Influence of porcine somatotropin on the phosphorus requirement of finishing pigs: I. Performance and bone characteristics

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.     

Time course of increased plasma cytokines, cortisol, and urea nitrogen in pigs following intraperitoneal injection of lipopolysaccharide

The emerging view is that reduced feed intake, lean muscle accretion, and growth in immunologically challenged pigs is the result of increased cytokine activity, but this has not been directly tested. To begin addressing this issue, 72 crossbred barrows and gilts (11.55 +/- .19 kg BW) were not fed for 12 h and then injected i.p. with 0, .5, or 5 micrograms/kg of Escherichia coli lipopolysaccharide (LPS). Blood was collected by jugular puncture at 0, 2, 4, 8, 12, and 24 h after injection. Plasma levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), cortisol, plasma urea nitrogen (PUN), NEFA, and triglycerides were determined. Immunological stress was induced by LPS as indicated by increased secretion of TNF-alpha, IL-6, and cortisol. In pigs receiving 5 micrograms/kg of LPS, plasma TNF-alpha was increased 10-fold at 2 h after injection and was still elevated (P < .01) at 4 h. In these same pigs, plasma concentration of IL-6 was increased at 2 h and peaked at 4 h with levels exceeding baseline values by 200-fold (P < .01). Cortisol was elevated at 2, 4, and 8 h after injection (P < .01). The increased secretion of cytokines and cortisol in pigs injected with 5 micrograms/kg of LPS was followed by an increase in protein degradation, as evidenced by PUN values that were increased two- and threefold at 8 and 12 h after injection, respectively. However, unlike previous reports in laboratory animal species, plasma glucose, NEFA, and triglycerides were not altered by LPS. Nonetheless, as the period of feed deprivation progressed from 12 to 36 h, plasma NEFA and triglycerides increased (P < .05) and plasma glucose tended to decrease. We believe that immunological challenge induces cytokine synthesis and secretion in swine which, in turn, may induce protein catabolism.     

Lipopolysaccharide-induced reductions in body weight gain and feed intake do not reduce the efficiency of arginine utilization for whole-body protein accretion in the chick

The effects of repeated injections of 400 microg Escherichia coli lipopolysaccharide (LPS) on chick performance from 11 to 22 d posthatching were examined in chicks fed casein-based diets containing graded levels of arginine. Administration of LPS reduced (P < 0.05) weight gain, feed intake, and protein accretion, and there was a tendency (P=0.07) for LPS administration to be more growth-depressing at the higher than at the lower levels of supplemental arginine. Regression analysis of protein accretion for the first three doses of arginine indicated that protein accretion was a linear (P < 0.01) function of supplemental arginine intake for both saline-injected (r2=0.94) and LPS-injected (r2=0.93) chicks. Slopes of the best-fit regression lines for both treatment groups were equal, indicating that arginine utilization for protein accretion was not affected by LPS administration. The dietary arginine concentration required to maximize weight gain and feed efficiency was unaffected by LPS administration, with both saline- and LPS-injected chicks reaching plateaus in weight gain and feed efficiency at 0.90 and 0.98% digestible arginine, respectively.     

Porcine somatotropin (pST) increases IGF-I mRNA abundance in liver and subcutaneous adipose tissue but not in skeletal muscle of growing pigs

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 (approximately 60 kg BW) were allotted to four treatment groups (n = 5) and treated with either 0, 35, 70, or 140 micrograms/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 micrograms of total RNA, IGF-I mRNA levels were highest in s.c. adipose tissue. Levels of IGF-I mRNA were 1.9-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.     

Transcranial Doppler sonography in the pre- intra- and post-operative evaluation of 85 patients undergoing carotid endarterectomy

Porcine somatotropin (pST) administration reduces the sensitivity of pigs to insulin, and after several days of treatment, it alters baseline circulating concentrations of pST, insulin, glucose, and other metabolites. The length of time required to develop this reduction in whole-body insulin sensitivity has not been established. To investigate this, eight castrate pigs received daily injections of either recombinant pST (120 micrograms/kg BW) or exicipient. Intravenous insulin tolerance tests (1.0 microgram/kg BW) were done before the first pST injection (Day 0) and on Day 1, 3, 5, and 8 of pST treatment. Control animals had insulin tolerance tests on Day 0 and again on Day 8 of treatment. By Day 8, the glucose response to the insulin tolerance tests in pST-treated pigs was 45% of the response of the control group (P < 0.01). Glucose response areas between Day 1, 3, 5, and 8 of pST treatment were not different (P > 0.10). The maximum effect of pST on glucose response to insulin was achieved by Day 1. Therefore, factors responsible for the development of reduced whole-body insulin sensitivity in pST-treated pigs are fully expressed within 21 hr of the initial pST treatment.     

