Search

Questions regarding the digestive fate of DNA and protein from transgenic feed have been raised in regard to human consumption and commercial trade of animal products (e.g., meat, milk, and eggs) from farm animals fed transgenic crops. Using highly sensitive, well-characterized analytical methods, pork loin samples were analyzed for the presence of fragments of transgenic and endogenous plant DNA and transgenic protein from animals fed meal prepared from conventional or glyphosate-tolerant Roundup Ready (RR) soybeans. Pigs were fed diets containing 24, 19, and 14% RR or conventional soybean meal during grower, early-finisher, and late-finisher phases of growth, respectively, and longissimus muscle samples were collected (12 per treatment) after slaughter. Total DNA was extracted from the samples and analyzed by PCR, followed by Southern blot hybridization for the presence of a 272-bp fragment of the cp4 epsps coding region (encoding the synthetic enzyme 5-enolpyruvylshikimate-3-phosphate synthase derived from Agrobacterium sp. strain CP4) and a 198-bp fragment of the endogenous soybean gene le1 (encoding soy lectin). Using 1 microgram of input DNA per reaction, none of the extracted samples was positive for cp4 epsps or le1 at the limit of detection (LOD) for these PCR/Southern blot assays. The LOD for these assays was shown to be approximately one diploid genome equivalent of RR soybean DNA, even in the presence of 10 micrograms of pork genomic DNA. A 185-bp fragment of the porcine preprolactin (prl) gene, used as a positive control, was amplified from all samples showing that the DNA preparations were amenable to PCR amplification. Using a competitive immunoassay with an LOD of approximately 94 ng of CP4 EPSPS protein/g of pork muscle, neither the CP4 EPSPS protein nor the immunoreactive peptide fragments were detected in loin muscle homogenates from pigs fed RR soybean meal. Taken together, these results show that neither small fragments of transgenic DNA nor immunoreactive fragments of transgenic protein are detectable in loin muscle samples from pigs fed a diet containing RR soybean meal.

An experiment involving 25 experiment stations in the North Central and Southern regions (NCR-42 and S-288, respectively) was conducted to assess the degree of uniformity of diet mixing among stations and to assess the variability among station laboratories in chemical analysis of mixed diets. A fortified corn-soybean meal diet was mixed at each station using a common diet formula (except for vitamin and trace-mineral additions). The diet was calculated to contain 14% crude protein (CP), 0.65% Ca, 0.50% P, and 125 ppm Zn (based on 100 ppm added Zn). After mixing, samples were collected from the initial 5% of feed discharged from the mixer, after 25, 50, and 75% was discharged, and from the final 5% of discharged feed. The five samples were sent to the University of Kentucky, finely ground, and divided into subsamples. Each set of five subsamples from each station was distributed to three randomly selected stations for analysis of CP, Ca, P, and Zn (i.e., each station analyzed five diet sub-samples from three other stations). In addition, two commercial and two station laboratories analyzed composites of the five subsamples from each of the 25 mixed diets. Based on the laboratories that analyzed all diets, means were 13.5, 0.65, and 0.52%, and 115 ppm for CP, Ca, P, and Zn, respectively. Ranges of 11.8 to 14.6% CP, 0.52 to 0.85% Ca, 0.47 to 0.58% P, and 71 to 182 ppm of Zn were found among the 25 diet mixes. The coefficients of variation among the 25 diet samples for CP, Ca, P, and Zn were 4.3, 9.3, 4.1, and 17.4%, and among the 25 laboratories were 3.6, 12.5, 10.7, and 11.1%, respectively. Overall analyses of the five sub samples were, respectively, CP: 13.4, 13.6, 13.4, 13.5, and 13.4% (P < 0.06); Ca: 0.66, 0.67, 0.67, 0.66, and 0.67%; P: 0.50,0.51,0.51,0.50, and 0.50%; and Zn: 115, 116, 112, 113, and 120 ppm (P < 0.001). Diets were not uniformly mixed at all stations (station x sample No. was P < 0.08 for Ca and P < 0.01 for CP, P, and Zn). Among stations, the range of the five samples, expressed as a percentage of the mean and averaged for CP, Ca, P, and Zn, varied from +/- 1.1% (i.e., 98.9 to 101.0%) to +/- 12.9% (84.6 to 110.4%), with an overall average of +/- 5.2%. Neither type nor volume of mixers was related to mixing uniformity. The results suggest that uniformity of diet mixes varies among experiment stations, that some stations miss their targeted levels of nutrients (especially Zn), and that the variability among experiment station laboratories in analysis of dietary Ca, P, and Zn in mixed diets is quite large.

Brewers dried yeast, a source of mannan oligosaccharides (MOS), was assessed as an alternative to an antimicrobial agent (carbadox) for young pigs in two experiments. The yeast contained 5.2% MOS. Agglutination tests confirmed adsorption of several serovars of E. coli and Salmonella spp. onto the yeast product. In Exp. 1, seven replicates (five pigs per pen) of 22-d-old pigs were fed a nonmedicated basal diet or the basal diet with carbadox (55 mg/kg), yeast (3%), or a combination of 3% yeast and 2% citric acid for 28 d. Carbadox did not improve growth performance. Growth rate and feed intake were depressed (P < 0.05) in pigs fed yeast alone or in combination with acid. Log counts of total coliforms, Escherichia coli, and Clostridium perfringens in feces were not affected by diet, but Bifidobacteria spp. counts were lower (P < 0.05) in pigs fed the yeast + acid diet and lactobacilli counts were higher (P < 0.05) in pigs fed yeast. Fecal pH and VFA concentrations and intestinal morphological traits were not consistently affected by diet. Serum IgG levels were elevated in the yeast + acid (P < 0.01) group. In Exp. 2, the effects of yeast and carbadox additions to the diet on enteric microbial populations in young pigs housed in isolation units were evaluated. Pigs (n = 24) were weaned at 11 d of age (4.1 kg BW) and placed in isolation chambers (two pigs per chamber) equipped with individual air filtering systems and excrement containers. Treatments were a nonmedicated basal diet and the basal diet with 55 mg/kg of carbadox or with 3% yeast. Diets were fed for 29 d, then each pig was orally dosed with approximately 9.5 x 10(8) CFU of E. coli K88. Daily fecal E. coli K88 counts were not different (P > 0.05) among treatments, but fecal shedding of carbadox-resistant coliforms was higher (P < 0.01) during the 9-d period in pigs fed carbadox. Total fecal coliforms were consistently lower throughout the postinoculation period in pigs fed yeast (P < 0.05). Yeast reduced colonization oftotal coliforms in the duodenum,jejunum, cecum, and colon, but it did not have a consistent effect on colonization of E. coli K88. Pigs fed yeast tended (P < 0.10) to have higher serum IgG levels than controls. In these experiments, brewers dried yeast and carbadox had minimal effects on growth, microbial populations, and intestinal health traits of early-weaned pigs, but certain serum immunological traits were enhanced by feeding yeast.

