pST Administration Research Articles

Effects of porcine somatotropin administration on the responses to dietary lysine and a near-ideal blend of amino acids on the amino acid composition of whole-body protein and amino acid accretion rate in growing pigs.

An experiment was conducted to assess the effects of porcine somatotropin (pST) on the responses to a near-ideal blend of AA on the AA composition of empty, whole-empty body (WEB) protein and WEB essential AA accretion rate in pigs from 22 to 60kg BW. Forty Hampshire × Yorkshire gilts were individually penned and assigned to a 4 × 2 factorial arrangement of treatments consisting of four diets with and without pST injection. A fortified corn-soybean meal basal diet was formulated to contain 1.50% total Lys with Thr, Met, and Trp added to obtain a near-ideal blend of these AA relative to Lys. In three additional diets, Lys was reduced to 1.25%, 1.00%, and 0.75% by diluting the basal diet with cornstarch, cellulose, and sand such that the diets also contained the same ratios of AA. Pigs that received pST were administered a daily i.m. injection of 2mg of pST. At 60kg BW, the WEB (carcass, head, viscera, blood, nails, and hair) was ground and analyzed for proximate and AA composition. Administration of pST increased (P < 0.001) accretion rates of WEB protein and essential AA. Increasing dietary essential AA increased (quadratic, P < 0.03) accretion rate of WEB protein, His, Leu, Trp, and Val in pST-treated pigs, but not in untreated pigs. Lysine composition in the accreted WEB protein was not affected (P > 0.05) by dietary Lys. The efficiency of Lys utilization for WEB Lys accretion was linearly affected (P < 0.01) by dietary Lys. These results indicated that the dietary Lys needed to achieve maximum WEB Lys accretion is markedly increased by pST administration.

Effect of porcine somatotropin on metabolism and testicular characteristics of prepubertal pigs

The effect of pST on the testicular characteristics and metabolic parameters of prepubertal pigs was evaluated. Experiment 1 aimed to determine the interval between applications of pST based on the concentrations of circulating IGF-I. Experiment 2 aimed to evaluate the effect of pST on metabolic parameters, testicular characteristics, and expression of GHR, IGF-I and PCNA. In Experiment 1 twelve piglets with 30 days of age were used. The pST Group (n=6) was submitted to one i.m. injection of pST and the Control Group (n=6) to one placebo injection. Blood collections were performed until d 7 post pST application to determine IGF-I concentration and metabolic profile. In Experiment 2 twelve piglets with 22 days of age were used. The pST Group was submitted to pST injections every three days, and the Control Group received placebo doses during 30 days. Blood collections were performed every 3 days. Samples of liver and testicular tissue were collected to determine gene expression and testicular characteristics. In Experiment 1 IGF-I concentration was higher for the pST Group (P=0.02). In Experiment 2 the pST Group had higher body and testicular weight (P=0.06) and increased gene expression of PCNA in testes (P<0.05). However, a reduction in the number of seminiferous tubules, and Sertoli cells, and in GHR expression (P<0.05) was observed. Thus, pST administration increased body and testis development in prepubertal pigs, however it reduced the density of seminiferous tubules and Sertoli cells.

The effect of porcine somatotropin (pST) and gender on production parameters and tissue yield of pigs slaughtered at 135 kg live weight

Eighteen F1 crossbred (commercial-type terminal crosses) pigs (boars, barrows and gilts) with an initial weight of 27.2 ± 2 kg were used to investigate the effect of porcine somatotropin (pST) administered for six weeks prior to slaughter on production parameters and tissue yield in the South African scenario. Pigs were grown to 135 kg live weight, which is heavier than the average weight at slaughter in South Africa of 80 - 100 kg. Porcine somatotropin had no significant effect on average daily gain or feed intake. However, pST administration caused a significant increase in feed conversion ratio (kg feed/kg gain) of treated boars, indicating that boars converted their feed less efficiently when treated with pST. This contradicts most of the findings in the literature. The effect of pST on the different carcass cuts was not significant, except for the percentage loin back, which was higher for pST-treated animals and percentage middle back of boars and barrows, which was slightly higher. No significant pST effects were found for live weight, carcass weight, % bone, % fat or % lean meat, but a significant increase in percentage skin was found.

