.86 kg/d. Treatment with pST was associated with 25, 55, 78 and 31% higher growth rates for carcass, skin, viscera and head, respectively. Total protein depositions (g/d) were 52, 60, 81, 42 and 54% greater in carcass, skin, viscera, head and empty body, respectively, of pST-treated pigs. Collagen represented approximately 70, 15 and 43% of total protein in skin, viscera and head; pST did not influence this ratio. However, collagen relative to total protein was 16% lower in the carcass of pST-treated pigs. Deposition rate of collagen was higher in all components of empty body, except carcass, as a result of pST treatment. The ratio of non-collagen protein to collagen deposition rate was 49% greater in the carcass of pST-treated pigs. The deposition rate of acid-soluble collagen was approximately 2-fold higher in skin but was 25% lower in carcass of pST-treated pigs. Depositions of insoluble collagen in viscera and head of pST-treated pigs were 74 and 46% greater, respectively, than for controls. These data show that pST treatment enhances collagen deposition in skin, head and viscera, whereas non-collagen protein deposition and collagen maturation are enhanced in the carcass.

Daily administration of recombinant porcine somatotropin (rpST) has marked effects on growth performance of swine. Protein accretion rates are dramatically increased with rpST treatment. However, the effect of rpST on specific muscle proteins has not been addressed. The purpose of this study was to examine the effects of rpST on 1) the distribution pattern of isomyosins, 2) the total myosin heavy chain protein levels, and 3) myosin heavy chain mRNA abundance present in swine skeletal muscle. There were no differences in myosin isoform composition in the longissimus muscle resulting from porcine somatotropin treatment. There were also no differences in the myosin heavy chain protein concentration within the longissimus muscles. In accordance with the protein levels, myosin heavy chain mRNA expression was not altered with rpST treatment. This study shows that although the pig responds to rpST with increased protein accretion rates, the proportion of myosin per milligram of total protein remains constant. Myosin was not altered by type, concentration, or expression level. By combining these tools we are now able to examine a myosin on both a protein and message level throughout growth.

The present study was undertaken to determine the effects of exogenous porcine somatotropin (pST) on IGF-I gene expression in liver, skeletal muscle (longissimus dorsi), and s.c. adipose tissue of growing pigs. Twenty prepubertal gilts ( [nearly equal to] 60 kg BW) were allotted to four treatment groups (n = 5) and treated with either 0, 35, 70, or 140 [mu]g/kg BW of recombinantly derived pST by daily i.m. injection for 7 d. Serum concentrations of IGF-I were determined by RIA and IGF-I mRNA levels were determined by direct counting of individual samples on slot blots. Administration of pST increased IGF-I concentration in serum. This was accompanied by significant increases (P < .05) in IGF-I mRNA abundance in liver and s.c. adipose tissue; the effects were maximal at the lowest dose of pST. Insulin-like growth factor I mRNA levels were increased 2.5- and 4.5-fold, respectively. Levels of IGF-I mRNA were very low in longissimus muscle and were unaffected by administration of pST. When expressed as picograms of mRNA/10 [mu]g of total RNA, IGF-I mRNA levels were highest in s.c. adipose tissue. Levels of IGF-I mRNA were l.9-fold higher in s.c. adipose tissue than in liver of control animals, and pST administration increased this difference to 3.2-fold. Our results suggest that 1) the effects of pST administered by daily i.m. injection on IGF-I gene expression in pigs are tissue-specific and 2) the stimulatory effects of pST administered in this manner on muscle growth in pigs are not associated with increased expression of the IGF-I gene in skeletal muscle. Key Words: Growth, Insulin-Like Growth Factor, Somatotropin, Somatomedin

One hundred eight gilts (initial weight = 58.5 kg) were used to determine the effects of porcine somatotropin (pST) and dietary P on growth performance and bone mechanical properties and mineralization during the finishing phase (58 to 105 kg) and a 35-d postfinishing phase. Gilts were injected daily with placebo (control) or 4 mg of pST and fed diets containing .4, .8, or 1.2% P in a 2 x 3 factorial arrangement. From 58 to 105 kg, administration of pST increased (P |is less than~ .01) ADG and G/F and decreased (P |is less than~ .01) ADFI. When mean weight of the gilts in a pen reached 105 kg, half the gilts were slaughtered and first rib, femur, and third and fourth metacarpals were collected for determination of mechanical properties and bone ash. A pST x P interaction was observed (P |is less than~ .05) for rib bending moment and modulus of elasticity; maximum rib bending moment was attained by control gilts at .8% P and rib modulus of elasticity values remained constant across P levels, whereas rib bending moment and modulus of elasticity increased as dietary P increased from .4 to 1.2% in pST-treated gilts. Administration of pST decreased (P |is less than~ .05) stress of the rib, femur, and metacarpals compared with control gilts. Increasing dietary P resulted in a linear (P |is less than~ .10) increase in bending moment, stress, and ash content for rib, femur, and metacarpal bones. The remaining 54 gilts were individually fed 1.8 kg/d of a common diet for 35 d postfinishing. A pST x P interaction was observed (P |is less than~ .03) for treatment combination received in the finishing phase on rib bending moment at the end of the postfinishing phase. Control gilts had similar rib bending moment values regardless of the dietary P level fed during the finishing phase, and pST-treated gilts that received the higher dietary P in the finishing phase still had greater rib bending moment values at the end of the postfinishing phase. Gilts that received higher P levels in the finishing phase also had increased (linear, P |is less than~ .05) ash content at the end of the postfinishing phase. Gilts treated with pST and receiving the .4 or .8% P diet during the finishing phase showed a compensatory increase in bone strength to a value equal to or exceeding that of control gilts by the end of the postfinishing phase. We conclude that gilts administered pST during the finishing phase do not have greater daily requirements for Ca and P than control gilts to maximize growth performance but do have greater requirements than control gilts to attain comparable bone strength during the finishing phase.

An experiment was conducted with 24 crossbred (Landrace X Yorkshire X Duroc) finishing pigs (mean BW 85 kg) to study the effects of a single 100-mg recombinant porcine somatotropin (rpST) implant on the tissue mineral status of pigs exposed to either a thermoneutral (TN; 18 to 21 degrees C, 50 to 55% RH) or cold (C; 5 to 15 degrees C, 50 to 70% RH) environment until BW averaged 110 kg. The implants used in this study delivered an average 2.4 to 2.5 mg of rpST/d during the course of the study. Control pigs were implanted with a placebo. All diets were supplemented with minerals at levels that either met or exceeded the requirements of an 85-kg pig. At slaughter (mean BW 110 kg), tissues were collected and analyzed for selected macro- and microminerals. Pigs treated with rpST had higher (P < .05) Ca concentrations and total Ca in liver and kidney and higher (P < .05) Ca concentrations in muscle. Total P, Mg, Na, and K were all higher (P < .05) in the liver and kidneys of rpST-treated pigs. In general, rpST had little influence on Cu, Zn, and Fe in tissues. No consistent trend was evident in the response of tissue minerals to environmental temperature. Results indicated that pigs treated with rpST and supplemented with adequate minerals accumulated more minerals in certain tissues than did pigs not given rpST.

Thirty-two pigs (average weight, 74 kg) were used to determine the effects of recombinant porcine somatotropin (rpST) and dietary CP concentration on carcass and noncarcass tissues. Pigs were injected intramuscularly with either rpST (50 microns g center dot kg BW to the -1 center dot d to the -1; n = 16) or vehicle (n = 16) at 0900 for 24 d. Half the treated and control pigs were given ad libitum access to either a 14 or 20% CP corn-soybean meal diet. The left side of the carcass was physically dissected into separable skin, soft tissues, and bone. Tissue samples were obtained for enzyme assays, proximate analysis, and fatty acid profiles. Proximate analysis (fat, water, protein) of adipose tissue (AT) samples indicated that rpST decreased the percentage of ether extractable lipid (P < .01) and increased the percentage of protein and water (P < 0.5, P < .01) in intermuscular (IM), subcutaneous (SC), and intrafascicular (IF) AT depots and slightly altered fatty acid profiles of longissimus muscle IF and SC AT. Fatty acid synthesis and malic enzyme activity were decreased by rpST (P < .01), suggesting that lipogenesis was decreased; however, lipolysis was unaffected. Pigs fed the high-CP diet (20%) had decreased AT malic enzyme activity (P < .05) and fatty acid synthesis (P < .05). Additionally, pigs fed the high-CP diet had greater kidney weights (P < .01). Heart, liver, and kidney weights were heavier (P < .01) in pigs treated with rpST, whereas skin and total bone weight were unaffected. Neither weights nor lengths of four individual long bones were affected by dietary protein concentration or administration of rpST.

The pharmacokinetics of prolactin (PRL) and growth hormone (GH) are not known in neonatal pigs. In this study, six boars, ages 13 and 26 d, were used to determine metabolic clearance rate (MCR), half-life (t(sub 1/2)), and volume of distribution (Vd) of immunoreactive porcine PRL (ipPRL) and immunoreactive porcine GH (ipGH). Blood samples were collected through indwelling jugular catheters at 0, 1, 2.5, 5, 10, 15, 30, 45, and 60 min after a 20 ng/g of BW (per hormone) cocktail of porcine PRL and GH. Analysis of the ipPRL disappearance curves indicated an apparent MCR of 13.79 + or - 2.45 and 23.79 + or - 4.10 mL/min for boars at 13 and 26 d of age, respectively (P = .0008). The t(sub 1/2) of ipPRL did not differ between ages (P = .9201). The apparent MCR of ipGH at 13 and 26 d were 10.60 + or - 2.09 and 27.30 + or - 4.55 mL/min, respectively, and this difference was still evident after adjustment for BW (P = .0465). The ipGH t(sub 1/2) decreased with age (P = .0232), 21.32 + or - 2.55 vs 13.57 + or - 3.35 min for 13 and 26 d, respectively. The apparent distribution volume for ipPRL was higher than that for ipGH at both ages (P = .0021). Within each age, the apparent MCR of ipGH and ipPRL did not differ significantly. These data represent the first clearance measures reported for ipPRL and ipGH in neonatal pigs and indicate that under the conditions of this study the apparent MCR of ipPRL and ipGH are similar but change significantly during early development.

Thirty-six crossbred gilts (71.7 [+ or -] .9 kg and 140.1 [+ or -] .9 d) were assigned to one of three doses (0, 35, or 70 [micro]g.kg [BW.sup.-1.d.sup.-1]) of recombinant porcine somatotropin (rpST). The doses of rpST were adjusted weekly, and i.m. injections continued until d 50. Gilts were pen fed (six gilts/pen) a 17% CP cornsoybean diet (1.2% lysine and 3.2 Mcal of ME/kg). At d 50, feed intake, feed:gain ratios (P =.02), and blood urea nitrogen were decreased (P < . 001) by increasing rpST doses, whereas ADG was increased (P = .04) by increasing rpST doses. Injections of rpST did not affect (P > .05) conception rate, age, or weight at puberty. Numbers of blastocysts or corpora lutea observed at d 10.4 [+ or -] 1.5 of gestation (42.2 d after final rpST injection) were unaffected (P > .05) by rpST treatment. Anterior and posterior pituitary weights were increased (P [< less than or equal to] .003) linearly with rpST dose. However, liver, adrenal, and heart weights were unaffected (P >.05) by rpST. After a withdrawal period of 42.2 [+ or -] 2.0 d, rpST increased (P [less than or equal to] .02) the estimated percentage of lean by 5.8% and longissimus muscle area by 10.4%. Eighteen hours before the initial rpST injection (d 0), 10 gilts per rpST dose were catheterized. Catheterizations were repeated on d 40. The rpST or diluent was given i.m. in the extensor muscle of the neck 1 h after initiation of blood collection. Adrenocorticotropic hormone (1.4 IU/kg BW) was administered through the catheter 3 h after initiation of blood collection. Mean serum concentrations of growth hormone and IGF-I increased linearly (P < .01) with rpST dose on d 0 and 40 of treatment. Mean area under the cortisol curve after both rpST and ACTH was similar (P =.84) among treatment groups on both d 0 and 40. Mean serum concentrations of LH and FSH were similar among treatment groups on both d 0 and 40, but they were higher on d 0 than on d 40 (P = .03 and P = .003 for LH and FSH, respectively). Percentages of acidophils, basophils, and chromophobes in the anterior pituitary gland were similar (P > .15) among treatments 42 d after rpST withdrawal. However, the percentage of somatotrophs increased (P < .001) and the percentage of lactotrophs decreased (P < .001) linearly with increasing rpST. Width of the glomerulosa and fasciculata zones of the adrenal cortex tended ( P < .10) to differ among treatments. Overall, positive nutritional advantages for replacement gilts in both growth and carcass traits were found in gilts that received rpST without any detrimental effects on reproduction. In addition, chronic rpST increased pituitary somatotrophs after withdrawal and tended to increase the width of glomerulosa and fasciculata zones in the adrenal cortex without affecting basal or induced release of cortisol.