This study was conducted to evaluate potential interactive effects of supplemental Cr and dietary protein levels in growing pigs. Thirty-six individually penned barrows, 22 to 63 kg, were used in a 2 x 3 factorial arrangement of supplemental Cr (0 or 200 ppb from chromium tripicolinate) and protein level (76, 83, or 90% of lysine requirement). A corn-soybean meal basal diet was designed to supply all mineral and vitamin needs, 90% of the estimated metabolizable energy need, and 76% of the estimated protein need at 70% of ad libitum feed intake. Additional protein to 83 or 90% of the lysine requirement was provided by a soy protein isolate supplement. Growth data were collected for a 50-d period, and pigs were killed at a mean of 63 kg BW. Increasing lysine levels linearly (P < 0.01) increased ADG and liver weight. Lysine level had a quadratic effect on 10th rib backfat thickness (P < 0.05) and cooler shrink (P < 0.01) with the highest responses at the 83% lysine level. Increasing lysine level linearly decreased (P < 0.05) carcass content of ash and lipid and quadratically increased the carcass water content (P < 0.01). Carcass accretion rate showed a linear increase for protein (P < 0.01) and water accretion (P < 0.01). Dry matter composition of the longissimus muscle showed linear increases of ash (P < 0.05) and protein (P < 0.01) and a linear decrease of lipid content (P < 0.01) resulting in a linear increase (P < 0.05) of the protein to lipid ratio based on the increasing lysine levels. Pre-feeding insulin levels were increased (P < 0.05) with increasing level of lysine. One hour post-feeding, a quadratic lysine response for plasma glucose (P < 0.05) was observed with the lowest concentration at 83% lysine. Cr addition increased 10th rib backfat thickness (P < 0.10). There was no Cr x lysine level interaction (P > 0.10) observed for any of the growth or carcass traits. Plasma glucose concentrations pre-feeding were lower for Cr-supplemented pigs (P < 0.01). As expected, increasing protein levels in protein-deficient diets increased protein accretion while decreasing lipid accretion in 22 to 63 kg growing pigs; however, these effects were more clearly seen in the longissimus muscle than in the entire carcass. Supplementation of Cr exerted only minor effects with few Cr x lysine interactions observed in this study.

Dehulled soybean meal prepared from genetically modified, herbicide (glyphosate)-tolerant Roundup Ready soybeans containing the CP4 EPSPS protein and near-isogenic conventional soybeans were assessed in an experiment with growing-finishing pigs. The soybeans were grown in the yr 2000 under similar agronomic conditions except that the Roundup Ready soybeans were sprayed with Roundup herbicide. Both were processed at the same plant. The composition of the two types of soybeans and the processed soybean meal were similar. Corn-soybean meal diets containing conventional or Roundup Ready soybean meal and fortified with minerals and vitamins were fed to 100 cross-bred pigs from 24 to 111 kg BW. Diets contained approximately 0.95% lysine initially and were reduced to 0.80 and 0.65% lysine when pigs reached 55 and 87 kg BW, respectively. There were 10 pens (five pens of barrows and five pens of gilts) per treatment with five pigs per pen. All pigs were scanned at 107 kg mean BW and all barrows were killed at the end of the test for carcass measurements and tissue collection. Rate and efficiency of weight gain, scanned backfat and longissimus area, and calculated carcass lean percentage were not different (P > 0.05) for pigs fed diets containing conventional or Roundup Ready soybean meal. Gilts gained slower, but they were more efficient and leaner (P < 0.05) than barrows. Responses to the type of soybean meal were similar for the two sexes with no evidence of a diet x sex interaction for any of the traits. In most instances, carcass traits of barrows were similar for the two types of soybean meal. Longissimus muscle samples from barrows fed conventional soybean meal tended (P = 0.06) to have less fat than those fed Roundup Ready soybean meal, but water, protein, and ash were similar. Sensory scores of cooked longissimus muscles were not influenced (P > 0.05) by diet. The results indicate that Roundup Ready soybean meal is essentially equivalent in composition and nutritional value to conventional soybean meal for growing-finishing pigs.

A total of 36 gilts were used to assess the effects of Cr tripicolinate supplementation on immune response in sows and their offspring during the periparturient and neonatal period. Gilts were raised from weaning to reproductive age on diets with either 0 (-Cr) or 200 (+Cr) ppb supplemental Cr from CrPic. Subsequently, 22 gilts (9 -Cr and 13 +Cr) in parity 1 and 16 sows in parity 2 (7 -Cr and 9 +Cr) underwent immune status testing. Only sows that completed all procedures in parity 1 were included in parity 2. Sows were immunized with ovalbumin about 3 wk (d 0), and again 14 d later for gilts, prior to anticipated farrowing, and serum was collected on d 0 and at 14-d intervals for a total of four samples. Serum was collected from five to six pigs/litter at 24 h after birth, three or six pigs/litter the day after weaning (25 d of age) in parity 1, and three pigs/litter the day of weaning (20 d of age) in parity 2. Milk was collected at 1 h (colostrum), 6.5 d (early), and 19 d (late) after farrowing. The only effect of Cr on total immunoglobulin (Ig) concentration was on sow serum IgG (21.7 and 24.1 mg/mL for -Cr and +Cr, respectively; P = 0.08) and IgM (11.0 and 12.5 mg/mL; P = 0.06) on d 0. No effect (P > 0.15) of Cr was observed on the IgG antibody response to ovalbumin, but Cr was associated (P < 0.10) with a decreased IgM antibody response to ovalbumin beginning on d 14. In parity 2, colostral total IgG increased (80.6 and 92.4 mg/mL for parity 1 and 2, respectively; P = 0.06), which was reflected in the neonates at 24 h after birth (33.6 and 39.7 mg/mL; P = 0.01) and at weaning (7.3 and 13.3 mg/mL; P < 0.001). Supplementation of Cr tripicolinate had minimal effects on humoral antibody response of the dam or its transfer to the neonate; however, parity greatly influenced the concentrations of immunoglobulins in the milk and their transfer to the neonate.