Enhancement of the insulin antagonistic effect of porcine somatotropin in swine using a monoclonal antibody

A monoclonal antibody (mAb), PS-7.6, to porcine somatotropin (pST) significantly enhanced the growth responses to pST injections in hypophysectomized (hypox) rats but could not be tested in pigs because of the large quantity of antibody required for a growth trial. Because pST inhibits the hypoglycemic effects of insulin, an insulin tolerance test procedure was established to measure pST activity in jugular-catheterized pigs. Doses of 0, 30, 100, and 300 micrograms/kg per day of pST were split and administered subcutaneously (sc) in equal portions twice daily for 2 d. After a 17-hr fast, plasma samples were obtained at 10-min intervals for 30 min before an intravenous injection of insulin (0.08 IU/kg) and then for an additional 50 min. Because pST increased fasting plasma glucose concentrations, preinsulin glucose values were used as a covariate to adjust the postinsulin concentrations. pST caused a dose-dependent increase in resistance to the insulin injection in these pigs. The areas under the curves (AUC), for plasma glucose were 22.1, 29.0, 39.0, and 47.2 mg/dl per min for the 0, 30, 100, and 300 micrograms/kg pST doses, respectively. Because different doses of pST could be detected, the PS-7.6 enhancement of pST treatment was evaluated. In the first experiment, five pigs/group each received sc injections of either vehicle, pST (75 micrograms/kg; approximately 3.0 mg/d), pST (75 micrograms/kg) + PS-7.6 at 3.75 mg/kg, or pST (75 micrograms/kg) + PS-7.6 at 15 mg/kg for 2 d before the insulin test. The pST and PS-7.6 were combined and incubated for at least 1 hr at room temperature before being injected. The injection of pST alone did not significantly change insulin tolerance activity (23.1 vs. 21.1, AUC), but insulin resistance was enhanced when this dose of pST also included PS-7.6 (27.4 and 29.5, AUC, respectively; P < 0.05). In a second experiment, the effects of PS-7.6 and PS-4.2, a mAb that did not potentiate the pST-stimulated growth of hypox rats, were compared. The five pigs/treatment received either vehicle, pST (75 micrograms/kg), pST (75 micrograms/kg) + PS-7.6 (3.75 mg/kg), or pST (75 micrograms/kg) + PS-4.2 (3.75 mg/kg) for 2 d. The administration of pST increased the resistance to insulin (26.7 vs. 18.8, AUC; P < 0.01), which was markedly potentiated by PS-7.6 (54.3, AUC, P < 0.001) but not affected by PS-4.2 (27.6 AUC). The injection of PS-7.6 at 7.5 mg/kg without exogenous pST did not alter the sensitivity to insulin. These results indicate that PS-7.6, but not PS-4.2, enhanced the insulin antagonistic activity of pST in swine, suggesting that an enhancement of pST-stimulated growth would also occur in PS-7.6-treated pigs.     

An evaluation of ruminally degradable intake protein and metabolizable amino acid requirements of feedlot calves

Ruminally degradable intake protein (DIP) and metabolizable indispensable amino acid (MIAA) requirements of feedlot steers were evaluated. Dietary treatments consisted of isocaloric 80% concentrate steam-flaked corn-based diets containing either .8% urea, 1.5% fish meal (FM), 3.0% FM, 4.5% FM, or 4.5% soybean meal (SBM). Treatment effects on characteristics of ruminal and total tract digestion were evaluated using four Holstein steers (249 kg) with cannulas in the rumen and proximal duodenum. Ruminal digestibility of OM (RDOM; P < .05) and feed N (P < .01) and microbial N flow (MNF; P < .01) to the small intestine were greater with urea as the supplemental N source. The level of DIP was closely associated (R2 = .89) with MNF. Postruminal digestibility of OM was greater (P < .05) for FM than for urea-supplemented diets, compensating for lower RDOM. There were no treatment effects (P > .10) on DOM. As the level of FM was increased, MIAA increased linearly (P < .01). Intestinal MIAA were similar (P > .10) for urea- and SBM-supplemented diets. Treatment effects on 56-d growth performance were evaluated using 100 medium-framed crossbred steers (231 kg). Daily weight gain (linear effect; P < .01), DM intake (linear effect; P < .10), feed efficiency (linear effect; P < .05), and diet NE (linear effect; P < .05) increased with level of FM supplementation. Daily weight gain (P < .10) and DM intake (P < .05) were greater for urea- than for SBM-supplemented diets. Using bovine tissue as the reference protein, the biological value (based on chemical score) of the intestinal chyme protein averaged 73%; methionine was first-limiting. There was a close association (R2 = .99) between methionine supply to the small intestine and observed/expected dietary NE. The metabolizable methionine requirement (MMETR, g/d) of medium-framed feedlot steers can be reliably predicted from measures of BW and ADG (MMETR = 1.565 + .0234ADG[268 - (29.4 x .0557BW(.75)ADG(1.097))/ADG] + .0896BW(.75)). There was a very close association (R2 = .89) between DIP and MNF (MNF = 13.7DIP - .66DIP(2) + 25.9). At maximal observed synthesis, DIP accounted for 76% of the MNF. A minimum of 100 g DIP/kg of total tract digestible OM was required to maximize RDOM and MNF.     

