Long-term recombinant porcine somatotropin (PST) treatment mitigates the responses to subchronic lipopolysaccharide in swine.

The effect of multiple lipopolysaccharide (LPS) challenges in swine undergoing long-term treatment with porcine somatotropin (PST) was determined. Changes in aspartate serine transaminase (AST) occurred only at 24h following the first LPS challenge dose (P<0.05), while PST treatment moderated any change from occurring. Nonesterified free fatty acid (NEFA) levels were elevated in PST treated animals for the first 3 days following daily LPS treatment (P<0.05), while LPS treatment alone had no effect on plasma NEFA levels. Plasma urea nitrogen (PUN) levels were unchanged by LPS following the initial LPS challenge, but were decreased following the second challenge dose (P=0.014). These changes were long lasting, with a return to normal PUN levels not evident until Day 6. The PST treatment mitigated changes in PUN (P<0.05) when LPS was administered. Haptoglobin plasma levels, along with lipid peroxide production were not affected by LPS challenge or PST administration. LPS challenge reduced the levels of immunoreactive heat shock protein 70 (HSP70) throughout the entire challenge period (P<0.001). PST-LPS animals had normal levels of this protein. The results of the present study demonstrate that long-term PST treatment mitigates the adverse effects of subchronic LPS administration.

Effect of dietary betaine on nutrient utilization and partitioning in the young growing feed-restricted pig.

The purpose of this study was to examine the effects of dietary betaine over a range of concentrations (between 0 and 0.5%) on growth and body composition in young feed-restricted pigs. Betaine is associated with decreased lipid deposition and altered protein utilization in finishing pigs, and it has been suggested that the positive effects of betaine on growth and carcass composition may be greater in energy-restricted pigs. Thirty-two barrows (36 kg, n = 8 pigs per group) were restrictively fed one of four corn-soybean meal-skim milk based diets (18.6% crude protein, 3.23 Mcal ME/kg) and supplemented with 0, 0.125, 0.25, or 0.5% betaine. Feed allotment was adjusted weekly according to BW, such that average feed intake was approximately 1.7 kg for all groups. At 64 kg, pigs were slaughtered and visceral tissue was removed and weighed. Carcasses were chilled for 24 h to obtain carcass measurements. Subsequently, one-half of each carcass and whole visceral tissue were ground for chemical analysis. Linear regression analysis indicated that, as betaine content of the diet was elevated from 0 to 0.5%, carcass fat concentration (P = 0.06), P3 fat depth (P = 0.14) and viscera weight (P = 0.129) were decreased, whereas total carcass protein (P = 0.124), protein deposition rate (P = 0.98), and lean gain efficiency (P = 0.115) were increased. The greatest differences over control pigs were observed in pigs consuming 0.5% betaine, where carcass fat concentration and P3 fat depth were decreased by 10 and 26%, respectively. Other fat depth measurements were not different (P > 0.15) from those of control pigs. In addition, pigs consuming the highest betaine level had a 19% increase in the carcass protein:fat ratio, 23% higher carcass protein deposition rate, and a 24% increase in lean gain efficiency compared with controls. Dietary betaine had no effects (P > 0.15) on growth performance, visceral tissue chemical composition, carcass fat deposition rate, visceral fat and protein deposition rates, or serum urea and ammonia concentrations. These data suggest that betaine alters nutrient partitioning such that carcass protein deposition is enhanced at the expense of carcass fat and in part, visceral tissue.

Methyl-beta-cyclodextrin: an alternative carrier for intravenous infusion of palmitate during tracer studies in swine (Sus scrofa domestica).