A total of 60 pigs from 15 litters were used during two experiments to assess the effects of maternal supplementation of Cr tripicolinate on performance and immune status of the offspring during the first 42 d after weaning. Gilts were raised on diets with either 0 (-Cr) or 200 (+Cr) ppb supplemental Cr from Cr tripicolinate. Their offspring were weaned at about 23 d of age. Pigs from dams fed supplemental Cr were fed Cr-supplemented diets after weaning and pigs from unsupplemented dams were not fed supplemental Cr. Pigs were housed in groups of three according to litter origin (six -Cr and nine +Cr) and BW. Feed and water were available for ad libitum consumption. Serum was collected 24 h after birth, the day after weaning (d 0), and, subsequently, every 7 d through d 28 for measurement of total immunoglobulin (Ig) G and IgM. For the 42-d nursery period, ADG (511 and 531 g/d for -Cr and +Cr, respectively), ADFI (827 and 851 g/d), and gain:feed (0.62 and 0.62) were not affected (P > 0.15) by Cr. Total IgG was not affected (P > 0.10) by Cr on d 0 (7.6 and 7.7 mg/mL for -Cr and +Cr, respectively) or on d 7 (6.3 and 6.1 mg/mL for -Cr and +Cr, respectively), when the lowest concentrations were observed. By d 28, total IgG had risen (11.7 and 8.9 mg/mL for -Cr and +Cr, respectively) and was affected by Cr (P = 0.03). Total IgM followed a similar pattern and was lowest on d 7. In each trial, IgG at 24 h after birth was inversely related to IgG from d 14 through 28 in the nursery. Additionally, the lowest Ig concentrations occurred between 4 and 5 wk of age, rather than at weaning (23 d of age); this may represent a vulnerable period for weanling pigs. Supplementation of the weanling pig diets with Cr tripicolinate did not significantly affect performance and immune status during the postweaning period.

Two experiments were conducted to evaluate potential interactive effects of supplemental Cr and dietary energy supply in growing pigs. Experiment 1 used 36 individually penned barrows, 25 to 65 kg, in a 2 x 3 factorial arrangement of supplemental Cr (0 or 200 ppb) and energy level (70, 80, or 90% of ME requirement). A corn-soybean meal basal diet was designed to supply all protein, mineral, and vitamin needs and 70% of the estimated ME need at 70% of ad libitum feed intake. Additional energy to 80% or 90% of the ME requirement was provided by a cornstarch/corn oil blend. In Exp. 2, 30 individually penned barrows, 23 to 68 kg, were used in a 2 x 4 factorial arrangement of supplemental Cr (0 or 200 ppb) and added energy source (none, cornstarch, corn oil, or choice white grease) with basal diets identical to Exp. 1. The various energy sources were added to 90% of the ME requirement. In both experiments, growth data were collected over a 50-d period and pigs were killed at 70.1 kg. Increasing energy levels increased (linear, P < 0.01) ADG, average backfat thickness, 10th rib backfat thickness, and cooler shrink and decreased (linear, P < 0.01) longissimus muscle area in Exp. 1. Carcass composition increased (linear, P < 0.01) in lipid and decreased in protein, water, and protein:lipid ratio in response to increasing ME levels. Similar results were observed in Exp. 2 in response to added energy, regardless of the energy source used. In response to ME, linear increases (P < 0.05) in plasma insulin concentration before feeding and after feeding were observed in Exp. 1. In Exp. 2, plasma insulin concentration was lower for the basal diet before feeding (P < 0.05) and higher for the starch diet after feeding (P < 0.01); insulin:glucose ratio increased (P < 0.01) after feeding for starch compared to oil and fat. No consistent effect of Cr or Cr x ME level on performance or carcass was observed (P > 0.10) in these experiments. Similarly, no Cr effect or Cr x ME interaction (P > 0.10) was observed in plasma glucose or insulin levels. Dietary energy levels markedly affected growth criteria in growing pigs (23 to 68 kg) in these experiments, as anticipated, but supplemental Cr was without effect on performance or carcass responses.

Ileally cannulated pigs were used to assess the effects of four dietary levels of microbial phytase (Natuphos) on the apparent and true digestibility of Ca, P, CP, and AA in dehulled soybean meal. Fourteen pigs (25 kg initial BW) were surgically fitted with T-cannulas at the terminal ileum and assigned to diets in a replicated 7 x 7 Latin square design. Following a 14-d recovery, four diets consisting of 30.5% soybean meal with 0, 500, 1,000, or 1,500 units of phytase/kg of diet were fed. Diets 5 (1.05% lysine, 0.90% Ca, and 0.75% P) and 6 (1.05% lysine, 0.90% Ca, and 0.75% P) contained 35.25% soybean meal and 27.0% soy protein concentrate, respectively. Diet 7 (0.37% lysine, 0.03% Ca, and 0.05% P) was a low-CP, casein-based diet used to estimate the nonspecific endogenous losses of Ca, P, CP, and AA in order to estimate the true digestibility of these nutrients. All diets contained cornstarch and dextrose and were fortified with vitamins and minerals. Chromic oxide was used as an indigestible indicator. The diets were fed daily at 9% of metabolic BW (BW0.75). Apparent and true ileal digestibility of P increased quadratically (P < 0.01) and true digestibility of Ca increased linearly (P < 0.07) with increasing levels of phytase. Apparent digestibility of Ca was unaffected (P = 0.15) by phytase level. Apparent and true ileal digestibility of CP and most AA increased slightly with the addition of 500 units of phytase/kg of diet, but not at higher levels of phytase supplementation (in most cases, cubic effect, P < 0.05). Apparent and true ileal nutrient digestibility coefficients were unaffected by soybean meal source (Diet 1 vs Diet 5), except for arginine and Ca. The apparent and true digestibility coefficients for most of the AA tended (P < 0.10) to be lower in diets containing soy protein concentrate vs the common source of soybean meal used in Diet 5, but ileal digestibilities of Ca and P were unaffected (P = 0.15). In this study, supplemental microbial phytase did not improve the utilization of AA provided by soybean meal but was an effective means of improving Ca and P utilization by growing swine fed soybean meal-based diets.