Influence of lipopolysaccharide-induced immune challenge and diet complexity on growth performance and acute-phase protein production in segregated early-weaned pigs

Segregated early-weaned pigs (initially 4.0 kg and 14 +/- 1.5 d of age) were used to quantify the effects of lipopolysaccharide (LPS)-induced immune challenge and nursery diet complexity (complex, medium, and simple) on growth performance and haptoglobin production. Three treatments of immune challenge consisted of pigs given ad libitum access to feed (control), challenged with LPS and given ad libitum access to feed (LPS-challenged), or pair-fed to receive the same amount of feed as the LPS-challenged pigs (pair-fed). The absence of interactions (P > .10) between diet complexity and immune challenge with LPS indicated that the responses were independent. Control pigs were the heaviest (P < .01), LPS-challenged the lightest (P < .01), and pair-fed intermediate in weight on d 18 after weaning. Approximately two thirds of the decreased growth of LPS-challenged pigs was due to decreased ADFI and one third was due to decreased feed efficiency (G/F). Pigs fed the complex diet were heaviest (P < .05), and pigs fed the simple diet were lightest (P < .05) on d 18 after weaning. The increased growth of pigs fed the complex compared with those fed the medium diet was due to the increased ADFI of the former. The decreased growth of pigs fed the simple diet compared with those fed the medium or complex diets was due to both decreased ADFI and G/F. The LPS-challenged pigs had increased (P < .01) haptoglobin concentrations, suggesting that inflammatory cytokine production was higher in immune-challenged pigs. These data suggest that LPS immune challenge caused decreased growth by decreasing ADFI and altering nutrient partitioning and that growth responses to diet complexity are independent of immune challenge.     

Evaluation of potato proteins on the growth performance of early-weaned pigs

We conducted five experiments to evaluate conventional and low-glycoalkaloid potato protein (CPP and LGPP, respectively) in diets for early-weaned pigs. In Exp. 1, 150 weanling pigs (initially 4.4 +/- .9 kg and 15.5 +/- 2 d of age) were fed either a control diet containing 3% spray-dried animal plasma (SDAP) or diets with additional SDAP (2.5 or 5% added; 5.5 or 8% total) or CPP (2.6% or 5.1%) substituted on a total lysine basis. From d 0 to 14 after weaning, increasing SDAP increased (linear, P < .05) ADG and ADFI, whereas increasing CCP had no effect on growth performance. In Exp. 2, 180 weanling pigs (initially 5.9 +/- 1.2 kg and 20 +/- 2 d of age) were fed diets containing a LGPP replacing 25, 50, 75, or 100% of the 7% dietary SDAP on a digestible lysine basis. From d 0 to 7 after weaning, increasing LGPP increased and then returned to control levels ADG and ADFI (quadratic, P < .01) and gain:feed ratio (quadratic, P < .05). In Exp. 3, 175 weanling pigs (initially 5.5 +/- 1.1 kg and 20 +/- 3 d of age) were fed either a control diet containing 20% dried whey, 17.5% dried skim milk, and 4% select menhaden fish meal (SMFM) or diets consisting of lactose and either 3.5 and 7.0% SDAP or 4.0 and 8.0% LGPP added at the expense of dried skim milk on a digestible lysine basis. From d 0 to 7 after weaning, ADG and ADFI increased (linear, P < .05) with increasing SDAP. With increasing LGPP, ADG and ADFI increased and then decreased (quadratic, P < .10 and P < .05, respectively). Gain:feed ratio (G/F) was not affected by SDAP and was improved (linear, P < .05) for pigs fed increasing LGPP. In Exp. 4, 270 weanling pigs (initially 6.2 +/- 1.6 kg and 20 +/- 3 d of age) were used to compare three diets that contained either 2.5% spray-dried blood meal (SDBM), 4.8% SMFM, or 3.92% CPP; test feedstuffs were substituted on a total lysine basis and diets were fed from d 7 to 28 after weaning. Pigs fed CPP had decreased (P < .05) ADG and G/F compared with those fed the other protein sources. In Exp. 5, 255 weanling pigs (initially 5.3 +/- 1.2 kg and 17 +/- 2 d of age), were used to compare five diets that contained either 2.5% SDBM, 5.51% SMFM, 4.17% CPP, 4.17% LGPP or 8.34% LGPP; feedstuffs were substituted on a digestible lysine basis and diets were fed from d 7 to 28 after weaning. No differences (P > .10) were observed in growth performance among pigs fed any of the protein sources within the experiment. However, pigs fed the LGPP had numerically greater ADG and better G/F than those fed CPP. In conclusion, these results suggest that LGPP can be an effective replacement for a portion of the SDAP in diets for weanling pigs.     