The femur, a rib, and a third metacarpal were collected from 108 barrows (initial weight = 57 kg) and analyzed to determine the effects of porcine somatotropin (pST) and dietary lysine on bone mineralization and mechanical properties. In Exp. 1, pigs were injected daily with 4 mg of pST and fed diets containing 1.0% Ca and .9% P and either .6, .8, 1.0, 1.2, or 1.4% lysine. Control pigs (placebo injection) received the .6% lysine diet. Bone wall thickness (BWT) of the femur increased (linear, P |is less than~ .05) but ash content decreased (linear, P |is less than~ .10) as dietary lysine level increased. Stress and ash content of the rib also decreased (linear, P |is less than~ .05) with increasing dietary lysine level. In Exp. 2, pigs were injected with either 4 or 8 mg/d of pST and fed diets containing 1.1% Ca and 1.0% P and either .8, 1.0, 1.2 or 1.4% lysine. Control pigs received the .8% lysine diet. Increasing pST dosage increased BWT of the femur (linear, P |is less than~ .10) but decreased ash content (linear, P |is less than~ .10). In the rib, increasing pST dosage reduced stress, modulus of elasticity (linear, P |is less than~ .10), and ash content (linear, P |is less than~ .01). Increasing lysine level resulted in increased BWT of the femur and decreased ash content of rib, femur, and metacarpal (linear, P |is less than~ .10). These data indicate that pST administration in conjunction with increasing lysine levels decreases bone ash content but increases BWT of finishing pigs. Introduction Porcine somatotropin (pST) exerts its effects on growth performance and carcass traits by altering carbohydrate, protein, lipid, and mineral metabolism. These changes result in improvements in growth rate, efficiency, and carcass quality of pigs treated with pST (Etherton et al., 1987; Evock et al., 1988; Goodband et al., 1990, 1993). Although the changes in protein and adipose tissue growth are well documented, little is known about the effects of pST on bone development. Bryan et al. (1989) reported mobility problems in gilts after long-term (up to 65 d) daily administration of 70 |mu~g of pST/kg BW. Similar mobility problems were observed in approximately 50% of pigs treated with |is greater than~ 70 |mu~g of pST/kg BW for 77 d (Evock et al., 1988). Recently, Caperna et al. (1989) reported increased bone weight of femurs from pST-treated pigs; however, the increased weight apparently was a result of increased water content of the bone. Because pST increases the lysine requirement of finishing pigs (Goodband et al., 1990, 1993), Ca and P allowances also may be affected. Schricker (1990) observed no response in growth performance of finishing pigs injected with pST and fed increasing dietary P; however, bone mineralization was enhanced by increased P level, and pST administration increased bone wall thickness. Mechanical properties such as stress (strength) and elasticity were not evaluated. Therefore, this study was conducted to examine the effects of pST administration and dietary lysine level on bone mineralization and mechanical properties in finishing pigs. Experimental Procedures Animals. A total of 108 barrows (initial weight = 57 kg) were used in two experiments. Pigs were allotted by weight and ancestry in a randomized complete block design to experimental treatments and were housed in 4.6-m x 1.2-m pens in an open-front building with solid concrete floors. Drip coolers were controlled thermostatically, and pigs were allowed ad libitum access to feed and water. Table 1. Chemical analyses of control diets, % (Exp. 1 and 2)(a) Component Exp. 1 Exp. 2 DM 89.82 89.07 CP 17.78 17.8 0 Ether extract 13.52 9.93 Crude fiber 6.60 5.60 Ash 4.30 5.60 Ca 1.00 1.10 P .90 1.00 Essential and semiessen tial amino acids Arginine 1.82 1.32 Cyst ine .33 .31 Histidine .61 .45 Isoleucine . 72 .90 Leucine 1.52 1.64 Lysine .60 .80 Methionine .35 .45 Phenylalanine .87 .95 Tyrosine .33 .74 Threonine .80 .90 Tryptophan .22 .22 Valine .89 .90 a Values are expressed on an as-fed basis. Experiment 1. Experimental treatments consisted of daily injections of 4 mg of recombinant pST in combination with a corn-sesame meal diet (.6% lysine, 17.7% CP; Table 1) or diets containing .8, 1.0, 1.2, or 1.4% lysine provided by additions of L-lysine HCl. There were two pigs per pen and three pens per treatment. Calcium and P levels were analyzed to be 1.0 and .9%, respectively. The .6% lysine diet was formulated to contain twice the recommended level of amino acids (other than lysine), vitamins, and minerals for finishing pigs (50 to 110 kg; NRC, 1988). Serum samples were obtained 3 h after injection from pigs via vena cava puncture on d 14, 28, and on the last day of pST administration (pen mean weight 105 kg). Alkaline phosphatase activity (APA) was determined according to procedures described by Morgenstern et al. (1965). Pigs were injected daily in the extensor muscle of the neck until the pen mean weight reached 105 |+ or -~ 2 kg, at which time injections were terminated and a 7-d withdrawal period was initiated. Pigs were slaughtered in three groups at 7-d intervals. The femur, third rib, and third metacarpal were removed from the right side of each carcass, labeled, and frozen for later analyses. Experiment 2. Seventy-two barrows were allotted to experimental treatments arranged in a 2 x 4 factorial with a control treatment. Main effects included pST dosage (4 or 8 mg/d) and dietary lysine level (.8, 1.0, 1.2, and 1.4%). There were two pigs per pen and four pens per treatment. Control pigs (placebo injection) received the .8% lysine diet. Diets were formulated to contain |is greater than or equal to~ 200% of the NRC (1988) requirements for finishing pigs for all nutrients except lysine. Levels of Ca and P were 1.1 and 1.0%, respectively. All other procedures were as described for Exp. 1, with the exception that the first rib was collected instead of the third. Bone Analyses. Bones were allowed to thaw at 4|degrees~C overnight and manually cleaned of connective tissues. Bones were stored in plastic bags while being thawed but were allowed to dry at room temperature for approximately 30 min before determination of mechanical properties using an Instron Universal Testing Machine (Instron, Canton, MA). Crosshead speed was 5 mm/min. All calculations for bending moment, stress, strain, modulus of elasticity, and bone wall thickness were determined using formulas and methods described by Crenshaw et al. (1981a, b). Bones were cleaned of any remaining connective tissue, extracted in petroleum ether for 48 h, and dried in an oven at 38|degrees~C. From the femur, a 10-cm section was taken midshaft, and the marrow was removed before lipid extraction. All bones were ashed at 12 600|degrees~C for h. Ash is expressed as a percentage of the dried, fat-free bone. Statistical Analysis. Data were analyzed using the (GLM procedure of SAS (1985). Linear, quadratic, and cubic comparisons of treatment means were made for pST-treated pigs, whereas control pigs were compared to pST-treated pigs fed .6% lysine by using a nonorthogonal contrast. In Exp. 2, data analyses were conducted according to the methods described by Milliken and Johnson (1984) as a 2 x 4 factorial with a control treatment. Linear, quadratic, and cubic comparisons of treatment means were made for lysine main effects, and linear and quadratic comparisons were conducted for pST treatment means. Results Growth performance and carcass characteristics of the pigs have been described previously (Goodband et al., 1990, 1993). In Exp. 1, control pigs had higher APA (P |is less than~ .10) than pST-treated pigs fed .6% lysine by d 28 and at the conclusion of the experiment (Table 2). Bending moment of the femur decreased then increased (quadratic, P |is less than~ .10) as lysine level increased (Table 3). A similar trend (P |is greater than~ .20) was observed for stress and modulus of elasticity. Ash content of the femur decreased (linear, P |is less than~ .10), but bone wall thickness increased (linear, P |is less than~ .05) as dietary lysine increased. Bending moment of the rib was unaffected by experimental treatment (P |is greater than~ .30); however, stress and ash content decreased (linear, P |is less than~ .05) with increasing lysine level. Strain of the rib tended to increase, then decrease (quadratic, P |is less than~ .10) with increasing lysine level. Mechanical properties and ash content of the metacarpal were unaffected by experimental treatment with the exception of strain, which decreased (linear, P |is less than~ .05) as lysine level increased. TABULAR DATA OMITTED In Exp. 2, APA was not affected by pST dosage; however, it was decreased (linear, P |is less than~ .05) on d 14 and at the end of the experiment as dietary lysine level increased. No pST x lysine interactions were observed with the exception of bending moment of the metacarpal (P |is less than~ .05). Bending moment of the femur tended to increase (P |is greater than~ .20) with increasing pST dosage and dietary lysine level. Modulus of elasticity tended (P |is greater than~ .20) to decrease with increasing lysine level. Ash content of the femur was decreased (linear, P |is less than~ .10) with increasing lysine level. Bone wall thickness increased as lysine level increased (linear, P |is less than~ .01) and as pST dosage increased (linear, P |is less than~ .10). Bending moment of the rib was unaffected by experimental treatment; however, stress and modulus of elasticity decreased as pST dosage increased (linear, P |is less than~ .10). Ash content of the rib also was reduced by pST (linear, P |is less than~ .01) and increasing lysine level (linear, P |is less than~ .10). Metacarpal bending moment of pigs injected with 8 mg/d of pST was similar across lysine levels (range of 111 to 126 kg). However, metacarpal bending moment of pigs injected with 4 mg/d of pST was more variable (105 to 143 kg), which may have accounted for the interaction (P |is less than~ .05). Stress and modulus of elasticity tended to decrease (P |is greater than~ .25) with increasing pST dosage but increased and then decreased (quadratic, TABULAR DATA OMITTED TABULAR DATA OMITTED P |is less than~ .10) as lysine level increased. Ash content of the metacarpal also was decreased by increasing lysine level. Bone wall thickness of the metacarpal decreased and then increased (quadratic, P |is less than~ .10) with increasing pST dosage. Discussion Our data indicate an alteration in bone strength and mineralization in response to pST and dietary lysine. These effects are a direct response to pST administration and changes in growth rate because Ca and P levels were identical between treatments within experiments. In both experiments, APA tended to decrease with increasing lysine level. However, only in Exp. 1 did APA concentration fall significantly below values for control pigs. This response was unexpected, based on the increased bone wall thickness observed. Porcine somatotropin administration has been shown to increase the concentration of insulin-like growth factor I (IGF-I; Chung and Etherton, 1986; Walton et al., 1987; Evock et al, 1988), which is a potent stimulator of osteoblast proliferation (McCarthy et al., 1989). Alkaline phosphatase is secreted by osteoblasts during active bone formation, such as during rapid growth and after a major bone fracture (Guyton, 1961). Therefore, increased bone wall thickness is TABULAR DATA OMITTED probably in part a result of IGF-I-stimulated osteoblast proliferation, and APA would be expected to increase relative to that of control pigs. Alkaline phosphatase activity of boars fed various Ca:P ratios (Nimmo et al., 1980) suggested that lowered mineralization was correlated with high APA. We have no explanation for the decreased APA and the concurrent increase in bone wall thickness in pST-treated pigs fed higher lysine levels. Higher IGF-I concentrations, stimulated by exogenous pST and adequate nutrient density (Buonomo and Baile, 1987), would stimulate collagen formation (McCarthy et al., 1989), as observed by the greater bone wall thickness of the faster-growing pigs. Because the bones had thicker walls, bending moment was unaffected. However, when changes in bone diameter were accounted for in calculations for stress, actual bone strength decreased. This corresponds with the decreased modulus of elasticity observed, indicating that the faster-growing pigs had more pliable bones. Growing boars have been shown to have bones with greater wall thickness but less strength and mineralization than bones of barrows or gilts (Liptrap et al., 1970; Crenshaw et al., 1981b). This suggests that mineralization may not be able to keep up with bone matrix growth in faster-growing pigs, which would explain our results. Decreased mineralization may also be caused by differences in physiological maturity based on growth rate of pST-treated pigs. Because pST administration effectively inhibits initiation of the 'fattening' phase in the pig's growth curve, perhaps bone development proceeds at an enhanced rate similar to the increased protein accretion. Thus, bones of pST-treated pigs may still have been growing rapidly compared with those of control pigs. A second hypothesis regarding decreased mineralization of bones from pST-treated pigs involves prioritization of nutrients to more essential body functions. Pigs treated with porcine somatotropin have elevated concentrations of blood metabolites and hormones, which may increase cellular Ca and P requirements, thus making less Ca and P available for bone growth. In support of this, increased P in longissimus muscle samples from pST-treated pigs has been observed (Goodband et al., 1990). Bones of the axial skeleton are more responsive to demineralization than are long bones of the extremities (Mahan and Fetter, 1982; Maxson and Mahan, 1986). Ribs from pigs in both the present experiments had decreased stress; however, all bones examined showed similar trends in bending moment and modulus of elasticity. Ash content also was decreased in all bones, with the exception of the metacarpal in Exp. 2. In previous studies in which leg weakness and mobility problems have been observed (Evock et al., 1988; Bryan et al., 1989), higher dosages of pST were used for longer periods of time and lower dietary Ca and P levels (.70 and .65% calculated, respectively) were provided than in our studies. These conditions may increase the potential for mobility problems in pigs, as indicated by the changes in mechanical properties and bone mineralization in our study. Increased dietary P concentrations (.4 to .8%) have been shown to have no effect on growth performance of pST-treated pigs; however, bone ash and bone wall thickness were enhanced at the .6 and .8% P level (Schricker, 1990). Furthermore, no improvements have been reported in growth performance of pST-treated pigs compared to control pigs in response to increasing dietary Ca and P levels (Carter et al., 1991). However, pST-treated pigs required higher dietary Ca and P levels to maximize bone strength and mineralization (Carter et al., 1991). To achieve maximum longevity of sows, research has suggested that concentrations of Ca and P for growing gilts greater than those required to enhance growth performance are needed (Reinhard et al., 1976). This would maximize bone ash and strength and provide a Ca and P reservoir to buffer the negative Ca and P balance that occurs during lactation. Extrapolation of our results suggests that the longevity of pST-treated gilts kept in the breeding herd may be shorter than that of untreated gilts, because bone ash and strength were not maximized in barrows. However, because pST stimulated the growth of the collagen matrix, there may be potential for compensatory mineralization after gilts are selected for breeding. This compensatory response has been observed in pigs fed inadequate Ca and P levels during the growing phase, followed by adequate Ca and P levels during the finishing phase (Cera and Mahan, 1988). Recent research (Weeden et al., unpublished data) confirms that pST-treated gilts had thicker, more elastic bones than control gilts. However, during a 35-d period after pST administration, bone strength (stress) increased in pST-treated gilts, indicating compensatory mineralization. Further research is necessary to determine the Ca and P levels necessary during the finishing and postfinishing (prebreeding) periods to maximize bone mineralization, if pST is to be administered to replacement gilts. Implications Porcine somatotropin and dietary lysine alter the rate, efficiency, and composition of gain in swine. Furthermore, bone growth is affected, resulting in weaker, more elastic, and less mineralized bones in barrows treated with porcine somatotropin. However, bone wall thickness is increased by somatotropin administration and increased dietary lysine level. Literature Cited Bryan, K. A., J. M. Hammond, S. Canning, J. Mondschein, D. E. Carbaugh, A. M. Clark, and D. R. Hagen. 1989. Reproductive and growth responses of gilts to exogenous porcine pituitary growth hormone. J. Anim. Sci. 67:196. Buonomo, F. C., and C. A. Baile. 1987. Influence of nutrient deprivation on insulin-like growth factors I and II (IGF-I and IGF-II), somatotropin (GH) and metabolic hormones in swine. J. Anim. Sci. 65(Suppl. 1):300 (Abstr.). Caperna, T. J., R. G. Campbell, and N. C. Steele. 1989. Interrelationships of exogenous porcine growth hormone administration and feed intake level affecting various tissue levels of iron, copper, zinc and bone calcium of growing pigs. J. Anim. Sci 67: 654. Carter, S. D., G. L. Cromwell, and T. S. Stahly. 1991. Effects of pST administration on the calcium and phosphorus requirements of finishing pigs. J. Anim. Sci. 69(Suppl. 1):384 (Abstr.). Cera, K. R., and D. C. Mahan. 1988. Effect of dietary calcium and phosphorus level sequences on performance, structural soundness and bone characteristics of growing-finishing swine. J. Anim. Sci. 66:1598. Chung, C. S., and T. D. Etherton. 1986. Characterization of porcine growth hormone (pGH) binding to porcine liver microsomes: Chronic administration of pGH induces pGH binding. Endocrinology 119:780. Crenshaw, T. D., E. R. Peo, Jr., A. J. Lewis, and B. D. Moser. 1981a. Bone strength as a trait for assessing mineralization in swine: A critical review of techniques involved. J. Anim., Sci. 53:827. Crenshaw, T., D., E. R. Peo, Jr., A. J. Lewis, B. D. Moser, and D. Olson. 1981b. Influence of age, sex and calcium and phosphorus levels on the mechanical properties of various bones in swine. J. Anim. Sci. 52:1319. Etherton, T. D., J. P. Wiggins, C. M. Evock, C. S. Chung, J. F. Rebhun, P. E. Walton, and N. C. Steele. 1987. Stimulation of pig growth performance by porcine growth hormone: Determination of the dose-response relationship. J. Anim., Sci. 64:433. Evock, C. M., T. D. Etherton, C. S. Chung, and R. E. Ivy. 1988. Pituitary porcine growth hormone (pGH) and a recombinant pGH analog stimulate pig growth performance in a similar manner. J. Anim. Sci. 66:1928. Goodband, R. D., J. L. Nelssen, R. H. Hines, D. H. Kropf, G. R. Stoner, R. C. Thaler, A. J. Lewis, and B. R. Schricker. 1993. Interrelationships between porcine somatotropin and dietary lysine on growth performance and carcass characteristics of finishing swine. J. Anim. Sci. 71:663. Goodband, R. D., J. L. Nelssen, R. H. Hines., D. H. Kropfl, R. C. Thaler. B. R. Schricker, G. E. Fitzner, and A. J. Lewis. 1990. The effects of porcine somatotropin and dietary lysine on growth performance and carcass characteristics of finishing swine. J. Anim. Sci. 68:3261. Guyton, A. C. 1961. Textbook of Medical Physiology (4th Ed.). W. B. Saunders, Philadelphia, PA. Liptrap, D. O., E. R. Miller, D. E. Ullrey, K. K. Keahey, and J. A. Hoefer. 1970. Calcium level for developing boars and gilts. J. Anim. Sci. 31:540. Mahan, D. C., and A. W. Fetter. 1982. Dietary: calcium and phosphorus levels for reproducing sows. J. Anim. Sci. 54:285. Maxson, P. F., and D. C. Mahan. 1986. Dietary calcium and phosphorous for lactating swine at high and average production levels. J. Anim. Sci. 63:1163. McCarthy, T. L., M. Centrel~a, and E. Canalis. 1989. Regulatory effects of insulin-like growth factors I and II on bone collagen synthesis and rat calvarial cultures. Endocrinology 24:301. Milliken, G. A., and D. E. Johnson. 1984. Analysis of Messy Data. Vol. I. Designed Experiments. Lifetime Learning Publ., Belmont, CA. Morgenstern, S., G. Kessler, J. Auerbach, R. V. Flor, and B. Klein. 1965. An automated p-nitrophenyl phosphate serum alkaline phosphatase procedure for the auto-analyzer. Clin. Chem. 11: 876. Nimmo, R. D., E. R. Peo, Jr., B. D., Moser, P. J. Cunningham, D. G. Olson, and T. D. Crenshaw. 1980. Effect of various levels of dietary calcium and phosphorus on performance, blood and bone parameters in growing boars. J. Anim. Sci. 51:100. NRC. 1988. Nutrient Requirement of Swine (9th Ed.). National Academy Press, Washington, DC. Reinhard, M. K., D. C. Mahan, B. L. Workman, J. H. Cline, A. W. Fetter, and A. P. Grifo, Jr. 1976. Effect of increasing dietary protein level, calcium and phosphorus on feedlot performance, bone mineralization and serum mineral values with growing swine. J. Anim. Sci. 43:770. SAS. 1985. SAS User's Guide: Statistics. SAS Inst. Inc., Cary, NC. Schricker, B. R. 1990. PST: Production potential. Large Anim. Vet. 45(3):13. Walton, P. E., T. D. Etherton, and C. S. Chung. 1987. Exogenous pituitary and recombinant growth hormones induce insulin and insulin-like growth factor I resistance in pig adipose tissue. Domest. Anim. Endocrinol. 4(3):183.