In vivo immunostimulatory and tumor-inhibitory activities of polysaccharides isolated from solid-state-cultured Trametes robiniophila Murrill

Crude polysaccharides extracted from successfully solid-state-cultured Trametes robiniophila (PST) showed cellular immunomodulatory and tumor-inhibitory activities in vivo. The different concentration of PST (100, 200, 400 mg kg−1 body weight) significantly enhanced immunity response in mice burden with Sarcoma 180 (S180) solid tumor. The results indicated that PST not only increased the macrophage phagocytosis and NO production, but also promoted lymphocyte proliferation and natural killer cell activity, and PST administration significantly inhibited tumor growth with the rate up to 60.9%. Interestingly, the most effective polysaccharides dosage on enhancing cellular immunity and inhibiting tumor was 200 mg kg−1 body weight each day. In conclusion, in vivo immunostimulatory and tumor-inhibitory activities of PST showed a non-dose-dependent manner, and suggested it could be used potentially in medicinal application.

Uncoupling protein expression in skeletal muscle and adipose tissue in response to in vivo porcine somatotropin treatment

These experiments examined the potential roles of somatropin (pST) and IGF-I in the regulation of uncoupling protein (UCP)2 and UCP3 and their regulatory proteins peroxisome proliferator activated receptor (PPAR) α, γ and δ using in vivo pST treatment of swine and in vitro supplementation of pST or IGF-I to adipose slices. Six, 90 kg barrows were treated with recombinant pST (10 mg) for 2 week while another six pigs were injected with buffer. Total RNA from outer subcutaneous adipose (OSQ) and middle subcutaneous adipose (MSQ) tissues, leaf fat, liver and longissimus (LM) was amplified by reverse transcription-PCR with quantification of transcripts by capillary electrophoresis with laser-induced fluorescence detection. UCP2 mRNA abundance increased in liver ( P < 0.001) and all three adipose tissues by pST treatment ( P < 0.05). Administration of pST increased UCP3 mRNA abundance by 42% in LM ( P < 0.01). PPARα mRNA abundance increased with pST treatment by 29% in liver ( P < 0.05), while decreasing 25% in LM ( P < 0.05). PPARγ mRNA abundance decreased 32% ( P < 0.01) while PPARδ increased 48% in LM ( P < 0.01) with pST administration. In vitro, pST reduced UCP2 mRNA abundance in OSQ and MSQ tissue slices ( P < 0.05). UCP3 mRNA abundance decreased in OSQ ( P < 0.05) but increased in MSQ ( P < 0.05) with pST. In contrast, IGF-I increased UCP2 and UCP3 mRNA abundance in both MSQ and OSQ slices ( P < 0.05). These experiments suggest pST, IGF-I and metabolic adaptations to pST contribute to regulating UCP2 and UCP3.

A GnRF vaccine (Improvac®) and porcine somatotropin (Reporcin®) have synergistic effects upon growth performance in both boars and gilts

The use of a vaccine (Improvac) directed against gonadotrophin-releasing factor (GnRF), to prevent boar taint in male pigs, is also associated with an increase in feed consumption, growth, and higher deposition of subcutaneous fat. Daily administration of porcine somatotropin (pST) consistently increases average daily gain, and feed conversion efficiency, and reduces subcutaneous fat, particularly in gilts. The objective of this study was to examine the effect of combining these treatments in boars and gilts. Forty-eight pigs (Large White × Landrace), housed individually, were used in a 2 × 2 × 2 factorial experiment with the respective factors being vaccination with GnRF vaccine (at 14 and 18 weeks of age), daily injection with pST (from 18 weeks to slaughter at 22 weeks), and sex (boars and gilts). Performance was measured over the period of pST administration. Over the entire 28 days of the study, daily gain was lower for gilts than for boars (1216 v. 1410 g/day, P &lt; 0.001), was increased by pST (1219 v. 1407 g/day, P &lt; 0.001), but not significantly altered by vaccination against GnRF (1284 v. 1342 g/day, P = 0.15). However, GnRF vaccination increased daily gain in the second 2 weeks of the study, and overall, there were interactions such that the vaccine increased gain in all groups except boars not receiving pST. Feed intake over the study period was less for gilts than for boars (3139 v. 3407 g/day, P &lt; 0.001), was decreased by pST (3537 v. 3009 g/day, P &lt; 0.001), and increased by vaccination against GnRF (3139 v. 3407 g/day, P &lt; 0.001). When averaged over the entire study, feed conversion ratio (FCR) was higher for gilts than for boars (2.76 v. 2.51, P = 0.013), was decreased by pST (3.05 v. 2.22, P &lt; 0.001), but unchanged by vaccination against GnRF (2.62 v. 2.65, P = 0.70). Fat deposition was lower in gilts than in boars (335 v. 378 g/day, P = 0.037), was decreased by pST treatment ((442 v. 271 g/day, P &lt; 0.001), and increased by vaccination against GnRF (333 v. 379 g/day, P = 0.026). In boars, fat androstenone was reduced by vaccination against GnRF (0.10 v. 2.47 μg/g, P &lt; 0.001) and tended to be reduced by pST (1.71 v. 2.44, P = 0.10), but only vaccination against GnRF reduced skatole (0.174 v. 0.050 μg/g, P &lt; 0.001). The combination of the treatments in all cases was at least additive, and in some cases synergistic. The concomitant vaccination against GnRF and treatment with pST affords an opportunity to increase growth rate and feed intake above control levels and above those of pigs treated with either treatment alone.