Fatty acid-free albumin has been the standard carrier for intravenous infusion of fatty acids to study in vivo lipid metabolism. However, subjects can have adverse reactions to infusion of albumin. We sought an alternative to albumin as a carrier for intravenous infusion of fatty acids, using the pig as a model. Cyclodextrins are naturally occurring water-soluble molecules that can serve as carriers for lipid-soluble compounds. 13C-palmitate was complexed to either 20% methyl-beta-cyclodextrin, 20% 2-hydroxypropyl-beta-cyclodextrin, or 5% porcine albumin (isotopic purity of infusates: 99.22+/-0.06%). 13C-palmitate-albumin was infused under fed conditions and 13C-palmitate-methyl-beta-cyclodextrin was infused under fasted and fed conditions in 50-kg pigs. Palmitate remained in solution at 4 degrees C in methyl-beta-cyclodextrin, but precipitated at 25-30 degrees C in 2-hydroxypropyl-beta-cyclodextrin. Pigs infused with 13C-palmitate-methyl-beta-cyclodextrin maintained normal body temperature and appetite; those infused with 13C-palmitate-albumin became anorexic and exhibited other negative side effects to albumin. Palmitate oxidation rates under fed conditions were similar using either 13C-palmitate-methyl-beta-cyclodextrin or 13C-palmitate-albumin complexes. Fasting increased 13C-palmitate-methyl-beta-cyclodextrin oxidation by approximately eight-fold. These data suggest that methyl-beta-cyclodextrin may be a suitable substitute for albumin in fatty acid metabolism studies in swine.

Dietary conjugated linoleic acid alters fatty acid composition of pig skeletal muscle and fat.

The dietary dose responsiveness of conjugated linoleic acid (CLA) addition relative to the fatty acid profile of edible lean tissue was examined in grower pigs treated with or without porcine somatotropin (pST). Gilts and barrows were fed CLA at 0, 0.25, 0.5, 1.0, or 2.0% of diet by weight from 20 to 55 kg BW. Additional pigs were administered (pST) at 0 or 100 microg x kg BW x d(-1) and fed either 0.5 or 2.0% CLA. Animals were fed diets containing 18% CP, 1.2% lysine, and 3.5 Mcal of DE/kg at 110% of ad libitum intake. The fatty acid profile in latissimus dorsi and dorsal s.c. adipose tissue samples was determined by gas chromatography. Dietary CLA replacement of corn oil increased the percentage of total fatty acids as stearic acid, whereas the percentages as oleic and linolenic acids were reduced in lattisimus muscle. Treatment with CLA + pST increased the percentages of linoleic and arachidonic acids while reducing the percentages of palmitic and oleic acids in lattisimus muscle. Dietary CLA increased the percentages of palmitic and stearic acids in s.c. adipose tissue while reducing the percentages of oleic, linoleic, linolenic, and arachidonic acids. The percentage of palmitic acid was reduced in s.c. adipose tissue, whereas linoleic acid was increased with CLA + pST. No synergistic effect was detected between CLA and pST for reducing carcass lipid content in grower pigs. However, pST increased the percentage of polyunsaturated fatty acids in lattisimus muscle and s.c. adipose tissue while reducing the percentages of saturated fatty acids in swine fed CLA.

Somatotropin increases protein balance independent of insulin's effects on protein metabolism in growing pigs.

Somatotropin (ST) administration enhances protein deposition and elicits profound metabolic responses, including hyperinsulinemia. To determine whether the anabolic effect of ST is due to hyperinsulinemia, pair-fed weight-matched growing swine were treated with porcine ST (150 microg x kg body wt(-1) x day(-1)) or diluent for 7 days (n = 6/group, approximately 20 kg). Then pancreatic glucose-amino acid clamps were performed after an overnight fast. The objective was to reproduce the insulin levels of 1) fasted control and ST pigs (basal insulin, 5 microU/ml), 2) fed control pigs (low insulin, 20 microU/ml), and 3) fed ST pigs (high insulin, 50 microU/ml). Amino acid and glucose disposal rates were determined from the infusion rates necessary to maintain preclamp blood levels of these substrates. Whole body nonoxidative leucine disposal (NOLD), leucine appearance (R(a)), and leucine oxidation were determined with primed, continuous infusions of [(13)C]leucine and [(14)C]bicarbonate. ST treatment was associated with higher NOLD and protein balance and lower leucine oxidation and amino acid and glucose disposals. Insulin lowered R(a) and increased leucine oxidation, protein balance, and amino acid and glucose disposals. These effects of insulin were suppressed by ST treatment; however, the protein balance remained higher in ST pigs. The results show that ST treatment inhibits insulin's effects on protein metabolism and indicate that the stimulation of protein deposition by ST treatment is not mediated by insulin. Comparison of the protein metabolic responses to ST treatment during the basal fasting period with those in the fully fed state from a previous study suggests that the mechanism by which ST treatment enhances protein deposition is influenced by feeding status.