Relationships among ewe milk production and ewe and lamb forage intake in Suffolk and Targhee ewes nursing single or twin lambs

Suffolk and Targhee ewes (30 each) with single or twin lambs were used in four periods beginning in late gestation and continuing through weaning to evaluate breed differences in milk production, lamb BW, and DMI by ewes and lambs. In Periods 1 (late gestation) and 2 (early lactation), ewes (Period 1) and ewes with lambs (Period 2) were individually penned, fed .45 kg of barley x ewe(-1) x d(-1) and allowed ad libitum access to chopped alfalfa. Ewes and lambs grazed native range in Periods 3 and 4. Grazed forage DMI was estimated using chromic oxide. Estimates of milk production were obtained by handmilking. Average lamb age was 4, 45, and 73 d at the beginning of Periods 2, 3, and 4, respectively. Milk production tended (P = .20) to be greater for Suffolk than for Targhee ewes. Targhee ewes produced 85% more (P = .001) wool than Suffolk ewes. From 33 d prepartum to 89 d postpartum, Suffolk ewes consistently weighed more (P = .001) than Targhee ewes. Suffolk ewe BW loss (-.15 kg/d) was greater (P = .01) than Targhee ewe BW loss (-.02 kg/d) from 33 d prepartum to 6 d postpartum. From 6 to 89 d postpartum BW gain did not differ (P = .69; .05 kg/d) between breeds. From birth to 89 d postpartum, Suffolk lambs consistently weighed more than Targhee lambs (P = .003). From birth to 89 d postpartum, ADG was greater for Suffolk than for Targhee lambs (P = .006). Targhee ewes consumed 25% more (P = .01) feed over the course of the study than did Suffolk ewes. Grazed forage DMI by Targhee lambs was 26% greater (P = .01) than DMI by Suffolk lambs. When meat production is the primary income from sheep, one potential advantage of Suffolks compared with Targhees is more rapid gain with less feed intake.     

A method for selecting data subsets from large medical data bases

Response of tissues to homeostatic signals may play a role in the mediation of nutrient partitioning effects of somatotropin. To investigate this, the effects of exogenous porcine somatotropin (pST) on the metabolic responses to a series of intravenous challenges with dextrose, insulin and epinephrine were examined in twelve crossbred barrows (65 kg). In addition, the hyperinsulinemic-euglycemic clamp technique was used to further explore effects of pST on insulin resistance in eight of these animals. Pigs received daily sc injections of either pituitary-derived pST (120 micrograms/kg bw) or an equivalent volume of excipient for 28 d. Treatment with pST resulted in a chronic elevation of plasma glucose, insulin and non-esterified fatty acid concentrations and lowered glucagon concentrations. Acute iv challenges of dextrose (100 mg/kg bw), insulin (1.0 micrograms/kg bw), and epinephrine (2.2 micrograms/kg bw) were administered on days 21, 22, and 23 of the treatment period, respectively. Hyperinsulinemic-euglycemic clamps were carried out on day 28. Effects of pST were most dramatic for responses associated with insulin. In pST-treated pigs, insulin response to dextrose infusion was enhanced, while glucose response to insulin was attenuated and glucose clearance rate was reduced. During the hyperinsulinemic-euglycemic clamp, dextrose infusion rate required to maintain euglycemia during physiologic elevations of insulin was reduced in pST-treated pigs to 28% of control. In pST-treated pigs, glucose response to epinephrine challenge was halved, while insulin response was increased three-fold. Therefore, one mechanism by which pST shifts the nutrient partition is by altering metabolic responses to homeostatic signals. In growing pigs, this is especially evident for glucose response to insulin.     