A study involving nine research stations from the NCR-42 Swine Nutrition Committee used a total of 1,978 crossbred pigs to evaluate the effects of dietary ZnO concentrations with or without an antibacterial agent on postweaning pig performance. In Exp. 1, seven stations (IA, MI, MN, MO, NE, ND, and OH) evaluated the efficacy of ZnO when fed to nursery pigs at 0, 500, 1,000, 2,000, or 3,000 mg Zn/kg for a 28-d postweaning period. A randomized complete block experiment was conducted in 24 replicates using a total of 1,060 pigs. Pigs were bled at the 28-d period and plasma was analyzed for Zn and Cu. Because two stations weaned pigs at < 15 d (six replicates) and five stations at > 20 d (18 replicates) of age, the two sets of data were analyzed separately. The early-weaned pig group had greater (P < 0.05) gains, feed intakes, and gain:feed ratios for the 28-d postweaning period as dietary ZnO concentration increased. Later-weaned pigs also had increased (P < 0.01) gains and feed intakes as the dietary ZnO concentration increased. Responses for both weanling pig groups seemed to reach a plateau at 2,000 mg Zn/kg. Plasma Zn concentrations quadratically increased (P < 0.01) and plasma Cu concentrations quadratically decreased (P < 0.01) when ZnO concentrations were > 1,000 mg Zn/kg. Experiment 2 was conducted at seven stations (KY, MI, MO, NE, ND, OH, and OK) and evaluated the efficacy of an antibacterial agent (carbadox) in combination with added ZnO. The experiment was a 2 x 3 factorial arrangement in a randomized complete block design conducted in a total of 20 replicates. Carbadox was added at 0 or 55 mg/kg diet, and ZnO was added at 0, 1,500, or 3,000 mg Zn/ kg. A total of 918 pigs were weaned at an average 19.7 d of age. For the 28-d postweaning period, gains (P < 0.01), feed intakes (P < 0.05), and gain:feed ratios (P < 0.05) increased when dietary ZnO concentrations increased and when carbadox was added. These responses occurred in an additive manner. The results of these studies suggest that supplemental ZnO at 1,500 to 2,000 mg Zn/kg Zn improved postweaning pig performance, and its combination with an antibacterial agent resulted in additional performance improvements.

A cooperative research study was conducted by members of a regional committee (North Central Regional Committee on Swine Nutrition [NCR-42]) to assess the variability in nutrient composition (DM, CP, Ca, P, Se, NDF, and amino acids) of 14 sources of wheat middlings from 13 states (mostly in the Midwest). A second objective was to assess the analytical variability in nutrient assays among 20 laboratories (labs; 14 experiment station labs and six commercial labs). Wheat middlings were obtained from each participating station's feed mill. The bulk density of the middlings ranged from 289 to 365 g/L. The number of labs that analyzed samples were as follows: DM and CP, 20; Ca, 16; P, 15; Se, 7; NDF, 10; and amino acids, 9. Each lab used its own analytical procedures. The middlings averaged 89.6% DM, 16.2% CP, .12% Ca, .97% P, 36.9% NDF, .53 mg/kg Se, .66% lysine, .19% tryptophan, .54% threonine, .25% methionine, .34% cystine, .50% isoleucine, and .73% valine. As expected, there was considerable variation in nutrient composition among the 14 sources (P < .01), especially for Ca (.08 to .30%) and Se (.05 to 1.07 mg/kg). "Heavy" middlings (high bulk density, >335 g/L), having a greater proportion of flour attached to the bran, were lower in CP, lysine, P, and NDF than "light" middlings (<310 g/L), having cleaner bran, resulting in negative correlations between bulk density and CP (r = -.61), lysine (r = -.59), P (r = -.54), and NDF (r = -.81). Each 1-percentage-point increase in CP in the wheat middlings was associated with .0235 (r2 = .61) and 2.1 (r2 = .39)-percentage-point increases in lysine and NDF, respectively. Lysine content was associated with NDF, CP, and bulk density of wheat middlings (r2 = .88). There was considerable variation among laboratories (P < .01) in analysis of all nutrients. The CV among sources (100 x sigmaS/mean) was greater than among labs (100 x sigmaL/mean) for CP, Ca, P, Se, and NDF, but the CV among labs was greater than that among sources for DM and all of the amino acids except lysine and phenylalanine.

A cooperative research study involving 635 gilts was conducted at eight research stations to further estimate the lysine requirement of finishing gilts. Dietary crude protein levels of the five dietary treatments ranged from 16.0 to 24.4% with calculated lysine levels of .80, .95, 1.10, 1.25, or 1.40%. Each station contributed a minimum of two replicate pens of pigs per treatment. Average initial and final weights were 53.6 and 116.4 kg, respectively. At the end of the experimental period, pigs were killed and hot carcass weight, 10th-rib fat depth, and longissimus muscle area were measured. Carcass fat-free lean percentage and fat-free lean gain were estimated from these data. Daily lysine intakes averaged 21.8, 25.9, 30.5, 34.3, and 37.8 g/d for the five treatment groups, respectively. Increasing the dietary lysine from .80 to .95% numerically increased weight gain and gain:feed, but these increases were not maintained at higher levels of dietary lysine. Overall, rate and efficiency of gain decreased (cubic, P < .01) with increasing dietary lysine. Carcasses were leaner at the two higher levels of dietary lysine as evidenced by reduced 10th rib backfat (linear, P < .01), increased longissimus area (quadratic, P < .04), and increased percentage of estimated fat-free lean (linear, P < .01). Carcass fat-free lean gain was not influenced by dietary lysine except for a small numerical improvement (P < .11) at the .95% level of dietary lysine that paralleled the improvement in body weight gain. The results indicate that the dietary lysine requirement of finishing gilts with a mean carcass fat-free lean growth rate of 306 g/d from 54 to 116 kg body weight is probably no higher than .80% of the diet to achieve maximum rate and efficiency of body weight gain and carcass lean growth rate. The results also indicate that higher dietary lysine levels may increase carcass leanness in finishing gilts, possibly due to reduced intake of NE. Whether this response is due to the effects of lysine alone, protein (i.e., other amino acids), or soybean meal is unknown.