Somatotropin increases protein balance by lowering body protein degradation in fed, growing pigs.

Somatotropin (ST) administration enhances protein deposition in well-nourished, growing animals. To determine whether the anabolic effect is due to an increase in protein synthesis or a decrease in proteolysis, pair-fed, weight-matched ( approximately 20 kg) growing swine were treated with porcine ST (150 microg. kg(-1). day(-1), n = 6) or diluent (n = 6) for 7 days. Whole body leucine appearance (R(a)), nonoxidative leucine disposal (NOLD), urea production, and leucine oxidation, as well as tissue protein synthesis (K(s)), were determined in the fed steady state using primed continuous infusions of [(13)C]leucine, [(13)C]bicarbonate, and [(15)N(2)]urea. ST treatment increased the efficiency with which the diet was used for growth. ST treatment also increased plasma insulin-like growth factor I (+100%) and insulin (+125%) concentrations and decreased plasma urea nitrogen concentrations (-53%). ST-treated pigs had lower leucine R(a) (-33%), leucine oxidation (-63%), and urea production (-70%). However, ST treatment altered neither NOLD nor K(s) in the longissimus dorsi, semitendinosus, or gastrocnemius muscles, liver, or jejunum. The results suggest that in the fed state, ST treatment of growing swine increases protein deposition primarily through a suppression of protein degradation and amino acid catabolism rather than a stimulation of protein synthesis.

Ontogenic maturation of the somatotropin/insulin-like growth factor axis.

The ontogeny of the somatotropin/insulin-like growth factor system was examined in well-fed pigs under basal conditions and during a short-term challenge of porcine ST (pST). The study was conducted with two replicates of eight castrate male pigs from 3.8 kg BW (10 d of age) to 92 kg BW (129 d of age). Pigs were reared individually with ad libitum access to milk replacer through 23 d of age. Thereafter, pigs were fed a corn, soybean meal, and dry skim milk diet formulated to exceed nutrient requirements by approximately 30%. Pigs were randomly assigned to receive daily i.m. injections of either 0 (buffer) or 120 microg/kg BW of pST for a duration of 4 d starting at 10, 19, 33, 43, 63, 83, and 125 d of age. Blood was collected via jugular venipuncture on d 0 and 4 of the challenge. Circulating levels of IGF-I were not dramatically affected by age, but levels of IGF-II were low from 10 to 19 d of age and then increased through later stages of growth. Circulating concentrations of IGF binding protein (BP)-3 increased with age (P < .05), but levels of IGFBP-2, a 30-kDa IGFBP, and IGFBP-4 were unchanged (P > .10). The pST challenge reduced plasma urea nitrogen at all ages, but the magnitude of the response was less in younger pigs compared with the maximum response in pigs greater than 30 kg BW (63 d of age). The IGF-I response to the pST challenge also increased from approximately 30% in young pigs to a threefold increase in older pigs. Regardless of age, concentrations of IGF-II were minimally affected by the pST challenge. Circulating levels of IGFBP-3 increased and IGFBP-2 levels decreased in response to the pST challenge, and the magnitude increased with age. The high nutritional status of pigs in the early phases of growth diminished the postnatal changes in IGF-I and IGFBP-2, but not IGF-II or IGFBP-3. Overall, data demonstrate a developmental regulation of the ST/IGF system, with pST challenges altering circulating concentrations of IGF-I, IGFBP-3, and IGFBP-2 coincident with changes in amino acid metabolism.

Challenge differentially affects cytokine production and metabolic status of growing and finishing swine.