Seventy-two barrows (initial weight = 57.1 kg) were used to determine the interrelationship between porcine somatotropin (pST) and dietary lysine and their effects on growth performance and carcass characteristics. Pigs were injected daily in the extensor muscle of the neck with either 4 or 8 mg of pST and fed a pelleted corn-soybean meal-sesame meal diet (.8% Lysine; 17.8% CP) or diets containing 1.0, 1.2, or 1.4% lysine provided by additions of L-lysine HCl (2 x 4 factorial arrangement). Control pigs (placebo injection) received the .8% lysine diet. All diets were formulated to contain |is greater than or equal to~ 200% of current recommendations for other amino acids, vitamins, and minerals. A tendency for a pST x lysine interaction was observed for cumulative ADG (P |is less than~ .15) and feed conversion (G/F; P |is less than~ .05). Average daily gain and G/F were improved by increasing dietary lysine level in pigs injected with 4 mg/d of pST; however, pigs injected with 8 mg/d of pST had greater improvements in cumulative ADG and G/F with added lysine. Feed intake was reduced (quadratic, P |is less than~ .10) as dietary lysine level and pST dosage increased. Increasing pST dosage and dietary lysine increased (linear, P |is less than~ .05) longissimus muscle area and decreased backfat thickness. Trimmed ham and loin weights were increased (linear, P |is less than~. 10) by pST dosage. Chemical composition of samples taken from the loin, ham, and belly indicated increased moisture and CP and decreased lipid content as pST dosage and dietary lysine level increased (quadratic, P |is less than~ .05). Shear force values from loin and semimembranosus increased with increasing lysine level (quadratic, P |is less than~ .01) and pST dosage (linear, P |is less than~ .05); however, these differences were not detected by sensory analysis (P |is greater than~ .20). Plasma urea concentrations on d 28 decreased with increasing lysine level (quadratic, P |is less than~ .05), and plasma lysine concentrations increased (linear, P |is less than~ .01). Based on the pST x lysine interaction for ADG and G/F, these data suggest that the lysine level needed to maximize growth performance and carcass characteristics may be proportional to the pST dosage provided. Growth and carcass characteristics were maximized by dietary lysine intakes of 27 to 32 and |is greater than or equal to~ 36 g/d for pigs injected with 4 and 8 of mg/d of pST, respectively. Introduction The feasibility of using porcine somatotropin (pST) as a growth promotant in swine has raised many questions about the effect it will have on the swine industry. One area that is beginning to be defined is the effect of diet and nutrient density on lean tissue deposition and adipose tissue growth in finishing pigs injected with pST. Recent results indicate that the lysine requirement of finishing pigs injected with 4 mg/d of pST is approximately 25 to 30 g/d (Goodband et al., 1990). However, the lysine requirement of finishing pigs may be proportional to their potential for lean tissue deposition, which can be affected by the quantity of pST administered. Consequently, the amount of pST administered may influence the lysine requirement. It would seem that some previous experiments that have evaluated the effects of pST on pig performance may have been confounded by inadequate intakes of amino acids (Kraft et al., 1986; Wolfrom et al., 1986; Smith et al., 1987). Thus, the asymptotic response in growth performance of finishing pigs to increasing quantities of exogenous pST may be a result of inadequate dietary amino acid levels. Therefore, the objectives of this study were to evaluate the performance of finishing pigs treated with different dosages of pST in combination with various levels of dietary lysine and to determine whether responses to increasing pST dosage were affected by dietary lysine level. Experimental Procedures Animals. Seventy-two barrows, averaging 57 kg, were allotted on the basis of initial weight an ancestry in a randomized complete block design to one of nine experimental treatments. Treatments were arranged in a 2 x 4 factorial with a control treatment. Main effects were pST dosage and dietary lysine level. There were two pigs per pen providing four observations per treatment (pen was considered the experimental unit). Pigs were housed in 4.6-m x 1.2-m pens in a modified open-front building with solid concrete floors and allowed ad libitum access to feed and water. Experimental treatments consisted of daily injections of either 4 or 8 mg of recombinant pST in combination with a corn-soybean meal-sesame meal diet (.8% lysine, 17.8% CP; Table 1) or diets containing 1.0, 1.2, or 1.4% lysine provided by additions of L-lysine HCl. The chemical composition of the .8% lysine diet (control) was determined by AOAC (1984) procedures (Table 2). Amino acid analysis was determined by ion-exchange chromatography after acid hydrolysis. Cystine and methionine were determined after oxidation with performic acid (Moore, 1963). The control diet was calculated to meet the estimated requirement for lysine but to contain twice the requirements (NRC, 1988) of all other amino acids. Amino acid analysis indicated that all amino acids (other than lysine) exceeded the pig's estimated requirement by 200%. Table 1. Composition of control diet(a) Ingredient Perce ntage Corn 60.98 Soybean meal (44% CP) 18.30 Sesame meal 10.00 Soybean oil 5.00 Monocalcium phosphate 2.77 Limestone .78 Salt .50 Trace mineral premix(b) .20 Vitamin premix(c) .5 0 Selenium premix(d) .05 Threonine .10 Methionine .05 Sucrose .77 Total 100.00 a Dietary lysine l evels 1.0, 1.2, and 1.4% were formulated by adding .26, .52, and .77 L-lysine HC l at the expense of sucrose. b Provided the following per kilogram of complete d iet: Ca, 220 mg; Fe, 440 mg; Zn, 440 mg; Mn, 440 rag; Cu, 44 rag; I, 13.2 mg; an d Co, 4.4 mg. c Provided the following per kilogram of complete diet: vitamin A, 11,023 IU; vitamin D, 1,102 IU; vitamin E, 44 IU; menadione, 4.4 mg; riboflavin , 11 mg; D-panthothenic acid, 27.6 mg; niacin 60.6 mg; choline, 1,102 mg; and vi tamin |B.sub.12~, .55 mg. d Provided .3 mg of Se per kilogram of complete diet. Table 2. Chemical analyses of control diet(a) Component Percentage DM 89.07 CP 17.80 Ether extract 9.93 Crude fiber 5.60 Ash 5.60 Ca 1.10 P 1.00 Essential and se miessential amino acids Arginine 1.32 Cyst ine .31 Histidine .45 Isoleucine .90 Leucine 1.64 Lysine .80 Methionine .45 Phenylalanin e .95 Tyrosine .74 Threonine .90 Tryptophan .22 Valine .90 a Values are expressed on an as-fed basis. Porcine somatotropin was dissolved in buffer 14 d before initiation of the study and stored frozen to ensure stability. Before use, the daily allotment of pST was allowed to thaw overnight at 4|degrees~C. Pigs were injected daily between 0600 and 0700 in the extensor muscle of the neck. The contralateral muscle was injected on alternate days. Pigs and feeders were weighed on d 14 and 28 and then weekly until the mean weight of the two pigs in a pen reached 105 |+ or -~ 2 kg. Daily injections were terminated at this time, and a 7-d withdrawal period was initiated. Blood Sampling. Serum and plasma samples were obtained on d 14 and 28 and on the last day of pST administration. Analyses for glucose, urea, free fatty acids (FFA), creatinine, insulin, somatotropin, and triiodothyronine (|T.sub.3~) were conducted as described previously (Goodband et al., 1990). Interassay CV were .6, 1.3, and 6.6% for somatotropin, insulin, and |T.sub.3~, respectively. Carcass Data Collection. On the last day of pST administration, all pigs were ultrasonically scanned (Technicare 210 DX, Johnson & Johnson, Englewood, CO) for backfat thickness adjacent to the first and last ribs and last lumbar vertebra. The three measurements were then averaged and adjusted to a constant weight (104 kg) using NPPC (1988) procedures. In addition, backfat depth was also measured at the 10th rib approximately 6 cm from the midline. Backfat was measured at this time because pigs were skinned at slaughter. Pigs were slaughtered in six groups of 12 pigs each over a 26-d period. Carcass measurements, muscle dissection, sampling procedures, shear force determination, and sensory panel evaluations were conducted as previously described (Goodband et al., 1990). In the sensory analysis, an incomplete block design (Snedecor and Cochran, 1980) was used to assign daily sampling order to treatments to allow panelists to evaluate six chops per day. Statistical Analysis. Data were analyzed using the GLM procedure of SAS (1985). Analysis was conducted according to procedures described by Milliken and Johnson (1984) as a 2 x 4 factorial with a control treatment. Linear, quadratic, and cubic comparisons of treatment means for lysine level were evaluated among pST-treated pigs, whereas linear and quadratic caparisons were made among control pigs and pigs treated with 4 or 8 mg of pST. Sensory analysis and carcass measurement adjustments were described previously (Goodband et al., 1990). Results Growth Performance. A pST x lysine interaction was observed for d-28 ADG (P |is less than~ .05); similar numeric trends were observed (P |is less than~ .15) on d 14 and overall (Table 3). This seemed to be the result of the relatively small increase in ADG for pigs injected with 4 mg/d of pST compared with the larger increase to added lysine observed in pigs injected with 8 mg/d. Overall ADFI was decreased by increasing pST dosage (quadratic, P |is less than~ .10) and increasing lysine level (quadratic, P |is less than~ .05). A pST x lysine interaction was observed for d-28 and overall G/F (P |is less than~ .05); injection of 8 mg/d of pST resulted in a greater improvement in G/F than injection of 4 mg/d. The administration of pST (both 4 and 8 mg/d) improved G/F (quadratic, P |is less than~ .05) throughout the study compared with the placebo injections. Blood Metabolites. No pST x lysine interactions (P |is greater than~ .20) were observed for plasma urea, glucose, FFA, or creatinine concentrations (Table 4). Plasma urea concentrations decreased as pST dosage increased (quadratic, P |is less than~ .05). Plasma urea concentrations (d 28 and final bleeding) also were decreased by increasing dietary lysine level (quadratic, P |is less than~ .05). In pigs injected with 4 mg/d of pST, urea concentration on d 28 decreased and then increased as dietary lysine increased. However, in pigs injected with 8 mg/d of pST, urea concentrations reached a plateau at 1.0% dietary lysine and remained unchanged at either 1.2 or 1.4% lysine. Glucose concentrations were elevated in pST-treated pigs at all sampling times (quadratic, P |is less than~ .05) but were unaffected by dietary lysine level. TABULAR DATA OMITTED Plasma FFA concentrations increased (linear, P |is less than~ .05) as dietary lysine level increased and tended to be increased by pST dosage (d 28, linear, P |is less than~ .05). Creatinine concentrations were reduced (quadratic, P |is less than~ .05) in the serum of pST-treated pigs compared with that of control pigs. TABULAR DATA OMITTED Plasma lysine concentrations on d 28 increased (linear, P |is less than~ .05) as dietary lysine increased (Table 5). Histidine was the only other amino acid to be affected by dietary lysine level (linear, P |is less than~ .05). Leucine, threonine, and valine concentrations decreased as pST dosage increased (linear, P |is less than~ .05), whereas methionine concentration decreased then increased (quadratic, P |is less than~ .10). Plasma somatotropin concentrations increased with increasing pST dosage (linear, P |is less than~ .05; Table 6). Increasing dietary lysine level tended (linear, P |is less than~ .10) to lower somatotropin concentrations in serum samples collected at termination of daily injections. Insulin concentrations were elevated by increasing TABULAR DATA OMITTED pST dosage (linear, P |is less than~ .05; quadratic, P |is less than~ .10) and also increased (linear, P |is less than~ .10) as dietary lysine level increased. Triiodothyronine concentrations increased numerically (P |is greater than~ .15) as lysine level increased. Increasing pST dosage increased (linear, P |is less than~ .05) |T.sub.3~ concentrations in serum. Carcass Data. Although pigs were slaughtered at a constant weight, hot carcass weight and chilled carcass weight were decreased (quadratic, P |is less than~ .05) by increasing pST dosage (Table 7). Dietary lysine level had no effect on carcass weight. Control pigs had the heaviest hot and chilled carcass weights. This resulted in decreased dressing percentage of pigs injected with either 4 or 8 mg/d of pST (linear, P |is less than~ .05; quadratic, P |is less than~ .10). Control pigs had greater average backfat and 10th rib fat depth than pigs injected with either 4 or 8 mg of pST (linear, P |is less than~ .05). Increasing dietary lysine reduced average and 10th rib backfat (linear, P |is less than~ .05). Longissimus muscle area increased with increasing pST dosage (linear, P |is less than~ .05) and tended to increase with dietary lysine level (linear, P |is less than~ .15). Carcass length was unaffected by experimental treatments. Kidney fat weight decreased at pST dosage increased (quadratic, P |is less than~ .05) and also tended to decrease with increasing dietary lysine level (linear, P |is less than~ .15). Trimmed weights of the ham and loin tended to TABULAR DATA OMITTED increase with increasing pST dosage (linear, P |is less than~ .10) and dietary lysine level (linear, P | is less than~ .15). Weights of the semitendinosus, adductor, and quadriceps femoris muscles and lean trim were increased (linear, P |is less than~ .05) by pST dosage (Table 8). Color scores from the ham increased as pST dosage increased (linear, P |is less than~ .05); however, a pST x lysine interaction was observed for longissimus color scores (P |is less than~ .05). This seemed to be a result of a greater change in color score in pigs treated with 4 mg/d of pST than observed in pigs treated with 8 mg/d of pST. Ham firmness increased with increasing pST dosage (linear, P |is less than~ .10) and dietary lysine (linear, P |is less than~ .01), whereas longissimus firmness increased then decreased as lysine level increased (quadratic, P |is less than~ .05). These changes in longissimus color and firmness correspond with the pST x lysine interaction (P |is less than~ .05) observed for longissimus 24-h pH. As with backfat thickness, marbling scores decreased with increasing pST dosage (quadratic, P |is less than~ .10) and dietary lysine level (linear, P |is less than~ .10). TABULAR DATA OMITTED Composition of longissimus, belly, and individual ham muscles (semimembranosus, SM; semitendinosus, ST; and biceps femoris, BF) were affected by pST dosage and dietary lysine level (Table 9). Moisture content increased as pST dosage (quadratic, P |is less than~ .05) and dietary lysine level increased (linear, P |is less than~ .10) in all muscles except the SM. The increase in moisture was associated with a trend toward increased CP content, which was increased by lysine level (linear, P |is less than~ .05) and pST dosage (linear and quadratic, P |is less than~ .05), but only in the longissimus and belly. Lipid content was decreased in the longissimus, ST, BF, and belly samples by increasing pST dosage (quadratic, P |is less than~ .05). Lipid content of all muscles also was substantially reduced by increasing dietary lysine level (linear, P |is greater than~ .05). Ash content increased with pST and dietary lysine, but only in SM and belly samples. In general, the greatest response to pST and dietary lysine level was observed in belly samples, in which there was an increase of approximately 30% in CP and a reduction of 50% in lipid content for pigs treated with 8 mg/d of pST and fed 1.4% lysine compared with control pigs. Weights of the heart, liver, kidney, and spleen were increased (linear, P |is less than~ .05) by pST dosage (Table 10). Thaw losses were decreased in longissimus and SM samples by increasing pST dosage (linear, P |is less than~ .05; quadratic, P |is less than~ .10; Table 11). Drip cooking losses were decreased in longissimus samples by increasing pST dosage (quadratic, P |is less than~ .10), whereas evaporative TABULAR DATA OMITTED cooking losses were decreased in SM samples by increased lysine level (quadratic, P |is less than~ .10). This resulted in a decrease in total cooking losses in SM samples (quadratic, P |is less than~ .10). However, when combined, total cooking and thaw losses were unaffected by experimental treatment, although there were tendencies toward decreased total losses among pST-treated pigs as dietary lysine level increased. Shear force values increased with increasing pST dosage in longissimus and SM samples (linear, P |is less than~ .05) and increased as lysine level increased (quadratic, P |is less than~ .10; Table 12). However, these changes in shear force were not detected by sensory analysis, because scores for juiciness, flavor, and tenderness were unaffected by either pST dosage or lysine level (P |is greater than~ .25). TABULAR DATA OMITTED TABULAR DATA OMITTED Discussion These data confirm previous results indicating an improvement in growth performance and carcass characteristics of pST-treated pigs in response to additional lysine (Goodband et al., 1990). As in our previous experiment, performance of pigs injected with 4 mg/d of pST was maximized at a daily lysine intake of approximately 27 g. However, these data also indicate an interactive effect between pST and dietary lysine on gain and feed efficiency (pST x lysine interaction, P |is less than~ .05). When pST dosage was increased to 8 mg/d, pig performance continued to improve up to a lysine level of 1.4% (approximately 36 g/d). Based on the linear (P |is less than~ .05) nature of the response to added lysine, it would seem that pigs injected with 8 mg/d of pST may require more dietary lysine than the 1.4% provided in this experiment. Inadequate amino acid levels may have limited performance in other experiments and could account for some of the variation in response of pigs in pST administration (Kraft et al., 1986; Wolfrom et al., 1986; Smith et al., 1987). TABULAR DATA OMITTED Administration of pST decreased ADFI in a dose-dependent fashion. This response was similar to results from previous experiments (Etherton et al., 1986, 1987; Campbell et al., 1988). Feed intake was decreased by increasing dietary lysine level. This response may have been an attempt by pigs fed the .8% lysine diets to compensate for the inadequate lysine level by eating more feed (Baker, 1986). The elevations in plasma glucose concentrations are consistent with other experiments (Etherton et al., 1987; Campbell et al., 1988; Goodband et al., 1990) and are a result of altered hepatic glucose output and clearance (Gopinath and Etherton, 1989). Elevations in FFA and |T.sub.3~ concentrations paralleled changes observed in our previous experiment and support the current hypothesis that FFA uptake by adipose tissue is attenuated by the antagonism between pST and insulin in adipose tissue (Walton and Etherton, 1986). Thus, fat may be utilized to a greater extent in pST-treated pigs as an energy substrate. This would necessitate greater demand for oxygen, which would be supplied by |T.sub.3~-stimulated dissociation of oxygen from hemoglobin. Changes in plasma urea concentrations are typical of those observed in experiments to determine amino acid requirements of pigs (Lewis et al., 1980; Goodband et al., 1990). As dietary lysine increased and approached the pig's requirement, protein synthesis became more efficient, and other amino acids were incorporated into protein rather than being deaminated with the formation of urea. Plasma lysine concentrations were decreased in pST-treated pigs fed .8% lysine compared with control pigs, suggesting insufficient dietary lysine intake. However, plasma lysine concentrations increased in pST-treated pigs as dietary lysine increased above 1.0%, suggesting that the pig's lysine requirement was met or exceeded. Surprisingly, high plasma lysine concentrations were observed in pigs injected with 8 mg/d of pST and fed the 1.4% lysine diet despite increasing ADG and G/F. Plasma lysine values would be expected to increase sharply only after growth performance criteria had leveled off (Lewis et al., 1980; Asche et al., 1985; Baker, 1986). Furthermore, the range of plasma lysine concentrations, although similar to those observed in a previous study (Goodband et al., 1990), are much lower than values observed in the young pig (Lewis et al., 1980; Asche et al., 1985). The change in plasma lysine values in response to increasing dietary lysine observed in our study supports the hypothesis that pST administration, in addition to increasing the pig's amino acid requirement, may also alter the efficiency of amino acid utilization (Campbell et al., 1991). Other amino acid concentrations decreased in response to increasing pST dosage, which is similar to the response observed for plasma urea concentrations. Insulin concentrations were elevated as a result of increased glucose concentrations (Gopinath and Etherton, 1989), in agreement with previous experiments (Etherton et al., 1987; Evock et al., 1988; Goodband et al., 1990). Because all pigs were slaughtered at approximately the same weight, differences in carcass weight seemed to be caused by a reduction in skinned dressing percentage of pST-treated pigs. Dressing percentage values have been variable but in general are approximately 0 to 3% lower in pigs treated with pST than in control pigs (Evock et al., 1988; Bryan et al., 1989; Goodband et al., 1990). Dressing percentage would be expected to decrease, because pST-treated pigs were leaner and had increased organ weights. Responses in longissimus muscle area and backfat thickness were consistent with previous studies evaluating the effects of pST dosage on carcass traits (Etherton et al., 1987; Campbell et al., 1988; Evock et al., 1988) and also with studies showing that carcass leanness is increased by increasing dietary lysine (Williams et al., 1984; Asche et al., 1985; Goodband et al., 1990). However, as with ADG and G/F, backfat thickness and longissimus muscle area were improved to a greater extent when high-lysine diets were fed to pigs injected with 8 mg/d. Reductions in kidney fat paralleled those observed for backfat thickness, marbling score, and intramuscular lipid content. The changes observed in color, firmness, and 24-h pH in pST-treated pigs may indicate that a slightly higher 24-h pH resulted in slightly darker and firmer pork compared with that from control pigs. However, because color and firmness scores were still within an acceptable range of normal values, it is unlikely that treatments caused a predisposition toward DFD pork. Chemical composition of selected muscles was similar to that observed previously in pST-treated pigs fed added lysine (Goodband et al., 1990). The belly, one of the less economically important, fatter cuts of pork, seemed to show the greatest response to pST and dietary lysine. Little information is available on the effects of pST on such cuts of pork; however, our data indicate a potential to improve their quality. Cooking losses and sensory properties of pork from pST-treated pigs were unaffected by experimental treatment. These findings are consistent with previous data indicating little adverse effect on pST on pork quality (Beermann et al., 1988; Evock et al., 1988; Goodband et al., 1990). Our sensory panel evaluations seem to contradict those of DeVol et al. (1988), who found decreased tenderness and juiciness of pork containing |is less than~ 2.5% lipid. Longissimus samples from control and pST-treated pigs were on either side of this threshold value and yet no differences were distinguishable by the trained sensory panel. Implications These data further demonstrate that porcine somatotropin administration improves daily gain, feed conversion, and carcass characteristics of finishing pigs without adversely affecting pork quality. The response of finishing pigs to exogenous porcine somatotropin administration is dependent on the dietary lysine level provided. Pigs injected with 4 mg/d of porcine somatotropin require approximately 27 g/d of lysine, whereas pigs injected with 8 mg/d of porcine somatotropin require |is greater than or equal to~ 36 g/d of lysine to maximize growth performance and carcass leanness. Literature Cited AOAC. 1984. Official Methods of Analysis (14th Ed.). Association of Official Analytical Chemists, Arlington, VA. Asche, G. L., A. J. Lewis, E. R. Peo, Jr., and J. D. Crenshaw. 1985. The nutritional value of normal and high lysine corns for weanling and growing-finishing swine when fed at for lysine levels. J. Anim. Sci. 60:1412. Baker, D. H. 1986. Problems and pitfalls in animal experiments designed to establish dietary requirements for essential nutrients. J. Nutr. 116:2339. Beermann, D. H., G. Armbruster, R. D. Boyd, K. Roneker, and K. D. Fagin. 1988. Comparison of the effects of two recombinant forms of porcine somatotropin (pST) on pork composition and palatability. J. Anim. Sci. 66(Suppl. 1):281 (Abstr.). Bryan, K. A., J. M. Hammond, S. Canning, J. Mondschein, D. E. Carbaugh, A. M. Clark, and D. R. Hagen. 1989. Reproductive and growth responses of gilts to exogenous porcine pituitary growth hormone. J. Anim. Sci. 67:196. Campbell, R. G., R. J. Johnson, M. R. Taverner, and R. H. King. 1991. Interrelationships between exogenous porcine somatotropin (pST) administration and dietary protein and energy intake on protein deposition capacity and energy metabolism of pigs. J. Anim. Sci. 69:1522. Campbell, R. G., N. C. Steele, T. J. Caperna, J. P. McMurtry, M. B. Solomon, and A. D. Mitchell. 1988. Interrelationships between energy intake and endogenous porcine growth hormone administration on the performance, body composition and protein and energy metabolism of growing pigs weighing 25 to 55 kilograms live weight. J. Anim. Sci. 66:1643. DeVol, D. L., F. K. McKeith, P. J. Bechtel, J. Novakofski, R. D. Shanks, and T. R. Carr. 1988. Variation in composition and palatability traits and relationships between muscle characteristics and palatability in a random sample of pork carcasses. J. Anim. Sci. 66:385. Etherton, T. D., J. P. Wiggins, C. S. Chung, C. M. Evock, J. F. Rebhun, and P. E. Walton. 1986. Stimulation of pig growth performance by porcine growth hormone and growth hormone-releasing factor. J. Anim. Sci. 63:1389. Etherton, T. D., J. P. Wiggins, C. M. Evock, C. S. Chung, J. F. Rebhun, P. E. Walton, and N. C. Steele. 1987. Stimulation of pig growth performance by porcine growth hormone: Determination of the dose-response relationship. J. Anim. Sci. 64:433. Evock, C. M., T. D. Etherton, C. S. Chung, and R. E. Ivy. 1988. Pituitary porcine growth hormone (pGH) and a recombinant pGH analog stimulate pig growth performance in a similar manner. J. Anim. Sci. 66:1928. Goodband, R. D., J. L. Nelssen, R. H. Hines, D. H. Kropf, R. C. Thaler, B. R. Schricker, G. E. Fitzner, and A. J. Lewis. 1990. The effects of porcine somatotropin and dietary lysine on growth performance and carcass characteristics of finishing swine. J. Anim. Sci. 68:3261. Gopinath, R., and T. D. Etherton. 1989. Effects of porcine growth hormone on glucose metabolism of pigs: II. Glucose tolerance, peripheral tissue insulin sensitivity and glucose kinetics. J. Anim. Sci. 67:689. Kraft, L. A., D. R. Haines, and R. L. DeLay. 1986. The effects of daily injections of recombinant porcine growth hormone (rpGH) on growth, feed efficiency, carcass composition and selected metabolic and hormonal parameters in finishing swine. J. Anim. Sci. 63(Suppl. 1):218 (Abstr.). Lewis, A. J., E. R. Peo, Jr., B. D. Moser, and T. D. Crenshaw. 1980. Lysine requirement of pigs weighing 5 to 15 kg fed practical diets with and without added fat. J. Anim. Sci. 61:361. Milliken, G. A., and D. E. Johnson. 1984. Analysis of Messy Data. Vol. I. Designed Experiments. Lifetime Learning Publ., Belmont, CA. Moore, S. 1963. On the determination of cystine as a cysteic acid. J. Biol. Chem. 238 1:235. NPPC. 1988. Procedures to Evaluate Market Hog Performance (Revised 2nd Ed.). National Pork Producers Council, Des Moines, IA. NRC. 1988. Nutrient Requirements of Swine (9th Ed.). National Academy Press, Washington, DC. SAS. 1985. SAS User's Guide: Statistics. SAS Inst. Inc., Cary, NC. Smith, V. G., W. M. Moseley, C. W. Kasson, and D. D. Kratzer. 1987. Effect of exogenous recombinant bovine somatotropin (rbSt) and porcine pituitary somatotropin (ppSt) on growth performance of pigs. J. Anim. Sci. 65(Suppl. 1):243 (Abstr.). Snedecor,G. W., and W. G. Cochran, 1980. Statistical Methods (7th (Ed.). Iowa State University Press, Ames. Walton, P. E., and T. D. Etherton. 1986. Stimulation of lipogenesis by insulin in swine adipose tissue: Antagonism by porcine growth hormone. J. Anim. Sci. 62:1584. Williams, W. D. G. L. Cromwell, T. S. Stahly, and J. R. Overfield. 1984. The lysine requirement of the growing boar versus barrow. J. Anim. Sci. 58:657. Wolfrom, G. W., R. E. Ivy, and C. D. Baldwin. 1986. Effect of native porcine growth hormone (npGH) injected intramuscularly in barrows. J. Anim. Sci. 63(Suppl. 1):219 (Abstr.).