Porcine follicle-stimulating hormone treatment of gilts during an altrenogest-synchronized follicular phase: effects on follicle growth, hormone secretion, ovulation, and fertilization

Porcine FSH (SUPER OV), containing .03% LH activity, and equine chorionic gonadotropin (eCG) were administered during an altrenogest-synchronized follicular phase to determine their effects on follicle development, estrus, ovulation, and fertilization. Treatments were made by i.m. injection starting on d 1 (24 h after the last feeding of altrenogest): 1) saline, once, n = 14; 2) eCG (1,200 to 1,500 IU) once, n = 32; 3) FSH 14 (n = 2) or 21 (n = 6) NIH-FSH-S1 units/100 kg BW, divided among six injections at 12-h intervals (FSH14/21); 4) FSH, 28 NIH-FSH-S1 units/100 kg BW, divided among six injections at 12-h intervals, n = 12; and 5) FSH, 28 NIH-FSH-S1 units/100 kg BW and 100 IU hCG, two or six injections at 12-h intervals (FSH28+hCG), n = 13. Gilts were injected with 750 IU of hCG on d 5 to ensure ovulation. Twenty-eight eCG- and FSH-injected gilts (n = 6, 8, and 11 on treatments 3, 4, and 5, respectively) were bred and laparotomized on d 7 to recover ova and record ovulation rate. The mean number of ovulations and large (6- to 10-mm) follicles, respectively, on d 7 were as follows: saline (17, .7), eCG (43, .9), FSH14/21 (15, .6), FSH28 (12, 16), and FSH28+hCG (32, 21). Plasma FSH concentrations were at least threefold higher (P < .05) in gilts treated with FSH than in gilts not treated with FSH. The percentage in estrus was higher (P < .05) for saline- and eCG-treated gilts (100 and 87%, respectively) than for FSH-treated gilts (53%). Proportion of FSH28+hCG-treated gilts with fertilized ova (27%) was lower than for other groups (79 to 100%). In summary, the 3-d high dose FSH treatment (FSH28 and FSH28+hCG) during an altrenogest-synchronized follicular phase increased the number of potentially ovulatory follicles, but this potential benefit was not realized because many follicles failed to ovulate. The co-injection of low doses of hCG (FSH28+hCG) increased the ovulation rate and estradiol secretion but reduced ova recovery and fertilization rate compared with eCG and the other FSH treatments.     

Effects of 6-N-propyl-2-thiouracil on growth, hormonal profiles, carcass and reproductive traits of boars

Neonatal 6-N-propyl-2-thiouracil (PTU)-induced hypothyroidism reduces body weight but increases testicular size in adult male rodents. The objective of this study was to determine the effect of prepubertal PTU treatment on boars. For Experiment I, boars (n = 28) were randomly allotted to eight pens. Each pen received one of four PTU doses (0, 0.01, 0.03 and 0.1% in a basal diet) between 28 and 56 days of age (DOA). Due to a lack of difference among three PTU treatments, PTU-treated boars were pooled. Boars treated with PTU had lower (P < 0.05) ADG during treatment, lighter (P < 0.05) BW after 56 DOA and less (P < 0.05) developed epididymides at 154 DOA. For Experiment II, boars (n = 19) were randomly allotted to six pens. Each pen received one of three PTU treatments orally as: control (carrier), PTU-I (0.002% BW of PTU daily between 7 and 70 DOA), or PTU-II (0.002% BW of PTU daily between 28 and 91 DOA). During treatment, PTU-treated boars had lower (P < 0.05) serum T4 levels, rectal temperature, feed intake and ADG. Boars treated with PTU had lower (P < 0.05) BW between 63 and 154 DOA but higher (P < 0.05) gain/feed between 105 and 133 DOA. Boars treated with PTU had less (P < 0.05) developed epididymides and sperm count per gram testis at 238 DOA. These results suggest that prepubertal PTU-induced hypothyroidism had significant effects on growth, hormonal profiles, and reproductive traits of boars; however, it does not appear to be an effective method for increasing testis size and sperm production of commercial boars.     