An experiment was conducted to determine the effect of high dietary intakes of Zn and Cu and their combination on growth performance of weanling pigs with diverse health status and management strategies. Twelve experiment stations cooperated and used a total of 1,356 pigs that averaged 6.55 kg BW and 22.2 d age at weaning. The four dietary treatments, all of which met or exceeded NRC requirements, were 1) control, 2) 3,000 ppm Zn (from Zn oxide), 3) 250 Cu ppm (from Cu sulfate), or 4) 3,000 ppm Zn and 250 ppm Cu. The diets were fed as a complex Phase I diet (1.4% lysine) for 7 d followed by a Phase II diet (1.2% lysine) for 21 d. Chlortetracycline (220 ppm) was added to all diets. Fecal color (1 = yellow to 5 = black) and consistency (1 = very firm to 5 = very watery) were scored daily for 3 wk. At the end of the 28-d study, 412 pigs were bled at five stations, and plasma Cu, Zn, and Fe concentrations were determined at one station with atomic absorption spectrophotometry. Average daily gain (375, 422, 409, 415 g/d), feed intake (637, 690, 671, 681 g/d), and gain/feed (586, 611, 611, 612 g/kg) were improved (P < .01) by the addition of Zn and(or) Cu. Significant Cu x Zn interactions imply that the responses to Zn and Cu were independent and not additive. There were significant (P < .01) Zn and Cu effects and a Zn x Cu interaction on fecal color (3.17, 3.24, 4.32, 3.57) and consistency (2.39, 2.14, 2.14, 2.13). Dietary additions of Cu and Zn resulted in elevated plasma concentrations of Cu and Zn, respectively. These data indicate that pharmacological additions of 3,000 ppm Zn (oxide) or 250 ppm Cu (sulfate) stimulate growth beyond that derived from intakes of Zn and Cu that meet nutrient requirements. However, the combination of Zn and Cu did not result in an additive growth response.

Weanling pigs were used in a series of studies to determine the feeding value of an enzymatically digested protein product developed from a blend of swine and poultry abattoir by-products. The initial study used 156 pigs weaned at approximately 22 d of age to compare the product with menhaden fish meal in Phase II diets. The product supported equal growth rate, and there was no preference for diet exhibited based on inclusion level of the enzymatically digested protein product. The second study used 100 pigs weaned at approximately 21 d of age to compare the product with spray-dried animal blood cells in Phase II diets. The product supported a growth rate equal to that with the blood cells, and the combination of products enhanced growth rate (P<.05). The third study used 265 pigs to compare the product with spray-dried porcine plasma in a slope ratio growth assay. Results demonstrated a relative feeding value of 91% for the product over a 4-wk feeding period. The fourth study used 290 pigs to compare the product with spray-dried porcine plasma in Phase II diets; results demonstrated comparable growth performance. The final study used 180 pigs to compare the product with spray-dried porcine plasma in Phase I diets; results demonstrated comparable growth performance. These data indicate that the enzymatically digested abattoir by-product is a high-quality protein source for weanling pigs.

A cooperative research study involving members of a regional committee (North Central Regional Committee on Swine Nutrition [NCR-42]) was conducted to assess the variability in nutrient composition (DM, CP, Ca, P, Se, and amino acids) of corn and soybean meal from 16 sources (15 states, mostly in the Midwest) and to assess the analytical variability in nutrient assays among 22 laboratories (labs; 16 experiment station labs and six commercial labs). Corn samples were obtained from each participating station's feed mill during a 3-yr period (1989, 1990, and 1992), as were soybean meal samples during a 2-yr period (1989 and 1990). Both regular soybean meal (with hulls) and dehulled soybean meal were represented in the study. Samples were analyzed for DM and CP by all 22 labs, for Ca and P by 15 labs, for amino acids by 10 labs, and for Se by 6 labs. Each lab used its own analytical procedures. Samples of corn and soybean meal varied in their nutrient composition depending on the area of origin. The greatest variation among sources was in Se concentration, ranging from .02 to .29 mg/kg in corn and .08 to .95 mg/kg in soybean meal. Crude protein and lysine in corn were positively correlated, but the regression coefficient was low (r2 = .49). The relationship between CP and lysine for the two soybean meals combined was considerably stronger (r2 = .81). Lysine in corn increased by .018 percentage point and lysine in soybean meal (regular and dehulled combined) increased by .063 percentage point for each 1 percentage point increase in CP. Except for CP and Se, the analytical variability among labs was as great as, and in some cases greater than, the variability in nutrient composition among sources of corn and soybean meal. Within-lab analytical variability tended to be less than among-lab variability. Some labs performed certain analyses with considerably less variability and more accuracy than others.

Six sets of four littermate barrows initially averaging 75.5 kg BW were equally fed (within blocks) fortified corn-soybean meal diets (1.30% lysine) containing two concentrations of Ca (.50 and 1.00%) and P (.45% and .90%) in a 34-d test. One-half of the pigs were injected with 4 mg of porcine ST (pST)/d. Following a 7-d adjustment period, total collection of feces and urine was performed during two periods (d 1 to 10 and d 20 to 30) for the determination of Ca and P apparent digestibility (absorption) and retention. Pigs were bled after each period (d 10, 20, and 30) for the determination of serum metabolites associated with Ca, P, and bone metabolism. Feed intake for the 30-d period averaged 2,020 g/d. There were no treatment x period interactions, so the absorption and retention data were pooled across periods. The absorption and retention of Ca and P were greater (P<.01) in pigs fed the higher Ca and P levels. Within each Ca and P level, pST reduced (P<.01) fecal Ca and P excretion. Administration of pST did not affect urinary P excretion, but it increased (P<.03) urinary Ca excretion in pigs fed the low-Ca diet. The absorption and retention of Ca and P were increased (P<.01) by pST; however, the increases in Ca retention and P absorption and retention on an absolute basis (g/d) were more pronounced in pST-treated pigs consuming the higher Ca and P diet (interaction, P<.10). Serum concentrations of 1,25-dihydroxyvitamin D3, osteocalcin, and IGF-I on d 10 and 30 were increased (P<.07) with pST administration. However, the increases in 1,25-dihydroxyvitamin D3 and osteocalcin in pST-treated pigs were more pronounced when the lower dietary Ca and P levels were fed (interaction, P<.08). Urinary excretion of hydroxyproline increased (P<.01) with pST administration, but this effect was more pronounced in pST-treated pigs fed the lower Ca and P diet (interaction, P<.09). These results suggest that pST increases the absorption and retention of Ca and P independent of dietary Ca and P level. However, serum measures associated with Ca, P, and bone metabolism in pST-treated pigs were dependent on the Ca and P content of the diet, suggesting an effect of pST on the homeostatic control of Ca, P, and bone metabolism.