Ninety pigs were used to investigate the efficacy of long-term implants of porcine somatotropin (pST) in improving growth, feed:gain ratio, and carcass characteristics in pigs at three dose levels (0-, 100-, and 200-mg pST implant) from 71 to 99 kg live weight. The use of long-term implants did not alter (P |is greater than~ .05) growth rate. Administration of the 200-mg pST implant resulted in a 15% reduction in feed consumption, and this reduction was significant (P|is less than~ .05). The feed:gain ratio was improved (P |is less than~ .05) in pigs that received the 200- compared with O-mg pST implant (3.2 vs 2.62 of kg feed/kg of gain). In pigs that received the 200- or 100-mg pST implant, there was a reduction (P|is less than~ .05) in carcass weight; however, carcass length was similar (P |is greater than~ .05) regardless of pST treatment. Administration of the 200-mg pST implant resulted in 25 and 38% reductions (P|is less than~ .05) in last rib fat and leaf fat compared with the O-mg pST implant. The weights of kidneys and head were increased by the pST administration. The weights of wholesale cuts were not affected by the administration of the pST implant. However, separable skin and fat from the ham, loin, and picnic were lower (P |is less than~ .05) in pigs that received the 200-mg pST than in pigs that received the O-mg pST implant. Meat color and structure were similar across pST treatments, indicating that the use of long-term pST implants was not detrimental to meat quality. The results represent a significant step in the efficacious use of a long-term delivery system for pST as opposed to the laborious daily injection schedule. Introduction The discovery that exogenous administration of porcine somatotropin (pST) could preferentially alter body composition toward increased lean mass and decreased fat deposition (Machlin, 1972; Etherton et al., 1987; Boyd and Bauman, 1989; Evans et al, 1991) presented an opportunity for improving the efficiency of pork production. Recombinantly derived pST and pST extracted from the pituitary seem to have similar effects on growth performance and carcass characteristics when administered daily to pigs (Etherton et al. 1986). Numerous studies have shown that daily injections of pST enhance growth rate and feed efficiency, reduce feed consumption, and cause large changes in body composition (Machlin, 1972; Etherton et al., 1986, 1987; Campbell et al., 1989a,b; Evans et al., 1991). The alteration of body composition by enhancing leanness and reducing fat is important both for the diet-conscious consumer who wants wholesome, lean pork and the pork producer whose productive efficiency will be improved. In commercial swine operations, daily injections of pST would be laborious and would involve significant financial costs. The use of pST in a prolonged-delivery system presents an attractive option to daily injections. A long-term pST implant, compared to daily injections, would be less stressful to pigs and less costly in terms of labor requirement. In this paper, we report the growth performance and carcass responses of pigs to long-term implants of pST from 70 to 100 kg of live weight. Experimental Procedure Animals, Housing, and Porcine Somatotropin Implants. Forty-five barrows (average initial weight of 72 kg) and forty-five gilts (average initial weight of 71 kg) were allocated to 18 pens each at five barrows or gilts per pen. The barrows and gilts were derived from Yorkshire dams and Duroc-Hampshire sires. Each pen was 3.76 m x 1.83 m and was equipped with two feeders and one nipple drinker. The 18 pens in the barn were randomly allotted to three pST implants: O, 100, or 200 mg of pST. The 200-mg pST implant consisted of two 100-mg pST implants; the same implant, which had a capacity to remain active for 42 d, was used for the duration of the study. According to previously reported studies the in vitro release rate of pST from the 100-mg implant was an average 2.2 mg/d during a 42-d experimental period and 2.40 mg/d during a 35-d experimental period (Azain et al., 1992; Becker et al., 1992). Pigs were allowed ad libitum access to a 20% CP corn-soybean meal diet and had free access to water. On a daily basis, each pig was observed individually for health problems. When pigs reached a weight of |greater than or equal to~95 kg, they were shipped to the University of Guelph Meat Laboratory for slaughter and carcass analysis. The experiment was conducted in the months of August and September; the average time on test was 36.3, 32.3, and 31.1 d for control, 100-, and 200-mg implant groups, respectively. Table 1. Ingredient and nutrient composition of diet Item % Ingredient Corn 64.00 Soybean meal (48% CP) 32.00 Vitamin-mineral premix(a) 4.00 Nutrients, as fed Dry matter 91.18 Digestible energy (calculated), kcal/g 3. 49 Crude protein 20.31 Lysine (calculated) 1.17 Ca .66 P .54 a Contained the follo wing per kilogram of premix: 210 g of Ca, 100 g of P, 120 g of NaCl, 4 g of Fe, 4 g of Zn, 2 g of Mn, 400 mg of Cu, 4 mg of Co, 24 mg of I, 2.24 x |10.sup.5~ IU of vitamin A, 3.2 / |10.sup.4~ IU of vitamin |D.sub.3~, 1,000 IU of vitamin E, 120 mg of vitamin K, 800 |mu~g of vitamin |B.sub.12~, 160 mg of riboflavin, 800 mg of d-pantothenic acid, 900 mg of niacin, 8 g of choline, 20 mg of folic acid, 32 mg of thiamine, 64 mg of pyridoxine, 3.2 mg of biotin, and 9 |mu~g of Se. Measurements. Feed intake and body weights were recorded weekly. Maximum and minimum daily ambient temperatures in the barn were recorded each morning through the duration of the experiment. On arrival at the meat laboratory, pigs were held for |is greater than~2 h before they were electrically stunned and exsanguinated. At slaughter, carcass, head, tail, feet, kidney, and leaf fat weights were recorded. Longissimus muscle depth, fat thickness, and carcass length were also measured and recorded. Carcasses were chilled at 2|degrees~C overnight, after which one-half of each carcass was separated into rough primal cuts and weighed. The primal cuts were trimmed and dissected into lean, fat, skin, and bone and weights were recorded. The structure and color of lean from the loin were subjectively evaluated using a five-point scale as outlined in Agriculture Canada (1986). The belly was graded by using methods proposed by D. C. Smith (National Hog Farmer, 1973) with modification. Objective meat color measurement was done electronically using a Minolta CP-200 Color Meter (Minolta, Industrial Meter Div., Ramsey, NJ). Analyses. The diet fed to the pigs during the experiment was sampled from the feeder each week and analyzed for proximate chemical composition, calcium, and phosphorus (AOAC, 1984). Loin and belly were frozen, ground, and freeze-dried. Lyophilized samples were ground and analyzed for fat using ether extraction (AOAC, 1984). The GLM (SAS, 1985) procedure was used in data analysis. There was no sex (gilts and barrows) x pST interaction; thus, only the main effects of sex and pST implants are reported. Means of pST treatment were compared using a protected LSD test as outlined by Snedecor and Cochran (1980). For the carcass and growth measures, the experimental unit was the individual pig. Results and Discussion The main effects of pST implant and sex on growth rate, feed intake, and feed:gain are summarized in Table 2. Growth rate was not affected (P |is greater than~ .05) by the use of long-term pST implants of 100 or 200 mg. There was a 15% reduction in daily feed consumption by pigs that received the 200-mg pST implant compared with pigs that received the 0-mg pST implant (2.78 vs 2.34 kg/d), and this difference was statistically significant (P |is less than~ .05). The use of long-term pST implants improved (P |is less than~ .05) feed conversion, resulting in a 22% reduction in feed:gain ratio when the 0-mg implant was compared with the 200-mg pST implant. High levels of feed intake during the finishing phase of growth are commonly associated with accelerated fat accretion and a deterioration of feed:gain ratio (Campbell and Taverner, 1985). Repartitioning of energy by pST should lead to an improvement in feed:gain ratio because less energy from the diet is required to deposit 1 kg of lean than is required for 1 kg of adipose tissue accretion. The 22% reduction in feed:gain ratio elicited by the use of a long-term pST implant in the present study is similar in magnitude to those previously reported for pigs that received daily pST injections (Etherton et al., 1986, 1987; Campbell et al., 1989b) but considerably lower than the 60% reduction in feed:gain ratio reported by Smith and Kasson (1990). The 60% reduction in feed:gain ratio was obtained by pigs that gained relatively more slowly (750 g/d) with a poorer feed:gain ratio (4 kg feed/kg gain) while they received daily injections of TABULAR DATA OMITTED 120 |mu~g of pST/kg of BW (approximately 385 mg of pST over the duration of the experiment). In contrast, in the present experiment, pigs gained 850 g/d with 3.2 kg feed/kg gain and received a 200-mg pST implant over the duration of the experiment. Contrary to the reported improvement in ADG elicited by daily injection of pST (Etherton et al., 1986, 1987; Campbell et al., 1989a,b; Smith and Kasson, 1990; Bidanel et al., 1991; Evans et al., 1991), the use of long-term pST implants in the present experiment did not detectably alter growth rate. The absence of improvement in ADG probably results from the dose of pST for the specific weight group of pigs used and the kinetics of pST release from the implant. Of the initial 90 pigs, two gilts, one each from the 100- and 200-mg pST implant groups, did not complete the trial. One gilt died during the 1st wk of treatment and was diagnosed with hemorrhagic bowel syndrome; the other gilt was diagnosed with myopathy-malignant hyperthermia. Daily injections of pituitary and recombinant pST have been reported to be related in certain situations to development of stomach ulcers and(or) death of growing pigs and lactating sows (Machlin, 1972; McLaren et al., 1990; Smith et al., 1991). The results from postmortem examination, however, showed that the death of both gilts was not related to the pST administration in this experiment. Barrows gained faster (P |is less than~ .05) than gilts during the study. The 13% increase in growth rate of barrows over gilts arose almost exclusively from the 18% higher (P |is less than~ .05) feed consumption of barrows compared with gilts. Again, higher levels of feed intake during the finishing phase of growth were accompanied by increased fat deposition and, as a consequence, a higher feed:gain ratio. There was no sex x pST treatment interaction in this study. This is consistent with the results reported by Kraft et al. (1986) and McLaren et al. (1990), who also found no interactions between sex (barrows or gilts) and daily pST injection. Campbell et al. (1989a) observed a significant interaction between sex (boars or gilts) and daily pST injections; the pST offset sex differences for gain:feed ratio and body composition. Hot and cold carcass weights were reduced (P |is less than~ .05) in pigs that received pST implants compared to the control pigs; however, carcass length was similar across treatments. Smith and Kasson (1990) also observed a significant reduction in carcass weight of pigs that received daily injection of pST. The reduction in dressing percentage is partly due to the increase in heart, liver, and kidney weights (Campbell et al., 1989b; Bidanel et al., 1991) and also the pST-induced increase in lungs, stomach, small intestine, and blood weights (Bidanel et al., 1991). Also in agreement with the similarity carcass length among pST implants, Campbell et al. (1989b) observed no difference in carcass length between control pigs and those that received daily injection of 100 |mu~g kg of BW. Becker et al. (1992), however, found that the carcass length was increased in pigs that received a 100-mg rpST implant. It might be possible that differing results on carcass length from various studies are due to the different breeds used and the different stages at which pST administration was commenced. Implantation with 200 mg of pST resulted in a 25% reduction (P |is less than~ .05) in last rib fat compared with 0 mg of pST. There was also a pST-induced reduction in leaf fat. The magnitude of this reduction in fat as a result of pST administration is consistent with partitioning effects of pST. Adipose tissue accretion is a function of the relative rates of lipolysis and lipogenesis. Results from in vivo studies indicate that pST potentiates catecholamine-induced adipose tissue lipolysis (Boyd and Bauman, 1989). In vitro studies have shown that pST reduces basal rates of lipogenesis (Walton et al., 1987) and antagonizes the stimulating effects of insulin on porcine adipose tissue lipogenesis (Walton et al., 1986). The results of this study regarding a reduction in body fat concur with these findings. The use of long-term pST implants increased (P |is less than~ .05) kidney weight. Chung et al. (1985) observed that daily administration of 22 |mu~g of pST/kg of BW to 32-kg pigs for 30 d increased organ weights, TABULAR DATA OMITTED including liver, heart, and kidneys. Histopathological examination of these organs indicated no deleterious effects of pST administration on animal health (Chung et al., 1985). Administration of 70 |mu~g of pST/kg of BW to 40-kg pigs (Etherton et al., 1987) or 100 |mu~g of pST/kg of BW to 60-kg pigs (Campbell et al., 1989b) also induced kidney hypertrophy. The increase in organ weights in pST-treated pigs is partly responsible for the reduction in dressed carcass weight. There was no effect of sex on most carcass or fat measurements. However, longissimus muscle depth was greater (P |is less than~ .05) in gilts than in barrows. Longissimus muscle area was not measured TABULAR DATA OMITTED in this experiment. However, there is a high correlation between longissimus muscle depth and longissimus muscle area (r = .688, unpublished data, C. Haworth, University of Guelph, personal communication). The main effects of long-term pST implants and sex on the weights of wholesale cuts are presented in Table 4. There was no effect of pST implant or sex on any of the wholesale cuts listed in Table 4 except belly weights, for which pST implant resulted in a reduction (P |is less than~ .05), and barrows had lower (P |is less than~ .05) belly weight than gilts. Although there was a tendency for lower wholesale cuts of the ham and loin with pST-implanted TABULAR DATA OMITTED pigs, presumably due to lower (P |is less than~ .05) carcass weights, the trend did not approach statistical significance. Using heavier pigs (102 to 136 kg), McNamara et al. (1991) observed that daily administration of 1.5, 3, 6, or 9 mg of pST/d did not have any effect on weight of ham, loin, or shoulder but reduced belly weight. The most pronounced effects of repartitioning agents, including pST, reported to date have been changes in carcass composition (Etherton et al., 1987; Adeola, 1989; Boyd and Bauman, 1989; Campbell et al., 1989a,b; Bidanel et al., 1991; McNamara et al., 1991). In broad terms, administration of pST to pigs results in increased carcass protein and reduced carcass lipid. In the present experiment, dissected skin and fat from loin, ham, and picnic were affected by pST implant. The use of long-term pST implants resulted in a 16% reduction (P |is less than~ .05) in weight of skin and fat separated from the ham. This finding once again reinforces that pST is capable of reducing fat in highly priced cuts of pork and presents the consumer with a leaner product. There was a 22% reduction (P |is less than~ .05) in weight of skin and fat separated from the loin of pigs implanted with 200 mg of pST compared with pigs that received 0 mg of pST. These results are consistent with those obtained from a recent study in which a 14 to 34% reduction in trimmed ham and loin fat were obtained from pigs injected with 3 or 6 mg of pST/d from 102 to 136 kg of live weight compared with pigs that received 0 mg of pST/d (McNamara et al., 1991). Even though there was a 13% reduction in weight of skin and fat separated from the butt from pigs that received the 100- or 200-mg pST implant, the variation associated with the measurement precluded the detection of statistical significance. There TABULAR DATA OMITTED was also a 13% reduction in the weight of picnic skin and fat in pigs that received the 200-mg implant compared with the 0-mg pST implant. The stimulatory and inhibitory effects of pST on lipolysis and lipogenesis, respectively, as discussed earlier, are expected to contribute to the pST-induced reduction in weights of skin and fat separated from ham, loin, butt, and picnic. Bones and cartilage separated from ham, butt, and picnic were increased (P |is less than~ .05) with pST implant. These 14 to 26% increases in bone and cartilage weights from these prime cuts parallel reported effects of daily injections of pST on chemically analyzed ash (Campbell et al., 1989a; McNamara et al., 1991). Total carcass ash was increased (P |is less than~ .05) by 12% in pigs that received daily injections of 100 |mu~g of pST/kg (Campbell et al., 1989a). In a more recent study using heavier pigs (102 to 136 kg), McNamara et al. (1991) observed a 22% increase in analyzed ash of the loin of pigs that received daily injections of 9 mg of pST. These increases in ash content from the different studies may have an implication for mineral requirements (particularly Ca and P, which are the most abundant in bone) of pigs treated with pST. It has also been reported that iron concentration in bone is higher in pST-treated pigs than in control pigs (Caperna et al., 1989). The weight of lean separated from ham, loin, butt, and picnic were not affected by treatment with pST implants. The reduction in carcass fat of pigs treated with pST has led to the concern that the quality of meat produced by such pigs will be adversely affected. Both subjective and objective measures of meat color were not different in pigs that received 0-, 100-, or 200-mg pST implants. In addition, pST administration did not affect the structure of meat. These observations are consistent with previous reports (Beermann et al., 1990; McNamara et al., 1991). There was no significant effect of pST implant on belly trim, skin, and carcass grade. Ether-extractable fat in longissimus muscle and belly confirmed the lower separable fat (Table 5) in pigs that received pST implants. Implications Long-term implants of porcine somatotropin reduced feed intake and feed:gain ratio in pigs raised from 70 to 100 kg live weight. Pigs that received the porcine somatotropin implants had reduced leaf and rib fat. The implant altered the partitioning of nutrients, and therefore body composition, to an extent similar to that achieved by daily injections. The efficacy of the long-term implants relative to daily injections in reducing feed:gain ratio and carcass fat could be significant if porcine somatotropin is approved for commercial use. Literature Cited Adeola, O. 1989. Muscle and adipose tissue metabolism in pigs. Ph.D. Thesis. Univ. of Guelph, Guelph, ON, Canada. Agriculture Canada. 1986. Pork quality: A guide to understanding color and structure of pork muscle. Agriculture Canada Publ. #5180/B. Ottawa, ON. AOAC. 1984. Official Methods of Analysis (14th Ed.). Association of Official Analytical Chemists, Washington, DC. Azain, M. J., K. D. Bullock, T. R. Kasser, and J. J. Veenhuizen. 1992. Relationship of mode of porcine somatotropin administration and dietary fat to the growth performance and carcass characteristics of finishing pigs. J. Anim. Sci. 70:3086. Becker, B. A., C. D. Knight, F. C. Buonomo, G. W. Jesse, H. B. Hedrick, and C. A. Baile. 1992. Effect of a hot environment on performance, carcass characteristics, and blood hormones and metabolites of pigs treated with porcine somatotropin. J. Anim. Sci. 70:2732. Beermann, D. H., V. K. Fishell, K. Roneker, R. D. Boyd, G. Armbruster, and L. Souza. 1990. Dose-response relationships between porcine somatotropin, muscle composition, muscle fiber characteristics and pork quality. J. Anim. Sci. 68:2690. Bidanel, J.-P., M. Bonneau, A. Pointillart, J. Gruand, J. Mourot, and I. Demade. 1991. Effects of exogenous porcine somatotropin (pST) administration on growth performance, carcass traits, and pork meat quality of Meishan, Pietrain and crossbred gilts. J. Anim. Sci. 69:3511. Boyd, R. D., and D. E. Bauman. 1989. Mechanisms of action for somatotropin in growth. In: D. R. Campion, G. J. Hausman, and R. J. Martin (Ed.) Current Concepts of Animal Growth Regulation. pp 257-293. Plenum Publishing, New York. Campbell, R. G., N. C. Steele, T. J. Caperna, J. P. McMurtry, M. B. Solomon, and A. D. Mitchell. 1989a. Interrelationships between sex and exogenous growth hormone administration on performance, body composition and protein and fat accretion of growing pigs. J. Anim. Sci. 67:177. Campbell, R. G., N. C. Steele, T. J. Caperna, J. P. McMurtry, M. B. Solomon, and A. D. Mitchell. 1989b. Effects of exogenous porcine growth hormone administration between 30 and 60 kilograms on the subsequent and overall performance of pigs grown to 90 kilograms. J. Anim. Sci. 67:1265. Campbell, R. G., and M. R. Taverner. 1985. Effects of strain and sex on protein and energy metabolism in growing pigs. In: P. W. Moe, H. F. Tyrrell, and P. J. Reynolds (Ed.) Energy Metabolism of Farm Animals. pp 78-81. Eur. Assoc. Anim. Prod. Publ. No. 32., Rowman and Littlefield, Totowa, NJ. Caperna, T. J., R. G. Campbell, and N. C. Steele. 1989. Interrelationships of exogenous porcine growth hormone administration and feed intake level affecting various tissue levels of iron, copper, zinc and bone calcium of growing pigs. J. Anim. Sci. 67:654. Chung, C. S., T. D. Etherton, and J. P. Wiggins. 1985. Stimulation of swine growth by porcine growth hormone. J. Anim. Sci. 60:118. Etherton, T. D., J. P. Wiggins, C. S. Chung, C. M. Evock, J. F. Rebhun, and P. E. Walton. 1986. Stimulation of pig growth performance by porcine growth hormone and growth hormone-releasing factor. J. Anim. Sci. 63:1389. Etherton, T. D., J. P. Wiggins, C. M. Evock, C. S. Chung, J. F. Rebhun, P. E. Walton, and N. C. Steele. 1987. Stimulation of pig growth performance by porcine growth hormone: Determination of the dose-response relationship. J. Anim. Sci. 64:433. Evans, F. D., V. R. Osborne, N. M. Evans, J. R. Morris, and R. R. Hacker. 1991. Effect of different patterns of administration of recombinant porcine somatotropin on growth performance and economic returns of pigs in the starter vs. finisher phases of production. Can. J. Anim. Sci. 71:355. Kraft, L. A., D. R. Haines, and R. L. DeLay. 1986. The effects of daily injections of recombinant porcine growth hormone (rpGH) on growth, feed efficiency, carcass composition and selected metabolic and hormonal parameters in finishing swine. J. Anim. Sci. 63 (Suppl. 1):218 (Abstr.). Machlin, L. J. 1972. Effect of porcine growth hormone on growth and carcass composition of the pig. J. Anim. Sci. 35:794. McLaren, D. G., P. J. Bechtel, G. L. Grebner, J. Novakofski, F. K. McKeith, R. W. Jones, R. H. Dalrymple, and R. A. Easter 1990. Dose response in growth of pigs injected daily with porcine somatotropin from 57 to 103 kilograms. J. Anim. Sci. 68:640. McNamara, J. P., C. J. Brekke, R. W. Jones, and R. H. Dalrymple. 1991. Recombinant porcine somatotropin alters performance and carcass characteristics of heavyweight swine and swine fed alternative feedstuffs. J. Anim. Sci. 69:2273. National Hog Farmer. 1973. Consumers say 80% of bacon unacceptable. 18(5):45. SAS. 1985 SAS User's Guide: Statistics. SAS Inst. Inc., Cary, NC. Smith, V. G., and C. W. Kasson. 1990. Growth performance and carcass characteristics of pigs administered recombinant porcine somatotropin during 30 to 110 kilogram live weight. J. Anim Sci. 68:4109. Smith, V. G., A. D. Leman, W. J. Seaman, and F. VanRavenswaay. 1991. Pig weaning weight and changes in hematology and blood chemistry of sows injected with recombinant porcine somatotropin during lactation. J. Anim. Sci. 69:3501. Snedecor, G. W., and W. G. Cochran. 1980. Statistical Methods. (7th Ed.). Iowa State University Press, Ames. Walton, P. E., T. D. Etherton, and C. S. Chung. 1987. Exogenous pituitary and recombinant growth hormones induce insulin and insulin-like growth factor I resistance in pig adipose tissue. Domest. Anim. Endocrinol. 4(3):183. Walton, P. E., T. D. Etherton, and C. M. Evock. 1986. Antagonism of insulin action and in cultured pig adipose tissue by pituitary and recombinant porcine growth hormone: Potentiation by hydrocortisone. Endocrinology 118:2577.