Influence of dietary magnesium level on growth-performance and metabolic responses of Holstein steers to laidlomycin propionate

We used 216 Holstein steers (151 kg) in a 262-d trial to evaluate the influence of dietary magnesium level (.19, .25, and .32%) and laidlomycin propionate (LP; 0 vs 11 ppm, air-dry basis) on growth performance and NE value of the diet. During the initial 112 d of the trial, LP increased (P < .01) ADG (6.3%) and feed efficiency (4.2%). From d 112 until slaughter, LP increased (P < .05) ADG (9.7%) and feed efficiency (4.5%). Across the 262-d feeding period, LP supplementation enhanced (P < .01) ADG (8.9%) and feed efficiency (6.3%). There was an interaction (P < .05) between dietary Mg and LP on NE value of the diet. The enhancement in NE value of the diets owing to LP with .19, .25, and .32% dietary Mg were .5, 3.0, and 5.9%, respectively. Six Holstein steers (302 kg) were used in a 6 x 6 Latin square experiment to evaluate treatment effects on characteristics of ruminal and total tract digestion. There were no treatment interactions (P > .10) on site and extent of digestion of OM, starch, and N. Supplemental Mg increased (quadratic effect, P < .10) ruminal OM digestion. Neither LP nor dietary Mg level affected (P > .10) ruminal digestion of starch and feed N. Supplemental LP decreased (15%, P < .05) ruminal microbial efficiency. Total tract digestion of OM and N increased (linear effect, P < .01) with increasing dietary Mg level. There were interactions between LP and dietary Mg level on ruminal soluble-Mg concentration (linear effect, P < .01) and Mg absorption (quadratic effect, P < .05). Apparent total tract Mg digestion increased owing to LP (P < .01) and dietary Mg level (linear effect, P < .01). There were no treatment effects (P > .10) on ruminal pH. Dietary Mg level did not influence (P > .10) ruminal VFA concentrations or molar proportions. Supplemental LP increased (14%; P < .10) total ruminal VFA concentration but did not affect (P > .10) VFA molar proportions. We conclude that LP will increase daily weight gain and feed efficiency of calf-fed Holstein steers and that this response may be enhanced by increasing dietary Mg level.     

Serum concentrations of luteinizing hormone, growth hormone, and cortisol in gilts treated with N-methyl-D,L-aspartate during the estrous cycle or after ovariectomy

The objective of this experiment was to determine the effects of n-methyl-d,l-aspartate (NMA), an agonist of the neurotransmitter glutamate, on circulating concentrations of LH, GH, and cortisol in gilts treated during the luteal (n = 4) or follicular (n = 4) phase of the estrous cycle, or after ovariectomy (n = 4). Blood was sampled every 15 min for 10 h on each of two consecutive days. On the 1st d, two gilts from each group received i.v. injections of NMA (10 mg/kg BW) at h 4 and 6, and the remaining gilts received .9% saline (vehicle). The following day, gilts that had received NMA on the 1st d received vehicle, and gilts that had received vehicle on d 1 received NMA. All gilts received an i.v. challenge of GnRH (.1 microg/kg BW) at h 8 on each day. The NMA treatment increased (P < .01) LH pulse frequency in luteal-phase gilts by 125%. In contrast, NMA decreased (P < .05) mean concentrations of LH by 48% and suppressed (P < .01) LH pulse frequency by 33% in ovariectomized gilts. No characteristics of LH secretion were affected (P > .05) by NMA in follicular phase gilts. Serum LH concentrations for the 2-h period following GnRH were lower (P < .05) in follicular-phase gilts than in ovariectomized gilts and were 1.15 +/- .09 (mean +/- SE), .81 +/- .05, and .51 +/- .17 ng/mL for ovariectomized, luteal-phase, and follicular-phase gilts, respectively. Treatment with NMA increased circulating concentrations of GH by 334% (P < .01) and cortisol by 77% (P < .03) in all gilts. We suggest that the effects of NMA on LH release in gilts depend on the circulating steroidal milieu. In contrast, NMA evokes secretion of GH and cortisol irrespective of the reproductive status of treated gilts.     