Growing (35 kg body weight) and finishing (85 kg body weight) swine challenged with endotoxin (Escherichia coli O55:B5) at a dose of either 2 or 20 microg/kg produced tumor necrosis factor (TNF)alpha in a dose-response relationship as measured by bioassay. Peak TNFalpha plasma levels were observed 1-2 hr post-challenge, returning to basal values 4 hr post-challenge. However, both an enzyme-linked immunosorbent assay specific for swine TNFalpha and total human TNFalpha demonstrated no dose-response relationship; peak plasma levels of immunoreactive TNFalpha were also observed 1-2 hr post-challenge. Maximal plasma interleukin-6 levels occurred 1-2 hr post-challenge and remained elevated through 8 hr post-challenge; there was no effect of lipopolysaccharide dose or metabolic status. Although the metabolic status of the animals also affected glucose levels, with growing animals exhibiting greater sensitivity compared with finishing animals, endotoxin-induced decreases in blood glucose levels were primarily dose-dependent. In contrast, changes in plasma urea nitrogen and free fatty acid (FFA) levels were strictly related to the metabolic status. Urea nitrogen levels were unchanged in growing swine, whereas they were increased in finishing swine and remained elevated 24 hr post-challenge. FFA levels in growing and finishing swine increased 3-6 hr post-challenge. FFA levels returned to basal values for finishing swine 24 hr post challenge, but in growing swine remained elevated 24 hr post-challenge. Plasma aspartate transaminase levels were increased through 24 hr post-challenge; animals given a dose of 20 microg/kg exhibited the greatest increase. Similarly, swine challenged with a dose of 20 microg/kg also exhibited the greatest increase in levels of conjugated bilirubin; there was no effect on unconjugated (free) bilirubin. These results demonstrate that endotoxin challenge of swine result in a pattern of changes that are dependent on both the dose of endotoxin used and the metabolic status of the animal examined.

Redefining body composition: nutrients hormones, and genes in meat production.

Growth rate and body composition of livestock can be optimized to meet consumer needs for a leaner product and to improve the efficiency of meat-animal production. Optimization strategies have traditionally focused on genetic selection and cost-effective ration formulation to achieve the genetic potential. Advances in understanding the mechanisms of growth and its control have led to additional opportunities for its manipulation. These include nutritional manipulation,the use of growth promotants, and, more recently, the ability to change the genetic potential through genetic engineering. Selection of appropriate candidate genes for manipulation depends on understanding the mechanisms underlying differentiation and growth of embryonic muscle cells. Recent advances in genetic engineering techniques, including gene therapy and germline transgenesis, will likely hasten the genetic progress toward a leaner carcass in domestic livestock. Such strategies may prove to be more beneficial then the controlled enhancement of somatotropin expression.

Porcine somatotropin, dietary protein and energy effects on arginase and transaminase activities in pigs.

Two experiments were conducted with cross-bred barrows to determine the effect of somatotropin administration on liver enzyme activities. In the first experiment, pigs growing from 26 to 55 kg body weight were given two doses of pituitary porcine somatotropin (pST; 0 and 100 micrograms per kg body weight) and three levels of dietary energy (60, 80 and 100% of free choice intake). In the second experiment, pigs growing from 30 to 60 kg body weight were given two doses of recombinant porcine somatotropin (rpST; 0 and 100 micrograms per kg body weight) and five levels of dietary crude protein (110, 150, 190, 230 and 270 g crude protein/kg diet). Liver arginase (ARG, EC 3.5.3.1) and aspartate aminotransferase (AAT, EC 2.6.1.1) activities were then determined in organ samples taken at slaughter time. Dietary energy did not change liver ARG. Activities of both ARG and AAT increased as dietary crude protein increased. Both pST and rpST decreased ARG, AAT and serum utrea nitrogen. There was a lack of interaction between rpST therapy and dietary protein on either ARG or AAT activities, suggesting that set nutritional states are not required for expression of pST effects.

Effects of an endotoxin challenge on growth performance, carcass accretion rates, and serum hormone and metabolite concentrations in control pigs and those treated with recombinant porcine somatotropin.

Barrows were restrictively fed starting at 20 kg BW to determine the effects of endotoxin on growth performance of control and somatotropin-treated pigs. The following treatments were used: 1) daily i.m. vehicle injection until 55 kg BW; 2) daily i.m. injections of 100 micrograms of recombinant porcine somatotropin (pST)/kg BW, until 55 kg; 3) i.v. saline injections for 7 d consecutively starting at 60 kg BW; 4) i.v. injections of 1 microgram of bacterial lipopolysaccharide (LPS)/kg BW for 7 d starting at 60 kg BW; and 5) the combined LPS+pST treatment, with pST injections from 20 kg through the 7 d of LPS treatment. Pigs evaluated for LPS effects were fed to 60 kg anticipating a weight loss. Pigs were bled at 0800 and 1100 at 55 kg and on d 7 of LPS treatment. Rectal temperatures were taken on d 7. Treatment with pST increased ADG by 13 to 20% and improved feed:gain by 17 to 23% before LPS treatment. During the 7 d of LPS injections, ADG and feed:gain did not differ, although feed efficiency was impaired and variable. Rectal temperatures at 1100 were progressively increased: control < LPS < LPS-pST (P < .01). Protein accretion was improved 27% by pST treatment, and lipid accretion was decreased 45% before LPS. Lipid stores decreased (P < .01) after LPS treatment in the pST-treated pigs. Lipopolysaccharide treatment and(or) decreased feed intake reduced the hyperinsulinemia and hyperglycemia (P < .01) associated with pST treatment. These results indicate that LPS induced a simulated septicemia and that the effects were not negated by pST treatment. The observed hyperthermia was additive, possibly due to increased lean body mass induced by pST combined with the pyrogenic effect of LPS.