The effect of dose and mode of delivery of recombinant bovine (rbST) or porcine somatotropin (rpST) on the growth rate of female rats with intact pituitaries was investigated in a series of experiments. The overall objective of these studies was to compare the relationship of dose and mode of delivery on the growth response to somatotropin. The equivalence of rbST and rpST in stimulation of growth was demonstrated. In an initial study, treatment of rats with 0, .67 (3 mg/kg), or 2.0 mg/d (9 mg/kg) of rbSt for 28 d resulted in ADG of .8, 2.6, and 3.8 g/d (P < .0001, SEM .1 g). A log-linear dose response to rbST in the range of .07 to 32 mg/d (.3 to 145 mg/kg) for the stimulation of gain was observed. Continuous delivery of rpST in bicarbonate buffer was achieved using osmotic pumps. Sustained, log-linear growth for doses of 0, .5, 1, 2, and 4 mg of rpST/d for 28 d was demonstrated. In a direct comparison of bolus injection and continuous delivery at doses of 0, .22, .67, 2.0, and 6.0 mg of rpST/d, a significant difference in slope (P < .0001) of the modes of delivery was observed; continuous delivery had a greater slope. Depending on the dose administered, bolus injection was either more (< .67 mg/d) or less efficacious (> .67 mg/d) than continuous delivery in its ability to stimulate growth in female rats with intact pituitaries. It is hypothesized that the difference in the slope of the dose-response curves can be accounted for by the animal's ability to utilize the hormone effectively.