L-ascorbyl-2-polyphosphate as a vitamin C source for segregated and conventionally weaned pigs

We conducted two experiments to evaluate the efficacy of a stable source of vitamin C for improving performance and iron status in early-weaned pigs. A preparation of L-ascorbyl-2-polyphosphate (Rovimix Stay-C 25, Roche Vitamins, Ames, IA and Bramus, NJ), which supplies 25% ascorbic acid activity in a stable form, served as the vitamin C source and was incorporated at dietary vitamin C levels of 0, 75, or 150 ppm. In Exp. 1, 72 pigs (14 +/- 2 d of age and 4.98 kg BW) were blocked based on initial BW and penned in groups of three (eight pens per treatment) in an off-site nursery for 42 d. Phase 1 lasted from d 0 to 14, Phase 2 from d 14 to 28, and Phase 3 from d 28 to 42 after weaning. Daily gain and gain:feed ratio (G/F) increased during Phase 1 (quadratic, P < .1 and P < .05, respectively), Phase 3 (linear, P < .1 and P < .01, respectively), and for the overall 42-d experiment (linear, P < .05 and P < .1, respectively) in response to increasing dietary vitamin C. At 14 d after weaning, plasma vitamin C increased (linear, P < .05) with increasing dietary vitamin C, but plasma iron, hemoglobin, and hematocrit were not influenced by dietary vitamin C. In Exp. 2, 120 pigs (20 +/- 3 d of age and 7.2 kg BW) were blocked based on initial BW and penned in groups of five (eight pens per treatment) in a conventional nursery system for 31 d. Phase 1 consisted of d 0 to 7, Phase 2 from d 7 to 17, and Phase 3 from d 17 to 31 after weaning. During the period from d 0 to 17 after weaning, ADG and G/F were improved (linear, P < .1) with increasing dietary vitamin C. At d 17 after weaning, plasma vitamin C and serum iron increased (linear, P < .05), but unbound iron-binding capacity and total iron-binding capacity decreased (linear, P < .05 and P < .1, respectively) with increasing dietary vitamin C. These results suggest that dietary vitamin C is needed during the first 42 d after weaning when pigs are weaned as early as 12 d of age and reared in an off-site nursery and during the first 17 d after weaning when pigs are weaned as early as 17 d of age and reared in a conventional nursery system. L-Ascorbyl-2-polyphosphate at a supplemental level of 75 ppm was adequate to meet the dietary vitamin C requirement of early-weaned pigs. Vitamin C supplementation with a stable product will improve performance in young pigs during the high-stress postweaning period and may be particularly beneficial to pigs weaned at a very early age.     

Malaria in humans: Plasmodium falciparum blood infection levels are linked to chromosome 5q31-q33

Blood serum concentration of IGF-I was analyzed to determine its relationship with individual postweaning feed efficiency (gain/feed) of 36 crossbred steer calves fed at three levels of feed intake (n = 12 at each level). Diets consisted of a corn silage-based growing diet for 84 d followed by a 91% concentrate finishing diet for 56 d. Dietary intake levels were at 80, 90, or 100% of ad libitum. Diets were formulated to ensure equal daily intake of protein, vitamins, and minerals across intake treatment levels. Intake was measured daily; ADG, DMI, and feed efficiency were calculated at 28-d intervals, through d 140. Individual weights and serum samples were collected at the beginning of the study and at 28-d intervals thereafter. The IGF-I concentrations were determined with a RIA. Data were analyzed as a multivariate split-plot in time. Imposed dietary intake restrictions did not affect serum IGF-I concentration (P = .90) or individual feed efficiency (P = .36), even though the least squares means for IGF-I concentration tended to decrease and the feed efficiency means tended to increase under the restricted intake levels. Serum IGF-I concentration, ADG, and feed efficiency were affected (P < .001) by collection date. Residual correlations between IGF-I concentrations at adjacent 28-d sampling times averaged .72. Diet intake level x sampling time interactions existed for ADG (P = .02) and feed efficiency (P < .001). Positive residual correlations of .28 (P < .001) and .16 (P = .07) existed between IGF-I and ADG and between IGF-I and feed efficiency, respectively. Regression analysis indicated that a 1 ng/mL increase in serum IGF-I concentration was associated with a .00135 kg/d increase in ADG (P < .001) and a .0001 kg gain/kg feed increase in feed efficiency (P = .04). These results support the hypothesis that serum IGF-I plays a role in growth and in efficiency of feed utilization in beef cattle.     