We conducted two experiments to determine whether the efficacy of chromium picolinate (CrP) on growth performance, carcass composition, and tissue accretion rates is dependent on the lean gain potential of the pigs. In Exp. 1, 40 barrows (20 from each of two genetic backgrounds; two pigs per pen, five pens per treatment) were fed a fortified, corn-soybean meal basal diet (.95% lysine from 19 to 55 kg BW; .80% lysine from 55 to 109 kg BW) without or with 200 microg/kg of Cr from CrP. The addition of Cr had no effect on performance, carcass measurements, or accretion rates of carcass protein or lipid, regardless of the lean gain potential of the pigs. In Exp. 2, 60 group-penned pigs (three pigs per pen; five pens per treatment) were fed a fortified, corn-soybean meal basal diet without or with 200 microg/kg of Cr from CrP from 21 to 104 kg BW. Within the dietary Cr treatments, half of the pigs received daily injections of 3 mg of porcine somatotropin (pST) from 54 to 104 kg BW. The pST administration resulted in faster growth rates (P < .007), improved feed efficiency (P < .001), increased longissimus area (P < .001), and decreased 10th-rib backfat (P < .001). Administration of pST also increased the percentage and accretion rate of carcass protein (P < .001) and decreased the percentage and accretion rate of carcass lipid (P < .001). The addition of CrP to the diet had no effect on any variable measured in either the untreated or pST-treated pigs. In these studies, Cr was ineffective at altering the composition of the carcass and its effects were not dependent on the pig's potential for lean gain.

Carnosine (β-alanine-L-histidine) and anserine (β-alanine-1-methyl histidine) are endogenous antioxidants found in skeletal muscle. The objective of this research was to determine if supplementation of swine diets with histidine (histidine; 0.40%) and/or β-alanine (β-alanine; 0.225%) was an effective method to increase carnosine and anserine concentrations and the oxidative stability of Longissimus dorsi (LD) and Vastus intermedius (VI) muscles. Dietary treatments had no effect on carnosine and anserine concentrations in LD; however, histidine + β-alanine supplementation increased carnosine and anserine in VI muscle compared to β-alanine supplementation. Dietary supplementation had no effect on the formation of thiobarbituric acid reactive (TBARS) or lipid peroxides in cooked VI and LD. In salted VI and LD muscle, differences in TBARS and peroxides were observed; however, these differences did not consistently correlate with differences in anserine and carnosine concentrations. Therefore, the results of this research suggest that supplementation of swine diets with β-alanine and/or histidine is not an efficient method to increase the oxidative stability of pork.

A regional study involving a total of 618 nursery pigs with 468 continuing through the grower-finisher period evaluated the feeding duration of a Phase 1 starter diet (1, 2, or 3 wk) to 23-d old weanling pigs of two weaning weights (5.5 or 7.5 kg). The study was a 3 x 2 factorial arrangement of treatments in a randomized complete block design conducted in 19 replicates during the nursery period, with 14 replicates continuing through the grower-finisher period. Upon completion of feeding the Phase 1 diet for the experimental period, pigs were fed a Phase 2 diet (total of 5 wk for both Phases), whereupon a corn-soybean meal mixture formulated to .80% lysine was fed during the grower (to 56 kg BW) and a .65% lysine diet to a final body weight of 105 kg. Station effects were significant (P < .05) but station x treatment responses were not (P > .15). Pigs with heavier weaning weights gained faster (P < .01) and consumed more feed (P < .01) during each week of the nursery period. Nursery pig gains (P < .06) and gain: feed ratios improved (P < .01) when the Phase 1 diet had been fed for either 2 or 3 wk for both pig weight groups. There was no interaction response during the nursery period between weaning weight or duration of feeding the Phase 1 diet on daily gains or feed intake measurements; however, pigs in the heavier weight group were more efficient (P < .05) in feed utilization when fed the Phase 1 diet for 2 or 3 wk. During the grower-finisher period, gains were higher (P < .01) with the heavier pig group. When the Phase 1 diet had been fed for either 2 or 3 wk to the pigs of either weight group, gains (P < .01) and feed efficiency (P < .05) were improved. There was no evidence of compensatory growth for the lower weight pig group during the subsequent grower or finisher periods. Pigs with heavier weaning weights reached 105 kg BW approximately 8 d sooner (P < .01) and consumed less total feed (P < .05) from weaning to 105 kg than those in the lower weight group. Feeding the Phase 1 diet for 2 wk to pigs of either weight group reduced the time from weaning to 105 kg BW, but weaning heavier pigs seemed to have a greater effect on postweaning performance than the feeding duration of a Phase 1 diet.

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.

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 < .01) but consumed less feed than untreated pigs (P < .01). Increasing the dietary P level improved most of the bone traits. Administration of pST reduced (P < .01) MM strength and percentage ash in the MM and femurs, but it increased (P < .01) femur diameter and wall thickness. Bone strength and percentage ash were reduced in pST-treated pigs fed low dietary P; however, at higher dietary P, these traits were similar to or greater than those in untreated pigs (pST x P, P < .10). Generally, bone traits in pST-treated pigs reached a plateau at higher dietary P concentrations and at higher P intakes compared with those in untreated pigs. These results indicate that pST administration increases the dietary P level that is required to maximize bone traits in finishing pigs.