Thirty-two crossbred barrows were used to determine the effects of frequency of administration of equivalent total dosages of recombinant porcine somatotropin (rpST) on growth performance, tissue accretion rates, and hormone and metabolite status of pigs. Treatments were control (buffer-injected daily), 60 micron g/kg BW daily (4 injections/4 d), 120 micron g/kg BW injected every other day (2 injections/4 d), or 240 micron g/kg BW given every 4th d (1 injection/4 d). Treatments were initiated at 35 kg BW and continued until each pig had consumed a total of 440 Mcal of DE intake. Pigs were fed a diet that contained 16% CP, 1.2% lysine, and 3.5 Mcal of DE/kg at 85% of calculated ad libitum intake. Feed intake and rpST dose were adjusted at 8-d intervals. The 240 Micron g/kg BW treatment did not decrease appetite beyond the 15% restriction already imposed in the experimental design. Treatment groups responded to rpST in a frequency-dependent manner. Average daily gain was improved by 10, 23, and 36%, respectively, as injection frequency was increased from 1/4 to 2/4 to 4/4 d. Muscle weights were increased uniformly (15% on average) on a BW basis by all rpST treatments. Carcass (21, 42, and 63%), visceral (43, 65, and 112%), and empty body (22, 43, and 65%) protein accretion rates were increased by rpST treatment in a frequency-dependent fashion, respectively. Lipid accretion also was reduced in carcass and empty body (31% on average) by all rpST injection schemes relative to controls; however, visceral lipid accretion was increased by 59% by rpST. Protein utilization efficiency increased linearly by 24, 45, and 65% as the frequency of injection of rpST was increased from 1/4 to 2/4 to 4/4 d. Hormones and metabolites exhibited frequency-related profiles as well. These results suggest that frequency of administration greatly influences the magnitude of responsiveness to rpST and that optimal benefit would be realized by a delivery system that mimicked a daily surge, at minimum, of rpST.