The effect of dietary oil containing (n-3) fatty acids on the fatty acid, physicochemical, and organoleptic characteristics of pig meat and fat

An investigation was made to alter the fatty acid composition of pork and a pork product in line with human dietary advice while not adversely affecting factors controlling consumer acceptability. Pigs (n = 150) were assigned to three dietary treatments with 25 intact male-female pairs per treatment. Diet A (control) contained 3% of a 4:1 (wt/ wt) tallow-soybean oil mixture. Diets B and C contained 2% rapeseed oil plus 1% fish oil. Diets A, B, and C were supplemented with 100, 100, and 250 mg of all-rac-alpha-tocopheryl acetate/kg of diet, respectively. Pigs were given ad libitum access to feed from 52 kg live weight until 95 kg (slaughter). Sausages were prepared from the resulting cuts. Tissues of pigs were evaluated in terms of fat firmness, color, fatty acid composition, and contents of alpha-tocopherol and thiobarbituric acid-reactive substances (TBARS). Organoleptic characteristics of chops and sausages were evaluated by a trained taste panel. Pigs fed Diets B and C had improved feed conversion ratios (P < .05) and ADG compared with control pigs. The levels of n-3 (omega-3) polyunsaturates were significantly increased in the tissues and sausage from pigs fed Diets B and C with associated alterations in n-6 to n-3 fatty acid ratios that accorded with contemporary human dietary recommendations. Levels of alpha-tocopherol and TBARS were significantly altered in the tissues. There were no appreciable differences between treatments in carcass characteristics, including color. The overall organoleptic acceptability of chops and sausages was not different between the treatments.     

Cottonseed meal or feather meal supplementation of ammoniated tropical grass hay for yearling cattle

Despite high N intake by cattle consuming ammoniated forages, improvements in ADG might be expected be feeding proteins that supply ruminally available and(or) undegraded intake protein. Growth studies with 220-kg steers were conducted to evaluate ammoniated hay plus a liquid cane molasses-based supplement containing urea or a combination of urea and .07, .14, or .21 kg of CP daily from cottonseed meal (CSM) or feather meal (FM). Steers grazed dormant pasture and were fed hay plus 1.36 kg of DM daily per steer of the supplement. In each of 3 yr, total DM intake was similar (P > .60) among treatments, averaging 3.0% of BW. Daily gain by steers supplemented with urea and maximum ADG were similar across years, ranging from .21 to .23 kg and .50 to .60 kg, respectively. In all years for CSM supplementation, and in two of the three years for FM supplementation, increasing level of CP supplementation resulted in linear (P < .01) increases in ADG and gain:feed ratio (GF), with no differences (P > .10) between the protein sources. In one year, ADG and GF by steers supplemented with FM were maximized at the .07 kg of CP level, suggesting greater efficiency of protein utilization in FM. Improved performance by cattle fed ammoniated tropical grass hay may be obtained by feeding a protein supplement that provides preformed protein that is either moderately or highly resistant to ruminal degradation. Ruminal degradation characteristics of protein sources may influence efficiency of protein utilization in cattle fed ammoniated tropical grass hay plus molasses-based supplements.     

Effect of level of chronic immune system activation on the growth and dietary lysine needs of pigs fed from 6 to 112 kg

The effect of a low and a high level of chronic immune system (IS) activation on the rate, efficiency, and composition of body growth and dietary lysine needs of pigs fed from 6 to 112 kg body weight was evaluated. All pigs were of a single genetic strain and geographical site of origin, and the low and high IS pigs were created by physically isolating pigs from and continually exposing pigs to major vectors of environmental antigen transmission. In each IS group, five littermate barrows from each of seven litters were individually penned and randomly allotted to one of five dietary amino acid regimens (.6, .9, 1.20, 1.50, and 1.80% lysine from 6 to 27 kg BW and .45, .60, .75, .90, and 1.05% lysine from 27 to 112 kg BW). Dietary lysine concentrations were achieved by altering the ratio of corn to soybean meal in the diets, and diets were formulated such that lysine was the first-limiting amino acid. Low IS pigs possessed lower (P < .01) T lymphocyte CD4+:CD8+ ratios and serum alpha-1-acylglycoprotein concentrations. Low IS pigs also consumed more (P < .01) feed, gained body weight faster (P < .01), required less (P < .01) feed per unit of gain, and at 112 kg BW produced bodies with more (P < .12) muscle and less (P < .10) fatty tissue and offal than high IS pigs. To allow their elevated capacities for proteinaceous tissue to be expressed, low IS pigs required .15 to .30 percentage units greater dietary lysine concentrations and 2 to 5 g higher daily lysine intakes at each 14-kg BW increment from 6 to 112 kg BW.