Effect of growth hormone or chromium picolinate on swine metabolism and inflammatory cytokine production after endotoxin challenge exposure.

OBJECTIVE: To determine whether recombinant porcine somatotropin (PST) or chromium picolinate (CrP) affected cytokine production and metabolism in swine after endotoxin challenge exposure. ANIMALS: 20 Poland China X Landrace pigs, 5/group. PROCEDURE: Pigs were given CrP-supplemented feed at body weight of 20 kg; PST treatment began at 60 kg, and both treatments continued through body weight of 90 kg. At 90 kg, pigs were challenge exposed with 20 micrograms of lipopolysaccharide (LPS)/kg of body weight. Blood samples were obtained at various times through 24 hours after LPS challenge exposure. RESULTS: In all pigs not given PST, glucose concentration decreased 2 to 4 hours after LPS. In PST-treated pigs, blood glucose concentration was decreased at 6 to 8 hours after LPS. Plasma insulin concentration paralleled changes in glucose concentration. Nonesterified fatty acid concentration was high 2 to 24 hours after LPS in pigs not given PST and at 6 to 24 h in PST-treated pigs. Plasma urea nitrogen concentration was high at 6 to 24 hours after LPS in pigs not given PST. The urea nitrogen values in PST-treated pigs were lower at all times. Serum aspartate transaminase activity was high 6 to 24 hours after LPS in pigs not given PST, whereas PST treatment prevented the increase in this enzyme activity. In untreated (PST) pigs, plasma bilirubin (total and direct) concentrations were high 4 to 8 hours after LPS and returned to normal at 24 hours. The PST- and CrP-treated pigs maintained normal plasma bilirubin concentrations. Interleukin 6 activity was unaffected by CrP and PST treatments. Treatment with CrP and PST decreased the tumor necrosis factor alpha response to LPS, compared with that in control pigs. CONCLUSIONS: PST, and to a lesser extent CrP, provide protection against the adverse metabolic effects of LPS-induced septic shock.

Nutritional modulation of somatotropic axis-cytokine relationships in cattle: a brief review.

The objective of this review is to summarize data on the interrelationships that exist between nutrition, the endocrine system and their modulation of plasma tumor necrosis factor-alpha responses to endotoxin in cattle. During stress, intake of nutrients often is compromised and a percentage of available nutrients are diverted away from growth processes to stabilize other physiological processes of a higher survival priority. Management practices that minimize the magnitude and duration of disease stress will aid in speeding the return to homeostatic equilibrium. However, the shift away from growth during stress is almost inevitable as a mechanism to survive. Some degree of control and management of the metabolic cost of disease stress involves understanding the integration of nutritional, endocrine and immune signals by cells and working with the natural homeostatic processes. Endocrine hormones and immune system cytokine signals participate in redirecting nutrient use during disease stress. In an intricate interplay, hormones and cytokines regulate, modify and modulate each other's production and tissue interactions to alter metabolic priorities. Levels of dietary protein and energy intake affect patterns of hormones and cytokines in the blood after endotoxin challenge and further modulate the biological actions of many of these regulatory effectors. In vivo, administration of growth hormone to young calves has significant effects to decrease the many specific physiological responses to endotoxemia. Many aspects of nutrition can attenuate or facilitate this effect.

Beneficial effects of chromium on glucose and lipid variables in control and somatotropin-treated pigs are associated with increased tissue chromium and altered tissue copper, iron, and zinc.