Metabolic and production responses to different porcine somatotropin injection regimes in pigs

Thirty-two female crossbred pigs (initial weight 75 kg) were used in this experiment to investigate the effect of differing porcine somatotropin (pST) regimes on growth performance. Pigs were kept in individual pens and fed ad libitum a wheat-based diet formulated to contain 14.4 MJ DE/kg and 180 g ideal protein/kg. Treatments were daily injection with saline (Sal), daily injection with pST (5 mg) (D), bi-daily injection with pST (10 mg) (2D), and injection with pST (12 mg) every Monday, Wednesday, and Friday (MWF). On the days that pigs were not receiving pST they were injected with saline (0.5 mL). All pST regimes caused a reduction (P &lt; 0.001) in feed intake and feed conversion ratio (FCR), although there was no significant effect on average daily gain. Feed intake decreased after the first injection and, for the D group, remained low and constant. Feed intake for the 2D group was also reduced but not to as great an extent as for the D group. Feed intake in the MWF group showed a clear temporal response, being low during the week but increasing over the latter part of the weekend. Thus, feed intake from Sunday until Monday mornings was 400 g greater (P &lt; 0.001) than from Saturday until Sunday mornings. Therefore, it appears that the effects of pST on feed intake may be reduced when a 3-day interval is used between injections. Back fat was significantly reduced with all pST injection regimes, whereas estimated fat deposition was only significantly reduced in the D and 2D pigs. Plasma urea nitrogen was increased, whereas glucose was decreased during pST administration and the average concentrations of both metabolites during the first week of administration were strongly related (P &lt; 0.001) to FCR over the full 3 weeks of the study (R = 0.733 and -0.683, respectively). Although daily injection with pST appears to give the greatest reduction in feed intake and fat deposition, an alternative pST injection regime involving less frequent pST injections can also improve growth performance similarly in finisher pigs.

The effect of genotype, sex and management strategy on the eating quality of pork

Two hundred and sixteen (Large White×Landrace×Duroc) crossbred pigs were used to determine the influence of genotype, sex, and management strategies on pork quality. The experiment was a 2×3×3 factorial design with the main treatments being genotype (A — 50% and B — <25% Duroc bloodline), sex (females, surgical barrows and immunological barrows) and management strategy (control — C, dietary conjugated linoleic acid supplementation — CLA, and porcine somatotropin administration — pST). Genotype A pigs had less backfat (P2 site), higher intramuscular fat percentage, higher muscle ultimate pH (pH u) and surface exudate, and the pork was tougher and less acceptable compared with Genotype B pigs. Female pigs had lower muscle pH u, higher surface exudate and tougher pork compared with both surgical and immunological barrows. Pigs fed the control diet had lower muscle pH u and higher surface exudate compared with pigs fed the CLA supplemented diet or administered pST. Pigs fed the control diet had higher consumer likeness scores for flavour, tenderness, juiciness and overall acceptability compared with pigs fed the CLA supplemented diet or administered pST. The results from this experiment indicate that pork eating quality is reliant on a complex interaction between genotype and sex. The results also indicate that management strategies such as pST administration and CLA supplementation, while being effective in reducing backfat, have the potential to have a negative impact on pork quality.