We conducted three 28-d experiments involving a total of 915 pigs to assess the relative efficacy of tribasic Cu chloride (Cu2[OH]3Cl) and Cu sulfate pentahydrate (CuSO4.5H20) in diets for weanling pigs. Experiments 1 and 2 were conducted at an experiment station (University of Kentucky), and Exp. 3 was conducted at a commercial feed company's swine research facilities (United Feeds, Inc.). The basal diet was a fortified corn-soybean meal-dried whey diet (1.25% lysine) with no antimicrobials in Exp. 1 or with carbadox (55 mg/kg) in Exp. 2 and 3. In Exp. 1, 135 pigs were weaned at 27 to 31 d and fed the basal diet without or with 100 or 200 ppm Cu from Cu chloride, or 100 or 200 ppm Cu from Cu sulfate from 7.9 to 17.7 kg BW. The 200 ppm level of Cu from Cu sulfate improved ADG (P < .10), and both levels of Cu from Cu chloride tended to improve feed:gain. In Exp. 2, 150 pigs were weaned at 27 to 31 d and fed the basal diet without or with 100, 150, or 200 ppm Cu from Cu chloride, or 200 ppm Cu from Cu sulfate from 8.9 to 20.8 kg BW. Addition of 200 ppm Cu improved ADG (P < .08) and ADFI (P < .01), but not feed:gain. Source of Cu did not affect performance. In Exp. 3, 630 pigs were weaned at 16 to 20 d and fed a common diet for 10 to 12 d until the start of the experimental period. The same experimental diets as used in Exp. 2 were fed from 9.1 to 25.5 kg BW. Both Cu sources improved ADG (P < .01), and sources and levels of Cu did not differ. Liver Cu increased in pigs fed 200 ppm Cu, and Cu sulfate tended to increase liver Cu more than did Cu chloride in one experiment, but not in another experiment. The results indicate that tribasic Cu chloride is as effective as Cu sulfate in improving growth in weanling pigs.

A total of 576 d-old, male, broiler chicks were used in two trials 1) to determine the range of Ca and P levels over which the response in bone characteristics is linear and 2) to determine the influence of particle size of defluorinated rock phosphate (DFP) on the bioavailability of Ca and P in DFP. Six treatments were used in Experiment 1 in which varying percentages of added Ca (.00, .06, .12, .24, .36, and .48%) and added P (.00, .05, .10, .20, .30, and .40%) were evaluated in a corn-soybean meal diet containing 23% CP, .47% Ca, and .39% P (.14% available P). Weight gain, feed intake, and tibia breaking strength increased (P less than .001) with increasing levels of dietary Ca and P. Treatments in Experiment 2 consisted of: 1) Diet 1, a corn-soybean meal basal diet (23% CP, .50% Ca, .46% P, .21% available P), 2) Diet 1 with .12% added Ca from calcium carbonate (CC) and .07% added P from monosodium phosphate (MSP), 3) Diet 1 with .24% added Ca from CC and .14% added P from MSP; and 4 to 8), Diet 1 with .24% added Ca and .14% added P from five particle sizes of DFP. Feed intake, weight gain, and tibia breaking strength and ash percentage increased linearly (P less than .01) and feed:gain ratio decreased quadratically (P less than .10) with increasing percentages of added Ca and P in Diets 1 to 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of estradiol benzoate and prostaglandin F(2alpha) (PGF(2alpha)) on concentrations of progesterone and estrogen in serum and the percentage of live births were determined in 21 gilts treated with exogenous progesterone in late gestation. All gilts received progesterone (25mg s.c. four times daily) from Days 108 through 113 of gestation. Gilts receiving no other treatments (controls) had elevated levels of progesterone through 1800 h on Day 114 (29.2 +/- 11.4 ng/ml) and farrowed at 115.6 +/- 0.3 d of gestation with a relatively low percentage of live births (66.8 +/- 17.3). Gilts treated with PGF(2alpha) administered at 0600 h on Day 114 had less (P<0.01) progesterone by 1800 h (7.0 +/- 1.3 ng/ml) relative to that of the controls, but they had similar gestation lengths (115.5 +/- 0.3) and percentages of live births (50.0 +/- 16.2). Administration of estradiol benzoate (10 mg) to gilts at 0600 h on Day 114 did not reduce progesterone on Day 114 or the gestation length relative to that of the control gilts, but it did increase (P<0.05) the percentage of live births (100%).

Three trials were conducted with 252 pigs to determine the effects of the dietary additions of Cu (250 ppm as copper sulfate), with and without sulfide (500 ppm as ferrous sulfide), and antibiotics (55 ppm chlortetracycline or 27.5 ppm virginiamycin) on the performance and liver Cu stores of growing-finishing pigs. Single additions of Cu, chlortetracycline or virginiamycin to a 16% protein, corn-soybean meal-based diet improved daily gains by 4.0, 4.2 and 3.4% and feed to gain ratios by .3, 2.9, and 1.3%, respectively, in comparison with those of pigs fed the control diet. The addition of ferrous sulfide to the high Cu diets reduced liver Cu stores from 278 to 21 ppm, a level approaching that of the control pigs, and increased the growth response to supplemental Cu by 4.0%. The inclusion of both Cu and an antibiotic in the diet in the in the absence or presence of sulfide resulted in daily gains in feed to gain ratios similar to those of pigs receiving a single antimicrobial agent. These data suggest that the growth-promoting effects of Cu and chlortetracycline or Cu and virginiamycin are not additive in the growing-finishing pig allowed to consume feed ad libitum.

Swine from two herds with different histories of antibiotic exposure were fed diets containing 0 or 55 mg of chlortetracycline (CTC)/kg. One of five pigs in each herd-diet treatment group was infected orally with Escherichia coli strain BEL15R that was resistant to nalidixic acid (NA), chloramphenicol (C), streptomycin (S), sulfamethizole (TH) and tetracycline (TE). Effects of CTC on the quantity and duration of fecal shedding of E. coli BEL15R and on the transmission of strain BEL15R and its R-100 plasmid from infected pigs to uninfected pigs and chicks were determined. Quantity and duration of shedding were greater in infected antibiotic-herd pigs than in infected nonantibiotic-herd pigs. Feeding on CTC increased the duration of shedding in infected pigs from both herds. Strain BEL15R colonized and was shed in one uninfected antibiotic pig in each treatment group, but it did not colonize in any of the uninfected nonantibiotic-herd pigs or in the uninfected chicks. In vivo transfer of resistance to C, S, TH and TE occurred in the infected antibiotic-herd pigs but not in the infected nonantibiotic-herd pigs. Transfer of the R-100 plasmid occurred from the infected to the uninfected antibiotic-herd pigs and to the uninfected chicks housed near the antibiotic-herd pigs fed CTC, but not to the chicks housed with the antibiotic-herd pigs fed the control diet. No transfer of resistance occurred from the infected nonantibiotic-herd pigs fed either CTC or control diet.