Chromium (Cr) and somatotropin have been shown to increase lean body mass in pigs but by independent mechanisms. Somatotropin and Cr also affect blood glucose, lipids, and tissue trace metal concentrations. Twenty-four castrated male pigs were divided into four groups: 1) control basal diet; 2) basal diet + 300 micrograms of Cr/kg of diet as Cr picolinate; 3) basal diet + pituitary porcine somatotropin (ppST; 100 micrograms/kg live weight injected daily); and 4) basal diet + Cr + ppST. Pigs were fed the diets from 30 to 60 kg body weight and then killed. Supplemental Cr led to increased total Cr in kidney (1.1 vs 2.3 micrograms) and liver (5.9 vs 8.8 micrograms) but not in the heart independent of ppST treatment. Chromium concentrations in longissimus muscle were less than 1.5 ng/g in all samples, and any increases due to supplemental Cr were not detected. Somatotropin treatment led to decreased hepatic Cr, Cu, Fe, and Zn concentrations and increased total renal Cu, Fe, and Zn. These data demonstrate that supplemental Cr causes increased tissue Cr in the liver and kidney but not in the heart or muscle in control and somatotropin treated pigs. Somatotropin treatment caused decreased kidney and liver Cr concentrations that were offset by increased tissue weights. Somatotropin effects on tissue Cr, Cu, Zn, and Fe were variable and difficult to evaluate due in part to growth hormone-induced changes in organ weights.

Effect of porcine somatotropin administration in young pigs during the growth phase from 10 to 25 kilograms.

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

Tissue IGF-I protein and mRNA responses to a single injection of somatotropin.

Swine were divided into four groups of 11 animals at 40 kg body wt. Swine within a group were given a single porcine somatotropin (pST) injection (200 micrograms/kg) or buffer at 0800. Blood, liver (L), latissimus dorsi (LD), semitendinosus (STS), vastus lateralis (VL), dorsal subcutaneous (SQ), and perirenal (PR) adipose tissues were sampled at 0, 1, 2, 4, 8, 12, 16, and 24 h postinjection. Blood urea nitrogen was depressed by 16 h. Insulin was elevated by approximately 350% at 8 h. Lipogenic enzyme activities in adipose tissues were not affected by pST treatment. Insulin-like growth factor I (IGF-I) mRNA levels increased rapidly in SQ, PR, and L to a single pST administration, whereas they increased only slightly in VL. IGF-I mRNA concentrations in LD and STS were unaffected by pST treatment. IGF-I protein content of tissues changed little during the first 24 h postinjection. These data suggest that individual tissues differ in timing and degree of response to pST. Conflicting results reported after pST treatment could, in part, be due to tissue selection for sampling or sample timing.

Somatotropin enhances the rate of amino acid deposition but has minimal impact on amino acid balance in growing pigs.

This experiment was conducted to establish the influence of porcine somatotropin on tissue distribution and deposition rates of amino acids in growing pigs. Barrows were treated daily with buffer or porcine somatotropin (100 micrograms/kg body wt) when they weighed between 30 and 64 kg (eight pigs/group). Pigs were restrictively fed so that the average food intake was 1.86 kg/d. The corn-soybean meal-skim milk-based diet contained 18% crude protein and 1.2% lysine, and was designed to meet muscle amino acid ratio profile with respect to lysine as the first limiting amino acid for growth. Tissue levels of eighteen amino acids were determined on lyophilized samples that were appropriately hydrolyzed and analyzed by HPLC. The concentrations (mg/g dry wt) of all amino acids were greater in carcass, skin, head and empty body of porcine somatotropin-treated pigs; amino acid concentration in viscera was not influenced by porcine somatotropin. However, when the concentration of each amino acid was expressed on a per unit protein basis, the amino acid profiles of control and porcine somatotropin-treated pigs were quite similar. The average deposition rate of each amino acid was increased approximately 67% by porcine somatotropin. When the deposition of each amino acid was calculated in relation to lysine, however, the pattern of amino acid utilization for growth was similar for control and porcine somatotropin-treated pigs; exceptions were arginine, glycine and tryptophan. The ratio of indispensable to dispensable amino acids that were deposited was also similar for control and porcine somatotropin-treated pigs. These data indicate that the synthesis rate of individual proteins can be influenced by porcine somatotropin, but the balance of amino acids remains largely unaffected, suggesting that the changes in protein and amino acid metabolism elicited by porcine somatotropin are consistent with normal growth processes.