The Biology of Somatotropin in Adipose Tissue Growth and Nutrient Partitioning

During the past 20 years, much has been learned about how porcine somatotropin (pST) affects growth and nutrient partitioning in growing pigs. The development of techniques to produce large quantities of recombinantly derived pST enabled numerous long-term studies to be conducted in which the effects of daily pST administration could be evaluated. Collectively, these studies established that treatment of growing pigs with pST markedly stimulated muscle growth and, concurrently, reduced fat deposition. In growing pigs, maximally effective doses of pST increase average daily gain as much as 10-20%, improve feed efficiency 15-30%, decrease adipose tissue mass and lipid accretion rates by as much as 50-80% and concurrently increase protein deposition by 50%. These effects are associated with a decrease in feed intake of approximately 10-15%. These responses occur because pST has a wide array of biological effects that modulate nutrient partitioning between adipose tissue and skeletal muscle. The decrease in adipose tissue growth is due to a reduction in lipogenesis that is the consequence of pST blunting the effects of many insulin-dependent events. With respect to fatty acid synthase (FAS), a pace-setting enzyme in the lipogenic pathway, enzyme activity is markedly reduced by pST. This is the result of a pST-mediated decrease in FAS mRNA levels that occurs because FAS gene transcription is decreased. The consequence of the decrease in lipid synthesis is that adipocyte hypertrophy is impaired and, hence, tissue growth. This review will provide an overview of some of the biological effects of pST in adipose tissue and will discuss what is known about the underlying mechanisms that account for these effects.

Antihypertensive effect of a compound (PST 2238) that displaces ouabain from sodium pump in experimental hypertension

A major biologically active Na,K-ATPase inhibitor in the mammalian body may be ouabain-like compound (OLC). We investigated the contribution of OLC to high blood pressure (BP) in reduced renal mass-saline hypertension as a classical model of sodium-dependent hypertension. We used PST 2238 (PST), an orally active antiouabain agent, to block the action of OLC. First, the antihypertensive effect was examined in ouabain-induced hypertensive rats to confirm the antagonistic action of PST (10 mg/kg/day) against ouabain in vivo. Second, we tested the effect of PST in comparison with potassium canrenoate (100 mg/kg/day) on BP in established reduced renal mass (5/6)-saline hypertension in rats. Potassium canrenoate has been supposed to act partially as an ouabain antagonist and was used as a reference drug. Third, we compared the antihypertensive effect of PST on established reduced renal mass (4/6)-saline hypertension with those of potassium canrenoate and doxazosin mesylate (2 mg/kg/day). The continuous ouabain (100 μg/kg/day) infusion with osmotic minipump elevated BP after 4 weeks and a concomitant treatment with PST for 4 weeks abolished this rise in BP (P < 0.01). In rats with severe reduced renal mass-saline hypertension, PST administration for 2 weeks lowered BP (P < 0.01) to the same degree as potassium canrenoate. Also in rats with less severe reduced renal mass-saline hypertension, PST administration for 4 weeks reduced BP (P < 0.01) to the same degree as potassium canrenoate and doxazosin mesylate. These findings suggest that OLC may contribute to the elevated BP in reduced renal mass-saline hypertension and that PST may be an effective antihypertensive agent in several forms of hypertension characterized by increased OLC levels.

PROCESSING CHARACTERISTICS AND YIELD OF PORK FRANKFURTERS MANUFACTURED FROM GILTS ADMINISTERED EXOGENOUS PORCINE SOMATOTROPIN

ABSTRACT Eighteen gilts (75 kg) were injected daily with 0, 2.5, or 5 mg of porcine somatotropin (pST) for either 30 or 31 days prior to slaughter to examine the effects of dose of pST administration to swine on processing characteristics of frankfurters manufactured from pork. Frankfurters were manufactured from New York shoulders (NAMP #404) and formulated with fat from the same carcass to a final product target of 22% fat and 10% added water. Frankfurters from pST‐ treated gilts had lower smokehouse yields (0.9% decrease; P &lt;.005) and greater shear force peak height (35.4% increase; P &lt; 0.05) compared with the controls. The increased shear force required for skin failure of frankfurters manufactured from pork from pST‐treated pigs was not readily explained by other differences due to treatment (e.g., cooking stability, batter proximate composition or salt soluble protein content; all P &gt; 0.05)

Effects of porcine sometotropin on calcium and phosphorus balance and markers of bone metabolism in finishing pigs.