Previous studies have documented the effectiveness of porcine somatotropin (pST) administered by daily injection in promoting lean tissue growth in lean and obese pigs and the influence of sex and genotype. The present study examined the accretive responses in pigs of different lines and sexes to a slow release formulation of pST (pST-SR). Implants that deliver 2.0 mg of pST/d were implanted in genetically lean and obese barrows and gilts at 65 plus or minus .7 kg BW (mean plus or minus SE). Pigs received no, one, or two implants (i.e., doses of 0, 2.0, and 4.0 mg of pST/d). Pigs (four per line x sex x dose) were housed individually and continuously supplied with fresh water and a 19% CP diet containing 1.08% lysine. Pigs were slaughtered on d 0 (four per line x sex) and at the end of the trial (approximately 42 d after implantation) for estimation of initial composition and calculation of accretion rates. Blood samples were collected at d 0, 7, 14, 28, and 42 to measure endocrine and metabolite responses to pST-SR. Sustained-release pST elevated (P < .05) circulating pST throughout the trial with peak concentrations at d 7. On d 7, serum pST concentrations in the pigs given 2.0 mg of pST-SR per day were 16-fold greater than those in control pigs, and in pigs given 4.0 mg of pST-SR per day pST concentrations were 33-fold greater than in controls. Elevated serum pST resulted in increased (P < .05) serum concentrations of insulin-like growth factor (IGF)-I, IGF-II, insulin, and glucose and in reduced (P < .05) concentrations of urea nitrogen and IGF binding protein (IGFBP)-2. Gain was not influenced by pST-SR dose; however, feed consumption was reduced (P < .05) and efficiency of gain was increased (P < .05). Accretion of all body components except cold carcass weight, cecum, and untrimmed Boston butt and ham were changed (P < .05) with pST-SR administration. Heart and stomach were the only components of the carcass and offal whose accretion was not affected by line or sex. Increases in accretion of carcass components (< 75%) induced by sustained-release pST were considerably less than those measured in the organs (liver, 157%; lungs, 748%). The pST-SR treatment resulted in elevated serum concentrations of pST and its mediators and improved efficiency and composition of gain. Thus, pST-SR seems to be an effective method of pST administration; however, the response is influenced by genotype and sex of the treated pig.

