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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

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

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.

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.

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.