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.

Efficacy of chromium picolinate on performance and tissue accretion in pigs with different lean gain potential.

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.

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.

Combined pyridostigmine–thyrotrophin-releasing hormone test for the evaluation of hypothalamic somatostatinergic activity in healthy normal men

Pyridostigmine (PST), a cholinesterase inhibitor, induces a clear growth hormone (GH) release in man by suppression of hypothalamic somatostatin (SRIH). Somatostatin suppresses thyrotrophin (TSH) release in rats and men. Earlier studies showed that the thryotrophin-releasing hormone (TRH)-induced TSH response was not altered by 60-120 mg of PST. We studied whether a larger dose (180 mg) of PST can increase the TSH response to TRH. Six healthy young men were studied with the following six tests: (Test 1) 200 micrograms of TRH i.v.; (Test 2) 180 mg of PST po; (Test 3) three different doses of PST (60, 120, 180 mg) + TRH; (Test 4) 100 micrograms of octreotide (SMS) i.v.; (Test 5) SMS + TRH; (Test 6) PST + SMS + TRH. A large dose of PST (180 mg) significantly augmented GH, TSH and prolactin responses to TRH, while smaller doses of PST (60 and 120 mg) did not significantly increase the responses of GH and TSH. While the increased TRH-induced prolactin response by PST was not suppressed by SMS, the increased responses of GH and TSH were suppressed remarkably by SMS. Most of the subjects noticed a mild to moderate abdominal pain, nausea and muscular fasciculation after the administration of a large dose of PST administration. These data suggest that suppression of hypothalamic SRIH secretion by 180 mg of PST can augment the TSH response to TRH. However, the considerable side effects should be minimized before clinical application of the combined PST-TRH test.

Recombinant porcine somatotropin effects on sexual development and metabolic status of gilts

Prepubertal Yorkshire gilts (61.7 ± SD 3.7 kg) served as untreated controls (n = 8), were injected daily (at 15:00) for 28 d with 2 mg of porcine somatotropin (pST; n = 8), or were implanted with a prolonged-release (2 mg d−1 for 28 d) pST implant (n = 7). Gilts had ad libitum access to feed except during an overnight fast before blood sampling (06:00 to 22:00 h) on day 23 or 24. Feeding on day 23 or 24 resumed at 09:00 h and injected gilts received pST at 15:05 h. Gilts were slaughtered on day 28. Endogenous episodic ST secretion in both injected and implanted gilts was suppressed, but basal plasma ST in implanted gilts was elevated. Plasma insulin was elevated in response to pST injection and in implanted gilts postprandially, compared with controls. Plasma insulin-like growth factor I (IGF-I) was elevated in both injected and implanted gilts preprandially and postinjection. Plasma nonesterified fatty acids and creatinine were similar among groups. Urea nitrogen declined after feeding, and this decline was greater in injected than in implanted or control gilts. Basal episodic luteinizing-hormone (LH) secretion, reproductive-tract weight, follicular volume, and plasma and follicular-fluid estradiol-17β were similar among groups. However, follicular-fluid IGF-I concentrations were greater in injected and implanted, than control gilts. We conclude that pST administration (2 mg d−1) for 28 d significantly affected the ST–insulin–IGF–1 axis, but it did not affect LH secretion or reproductive-tract development. The pST-induced increase in follicular-fluid IGF–I may be of physiological significance to continued follicular development. Key words: Gilts, somatotropin, reproduction, metabolic status

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.

The effects of porcine somatotropin and dietary lysine on growth performance and carcass characteristics of finishing swine fed to 105 or 127 kilograms.