Chlortetracycline (CTC) resistance in anaerobic and coliform bacteria was examined in the large intestines of two groups of growing pigs that had received antibiotic-free diets since weaning. One group of pigs was from a low resistance herd (LR) that had not received antibiotics for 8 yr, while the other group of pigs was from a high resistance herd (HR) that routinely received antibiotics. After a 20-d adjustment period in a common production facility, LR pigs on an antibiotic-free diet had lower proportions of anaerobes (27%) and coliforms (22%) that were resistant to 25 micrograms CTC/ml than did similarly fed HR pigs (81 and 48%, respectively). Continued maintenance of LR and HR pigs on the antibiotic-free diet in a common production facility tended to increase resistance in anaerobes and coliforms from LR pigs to levels comparable with those in HR pigs at the end of an 85-d feeding trial, but not after 14 d. Administration of CTC in the feed at therapeutic (220 micrograms/g for 14 d) and growth-promoting (27.5 micrograms/g for 85 d) levels markedly increased percentages of resistant anaerobes and coliforms in LR pigs, but not in HR pigs after 14 d. Similar antibiotic effects were not seen at the end of the 85-d trial. These data demonstrate that, while exposure to antibiotics in feed may increase resistance in intestinal populations, other factors such as environment, cross-contamination and herd history can also influence the observed level of antibiotic resistance in swine.

Two experiments involving 1,020 litters were conducted at eight research stations to determine the effects of dietary NaCl (salt) concentration during gestation and lactation on reproductive performance of sows. Primiparous and multiparous sows were fed fortified corn- or grain sorghum-soybean meal diets at 1.82 kg/d during gestation. During the winter months (December, January, February) the feeding level was increased to 2.27 kg/d. Sows had ad libitum access to diets during lactation. Dietary concentrations of added salt were .50 and .25% in Exp. 1 and .25 and .125% in Exp. 2. When more feed was fed during gestation, the salt concentrations were reduced to .40, .20, .20 and .10%, respectively, in order to maintain a constant daily intake of Na and Cl during gestation. Gestation weight gain and lactation (21-d) weight loss of the sows were not affected by dietary salt level in either experiment. In Exp. 1, lowering the salt concentration did not influence the number of pigs farrowed, but it resulted in a .05 kg/pig reduction (P less than .01) in average birth weight. Average 21-d pig weights also tended (P less than .19) to be lower in the low-salt group. There was a decrease in litter size from the first to the second farrowing for sows fed low salt, but not for sows fed the higher salt concentration. In Exp. 2, reducing the salt content from .25 to .125% did not alter reproductive performance. The overall ratio of males to females at birth in the population of greater than 10(4) pigs was 52.3:47.7. Lower salt intakes tended to reduce the percentage of males born in both experiments, although the differences were not significant (P greater than .3). The results indicate that reducing the salt concentration in sows diets from .50 to .25 or .125% reduces birth weight in newborn pigs. When continued for more than one reproductive cycle, feeding less than .5% salt appears to reduce litter size at birth and weaning.

Twelve pregnant gilts were assigned to three treatments (four gilts per treatment): (1) corn oil (control) injected subcutaneously four times daily from day 110 of gestation until onset of lactation; (2) 25 mg progesterone (P4) injected subcutaneously four times daily from day 110 of gestation through day 113, or (3) 25 mg P4 injected subcutaneously from day 110 through day 115 of gestation. Excluding one gilt on treatment 2 which farrowed on day 110, average lengths of gestation for control gilts and gilts receiving treatments 2 and 3 were 113.3 +/- 1.2 (SE), 115.6 +/- .7 and 118.0 +/- .4 days. Associated mean percentages of live births were 87.4 +/- 5.9, 48.8 +/- 24.4 and 2.5 +/- 2.5, respectively. P4 averaged 2.9 +/- .6 ng/ml in blood serum of control gilts during the 24 hr preceding parturition. P4 was released in a sporadic pattern by gilts on treatment 3, resulting in higher P4 concentrations (9.0 +/- 1.7 ng/ml) for the same prepartum period. Concentrations of P4 in serum of gilts on treatment 2 averaged 7.6 +/- 1.6 ng/ml, intermediate to, but not different from, concentrations of P4 in controls and gilts on treatment 3. Concentrations of estrogen in serum of control gilts averaged 6.2 +/- 1.3 ng/ml during the 24 hr preceding parturition, whereas concentrations of estrogen in gilts treated with P4 were reduced (P less than .01) to below 2 ng/ml during the same prepartum period. The erratic pattern of concentration of P4 during and after administration of exogenous P4 may reflect a disturbance of the secretion or metabolism of endogenous P4. We suggest that failure to suppress P4 post-treatment plus reduced estrogenic stimulation impedes the birth process and contributes to the high incidence of stillbirths observed in gilts with progestin-delayed parturition.

Multiple resistance and antibiotic resistance were examined in coliforms isolated at slaughter from the large intestines of two groups of growing pigs that had received antibiotic-free diets since weaning. One group of pigs was from an antibiotic-fed (AB) herd that routinely received chlortetracycline (CTC) in feed, while the other group was from a nonantibiotic-fed (NAB) herd that had not received antibiotics for 8 yr. After a 20-d adjustment period in a common production facility, the mean number of antibiotics in the resistant pattern of isolates from NAB pigs was found to be lower (P less than .05) than that in isolates from AB pigs. The proportions of isolates resistant to ampicillin, kanamycin, neomycin, penicillin, streptomycin and sulfamethizole were lower (P less than .05) in NAB pigs than in AB pigs. Similar herd differences were not observed after pigs from both herds were maintained in a common production facility on an antibiotic-free diet for 105 d. Oral administration of CTC at therapeutic (220 micrograms/g of diet) and at subtherapeutic (27.5 micrograms/g) levels for 14 d increased (P less than .05) the mean numbers of antibiotics in the resistance patterns of isolates from NAB pigs, but did not alter multiple resistance in isolates from AB pigs. After 14 d, subtherapeutic CTC increased the percentage of isolates resistant to ampicillin, kanamycin, penicillin, streptomycin, tetracycline and sulfamethizole, while therapeutic CTC only increased the percentage of isolates from NAB pigs resistant to penicillin, tetracycline and sulfamethizole. Similar antibiotic effects were not seen in isolates from AB pigs after 14 d and were not seen in isolates from either group of pigs at the end of an 85-d feeding trial.