The effect of porcine somatotropin (PST) on the lipid profiles of adipose tissue and muscle was investigated. Sixteen crossbred barrows were injected daily with either 3 mg of PST or a placebo. After slaughter, total lipid and fatty acid composition of raw subcutaneous (SC) adipose and intermuscular (IM) adipose tissue and longissimus muscle were determined. The SC adipose tissue from pST-treated pigs had a 7.5% decrease in total lipid content; specific fatty acids 16:0, 18:0, and 18:1(n-9)c decreased most. The IM fat from pST-treated pigs had lower levels of 16:0 and 20:0. There was no effect of PST treatment on the lipid profile of the longissimus muscle. The data suggest that PST treatment produces small but significant changes in the saturated fatty acid content of adipose tissue in pigs. Key Words: Pigs, Somatotropin, Fatty Acids, Lipids, The effects of porcine somatotropin on lipids and fatty acids in subcutaneous and intermuscular adipose tissue and longissimus muscles were studied in sixteen crossbred barrows given daily injections of either porcine somatotropin (pST) or placebo. Results show that pST decreases total lipid content of subcutaneous adipose tissue, reduces saturated fatty acids but does not affect the content of polyunsaturated fatty acids.

Prepubertal gilts of obese (n = 24) or lean (n = 24) genetic lines were injected (s.c.) daily with 0, 2, or 4 mg of porcine somatotropin (pST) for 6 wk starting at 160 d of age to determine whether pST affects follicular function. Blood and ovaries were collected at slaughter 24 h after the last injection. Surface follicles is greater than or equal to 1.0 mm in diameter were counted, and pools of follicular fluid (FFL) and granulosa cells were collected from 1.0- to 3.9-mm (small) and 4.0- to 6.9-mm (medium) follicles. Oocytes were collected from small and medium follicles and evaluated for maturational stage and viability. Porcine somatotropin increased (P < .08) the numbers of small but not the numbers of medium follicles per gilt (P > .10). Oocyte maturation and viability were not affected by pST or genetic line. Porcine somatotropin increased (P < .05) concentrations of insulin-like growth factor I (IGF-I) in serum and FFL of both obese and lean gilts; IGF-I was lower (P < .01) in lean gilts. Treatment with pST decreased (P < .05) IGF-II in FFL of lean but not in that of obese gilts. Dose of pST and line had no effect on concentrations of progesterone in FFL of small or medium follicles or on concentrations of estradiol in FFL of small follicles. Concentrations of estradiol in FFL of medium follicles were decreased (P < .05) by pST (2 and 4 mg/d) in obese gilts, but estradiol was lower (P < .01) and unaffected (P > .10) by pST in lean gilts. The numbers of LH/hCG binding sites in granulosa cells were decreased (P < .05) by pST (4 mg/d) in medium follicles. The 4 mg/d dose of pST increased (P < .05) IGF-I binding protein activity only in serum of obese gilts. We conclude that 2 and(or) 4 mg/d of pST can increase concentrations of IGF-I in serum and FFL and stimulate growth of small follicles in two genetically divergent lines of gilts without affecting oocyte viability.

Ten pigs with an average initial live weight of 65 kg were used to investigate the effects of daily exogenous porcine pituitary growth hormone (pGH; .1 mg center dot kg to the -1 center dot d to the -1) for a 13-d period on N retention and whole-body protein turnover. Feed intake was restricted to both the control (treated with excipient) and pGH-treated groups to ensure that animals in each group consumed equal amounts. Whole-body protein turnover was estimated from the excretion of 15N in urinary urea and ammonia after a single oral dose of (15N)glycine. Nitrogen balance and whole-body N flux were increased by 35 to 40% with pGH treatment (P < .001). Protein synthesis and breakdown were increased by 56 and 59% (P < .001), respectively, in pGH-treated pigs relative to controls. These higher rates of protein turnover seemed to lower slightly the efficiency of the metabolic process for protein deposition. However, the absolute increment in protein synthesis rate was greater than that for breakdown, leading to the increased net N retention. Thus, pGH treatment improved the utilization of dietary amino acids for protein deposition.

Ninety-six pigs were used to investigate the relationship of diet (control vs fat-supplemented with equal energy:protein ratios), porcine somatotropin (pST) administration (non-treated; 2 mg/d, daily injection; and 2 mg/d, 6-wk implant), and sex (barrows and gilts) to performance and carcass characteristics. Diet and pST treatments were initiated at 87 kg of BW and continued for 38 d. Both the fat-supplemented diet (P < .001) and pST treatment (P < .0001) improved feed efficiency. The effects of diet were accounted for by differences in energy density of the diets. Across diets, pST improved gain:feed ratio by 29 and 16% in pigs treated by daily injection and the implant, respectively; the two modes of delivery resulted in different responses (P < .01). Circulating insulin-like growth factor I (IGF-I) levels, determined from blood samples drawn on d 35, were increased 2.5-fold above those of controls in pigs treated by either daily injection or the implant. However, the elevation of glucose and decrease in blood urea nitrogen concentrations in response to pST were of a greater magnitude in pigs treated by daily injection. Similarly, reductions in backfat thickness and the rate of backfat accretion determined by ultrasound were greater in response to the daily injection of pST than in response to the implant. Lean meat ratio, calculated from measurements with a Fat-O-Meater probe, was increased by 6 and 13% by the implant and daily injection, respectively. It is concluded that although the use of an implant that delivers pST on a continuous basis was as effective as the same dose administered as a bolus injection for increasing IGF-I levels, it was less effective in improving feed efficiency and carcass quality.

Forty-eight pigs of three known stress classifications were injected daily with porcine somatotropin (pST; 4 mg/d) or placebo. The effects of pST and stress classification on the sensory, physical and chemical characteristics of loin chops were observed. Chops from pST-treated animals were less tender and juicy than chops from control animals. Positive stress classification also significantly decreased juiciness but had no effect on tenderness and flavor. A significant interaction was observed for initial juiciness and sustained juiciness between chops from pST and stress-positive pigs. Whereas chops from carriers and normal pigs showed a reduction in juiciness traits with the pST treatment, among stress-positive animals both initial and sustained juiciness were increased with pST treatment. Treatment with pST had no effect on the fat, protein, and moisture content of the longissimus muscle. Furthermore, stress classification had no effect on the fat and moisture content of the longissimus muscle, but protein content was significantly higher in loin chops from stress-positive animals. Chops from pST-treated animals had significantly higher maximum shear force values, required more energy to break the sample, and had higher yield point values than chops from control animals, but stress classification did not affect the shear force values significantly. Treatment of stress-susceptible animals with pST does not lead to an increased incidence of pale, soft, exudative meat and may improve juiciness attributes of chops from stress-positive animals. However, pST treatment of animals, in this trial, led to a reduction of juiciness and tenderness of pork loin chops.

The dose-dependent effects of porcine somatotropin (pST) on growth performance and composition of carcass gain were investigated in 150 growing pigs. The experiment involved two genotypes (barrows from the Pig Improvement Company (PIC) and a University of Nebraska (NEB) gene pool line) and two sexes (PIC barrows and boars). At 30 kg, pigs were randomly assigned within each genotype and sex subclass to receive daily i.m. injections of 50, 100, 150, or 200 150 or 200 micrograms of pST/kg BW or an equivalent volume of an excipient. A diet (3.5 Mcal of DE/kg) supplemented with crystalline amino acids and containing 22.5% CP was available on an ad libitum basis until pigs were slaughtered at approximately 90 kg live weight. Excipient-treated PIC barrows exhibited faster and more efficient growth (P < .001) and a higher capacity for carcass protein accretion (P < .001) but similar rates of lipid deposition compared to excipient-treated NEB barrows. Within the PIC genotype, control boars grew at a rate similar to that of barrows, but they were more efficient (P < .05) and deposited more carcass protein (P < .05) and less lipid (P < .001). Carcass protein accretion rate increased (P < .001) up to approximately 150 micro-g of pST center dot kg BW to the -1 center dot d to the -1, whereas lipid deposition decreased (P < .001) with each incremental dose of pST. Although differences between PIC boars and barrows for all criteria were negated with increasing pST dose, they were maintained between the two genotypes. Polynomial regressions suggested that a slightly higher pST dose was required to optimize the feed:gain ratio compared with rate of gain and that the dose (micrograms per kilogram BW per day) was a function of the genotype and sex (feed:gain: 185, 170, and 155; rate of gain: 155, 155, and 125 for NEB barrows, PIC barrows, and PIC boars, respectively).

This study was conducted to determine the effect of daily recombinant porcine somatotropin (rpST) injection (0 or 120 [micro]g/kg BW) and dietary CP level of the feed (14 or 26% CP) on pancreatic characteristics of growing pigs. Daily injection of rpST did not affect pancreatic weight (P = .885) but did decrease pancreatic amylase content (P = .005). The ratios of amylase:protein and amylase:trypsin were also lowered by daily rpST injection (P = .002 and P = .0002, respectively). There were protein x rpST and protein x rpST x sex interactions for the ratio of amylase: chymotrypsin. The CP content of the diet had a greater effect than the injection of rpST on pancreatic characteristics. Pigs consuming the 26% CP diet had significantly higher pancreatic weight (P = .003) and greater total pancreatic chymotrypsin (P = .006) than pigs consuming the 14% CP diet. The ratios of trypsin and chymotrypsin to DNA were also higher in pigs fed the 26% CP diet (P = .007 and P = .005, respectively). These responses were not influenced by sex. Recombinant porcine somatotropin seemed to have a slight effect on porcine pancreatic characteristics; however, dietary protein had a greater effect on pancreatic characteristics in market-weight hogs. Key Words: Somatotropin, Protein, Amylases, Trypsin, Chymotrypsin, Pigs, The effects of daily recombinant porcine somatotropin (rpST) injection and of dietary protein level on the pancreatic characteristics of growing pigs was investigated. The purpose was to determine whether the decreased fat deposition and enhanced feed efficiency of rpST-injected pigs are mediated by changes in pancreatic characters. The results showed that rpST does not have any significant effect on the pancreas. In contrast, dietary protein content had significant effects on the pancreas of growing pigs, manifested in increased weight and chymotrypsin content.

The influence of porcine somatotropin (pST) on the rate of in vivo lipogenesis and glucose kinetics in growing pigs was evaluated by testing for these physiological processes in animals injected with the hormone. Treatment with pST decreases both the inclusion of glucose in fat tissues and the accumulation of fat. This is due to the reduction of lipogenesis, particularly the production of new triglycerides. On the other hand, exogenous insulin heightened the lipogenesis rate by around 50%.

Nonesterified fatty acid (NEFA) and glycerol kinetics in pigs administered with porcine somatotropin (pST) were evaluated to find out the effect of the hormone on fatty acid metabolism. Analysis of the uptake of infused tritium-marked glycerol and oleic acid revealed that a growing pig's lipid catabolism is very low indicating that the pig is in a lipogenic stage. Lipolysis and NEFA kinetics increased with the administration of pST, but not by a considerble amount. Other mechanisms beside lipolysis and NEFA kinetics may be responsible for the reduction of fat accumulation during pST treatment.

The effect of porcine somatotropin (pST) on plasma glucose, insulin, glycerol, nonesterified fatty acids (NEFA) and plasma urea nitrogen (PUN) concentrations was examined. Analysis of blood from pigs receiving intramuscular pST injections revealed that transient hyperglycemia and hyperinsulinemia occurs after injection. Glycerol and NEFA exhibited temporary elevation of concentration, but PUN showed reduced levels. This pattern in the blood metabolite concentrations could be explained by the reduced metabolic activities illicited by pST, which also resulted in the reduction of food intake.