Effects of porcine somatotropin administration on porcine muscles located within different regions of the body.

This research was conducted to evaluate the characteristics of muscle fiber growth and the effects of porcine somatotropin (pST; 100 micrograms.kg-1 BW.d-1) administration on the morphology of 12 muscles located in different regions of the body in barrows growing from 20 to 90 kg BW. In the course of the growth of control pigs, the percentage distribution of beta R fibers did not show any changes in all 12 muscles, whereas the percentage of alpha R and alpha W fibers changed in different patterns in different muscles. The administration of pST had no effect on fiber type distribution. The cross-sectional area of alpha W fibers was the largest of the three fiber types, and beta R and alpha R fibers were of similar size in all muscles. All fiber types in all muscles increased in cross-sectional area by an average of 120% from 20 to 60 kg BW. After 60 kg BW, the growth of alpha W fibers in seven (early maturing) muscles and alpha R fibers in one muscle out of the 12 muscles was not apparent. The increase of their cross-sectional area was an average of 12%, but the area of the other muscle fibers continued to increase by an average of 38% until 90 kg BW. The administration of pST increased the area of alpha W fibers in four out of seven of these early-maturing muscles by an average of 25%, suggesting some possible relationships between pST effects and the rate of muscle fiber maturation. Most of the muscles that responded to pST treatment were located in hindlimb region.

Effect of dietary energy intake and exogenous porcine growth hormone administration on circulating porcine growth hormone concentration and response to human growth hormone-releasing factor administration in growing swine.

In a 2 x 2 treatment array (n = 4 pigs/treatment), the effects of feed intake (ad libitum vs. restricted to 60% ad libitum) and the daily administration of excipient buffer or porcine pituitary-derived growth hormone (GH) at a dose of 100 micrograms/kg body weight per day on serum GH profile and human growth hormone-releasing factor (hGRF) response were examined in barrows weighing 55 kg. Feed intake treatment was implemented from 25 to 55 kg live weight. Buffer or GH treatment was implemented for 10 d before sampling. After GH treatment, the integrated serum GH concentration area was 25% greater in barrows fed restrictively. Data are consistent with the suggestion that GH dose to improve the efficiency of lean tissue deposition be adjusted according to feeding regimen. The serum GH response to hGRF was also altered by level of feed intake. The ad libitum feeding of buffer-treated animals resulted in a monophasic serum GH response to hGRF, whereas barrows fed restrictively had a biphasic response to hGRF. Together, these data suggest that feed intake pattern alters GH secretion and as such could influence the practical implementation of somatotropin as a metabolism modifier in swine.

Effect of recombinant growth hormone and chromium picolinate on cytokine production and growth performance in swine.

The effect of dietary chromium picolinate (CrP) and recombinant porcine growth hormone, somatotropin (rPST) administration on growth performance and cytokine production in Landrace-Poland China gilts was determined using a 2 by 2 treatment array. Treatments were: (1) control (basal diet), (2) CrP-supplemented diet (basal diet + 300 micrograms Cr3+/kg diet as CrP), (3) rPST (100 pg/kg body weight/day), and (4) rPST+CrP. CrP-supplemented diets were fed beginning at 20 kg body weight through 90 kg. Administration of rPST was begun at 60 kg weight and continued through 90 kg. All rPST treated pigs demonstrated improvements in growth performance versus controls. Pigs given CrP-supplemented diets showed no differences in growth performance. At 90 kg, pigs were challenged with endotoxin (lipopolysaccharide, 0.2 microgram/kg i.v.). Blood samples were collected at 0, 1, and 3 h postchallenge. Plasma IL-6 levels increased from 23 U/ml at time 0 to 1,927 U/ml at 3 h for control swine. Swine from the CrP treatment group had IL-6 levels of 8,130 U/ml at 3 h post-LPS. There were no differences in plasma IL-6 from pigs in the rPST and rPST+CrP treatment groups compared to the controls. Endotoxin challenge had no effect on either blood glucose levels or induction of TNF-alpha in any treatment group. PBMC from CrP-treated animals produced more IL-2 than peripheral blood mononuclear cells from all other groups.