One hundred twenty barrows (initially 59 kg) were used to determine the effects of dietary lysine and porcine somatotropin (pST) on growth performance and carcass characteristics of finishing pigs fed to heavy market weights (127 kg). Pigs were injected daily with either 4 mg of pST or a placebo and fed diets containing either .8, 1.0, 1.2, or 1.4% lysine in a 2 x 4 factorial arrangement. Performance data were collected and evaluated for the weight ranges: 59 to 105, 105 to 127, and 59 to 127 kg. In addition, daily accretion rates of protein (DPA), lipid (DLA), moisture, and ash were determined by slaughtering six randomly selected pigs at the start of the experiment, then one pig per pen when pigs reached mean weights of 105 and 127 kg. Pigs injected with pST had greater (P < .05) ADG than control pigs at all weight ranges. Increased dietary lysine had no effect (P > .20) on ADG during the entire trial (59 to 127 kg). Although control pigs showed no increase in ADG with increasing lysine, ADG of pST-treated pigs tended to increase. This resulted in a pST x lysine interaction (P < .07) for ADG from 59 to 127 kg. Feed consumption decreased (P < .05) in pigs from 59 to 105 kg and 59 to 127 kg with pST treatment and with increasing dietary lysine. Feed conversion (G/F) was improved (P < .01) by pST administration and a tendency for a pST x lysine interaction (P < .12) was observed. At 105 kg, average backfat thickness, kidney fat, longissimus muscle area, and DPA were unaffected by dietary lysine but were improved by pST treatment (P < .01). At a slaughter weight of 127 kg, average backfat thickness decreased and DPA increased (linear, P < .05) with increasing dietary lysine and pST treatment (P < .01). Longissimus muscle area was increased and DLA was decreased (P < .01) by injections of pST but both were unchanged by dietary lysine. These data indicate that growth performance and carcass characteristics at 105 and 127 kg were improved by daily administration of 4 mg of pST. At both slaughter weights, increasing dietary lysine resulted in increased carcass leanness (increased carcass protein and decreased carcass lipid). Although increasing lysine did not improve overall (59 to 127 kg) ADG and feed efficiency, pST-treated pigs showed a greater response to increasing dietary lysine. The data indicate that pST-treated pigs (4 mg/d) require approximately 28 g/d of lysine.

The interrelationship of porcine somatotropin administration and dietary phosphorus on growth performance and bone properties in developing gilts.

Seventy-two gilts (initial weight = 57.9 kg) were used to determine the interrelationship of porcine somatotropin (pST) administration and dietary P on growth performance of finishing gilts (58 to 106 kg) and the effect on bone mechanical properties and mineralization for a 35-d postfinishing phase after withdrawal of pST administration. Gilts were injected daily with placebo (control) or 4 mg of pST and fed .4, .6, or .8% P in the finishing phase. Administration of pST increased ADG and G/F (P < .01) and decreased ADFI (P < .01) during the finishing phase. Increasing dietary P resulted in increased (quadratic, P < .04) ADG from d 0 to 28 of the finishing phase; however, dietary P had no effect (P > .18) on ADG, G/F, or ADFI for the overall finishing phase. When each block weight averaged 106 kg, half the gilts were slaughtered and the first rib, femur, and third and fourth metacarpals were collected. Stress, modulus of elasticity, and ash content of rib, femur, and metacarpals were reduced (P < .06) and femur wall thickness was increased (P < .01) in pST-treated gilts. Increasing dietary P increased (linear, P < .05) bending moment, stress, and ash content for all bones collected, with the exception of metacarpal stress, which was not affected (P > .22). The remaining 36 gilts were individually fed 1.8 kg/d of a common diet to assure a P intake of 22.8 g/d for the 35-d postfinishing phase. Gilts that received higher levels of dietary P during the finishing phase had increased (linear, P < .06) bending moment and ash content for the rib and femur; rib stress, and femur wall thickness were also increased after the postfinishing phase. From d 0 to 28 of the finishing phase, pST-treated gilts required a diet with > .4% P (10.3 g/d P) to maximize growth performance. However, a diet with .4% P (12.44 and 10.66 g/d P, control and pST-treated, respectively) was adequate for growth performance during the overall finishing phase (56 to 106 kg).(ABSTRACT TRUNCATED AT 400 WORDS)

Evaluation of long-term somatotropin implants in finishing pigs.

Ninety pigs were used to investigate the efficacy of long-term implants of porcine somatotropin (pST) in improving growth, feed:gain ratio, and carcass characteristics in pigs at three dose levels (0-, 100-, and 200-mg pST implant) from 71 to 99 kg live weight. The use of long-term implants did not alter (P > .05) growth rate. Administration of the 200-mg pST implant resulted in a 15% reduction in feed consumption, and this reduction was significant (P < .05). The feed:gain ratio was improved (P < .05) in pigs that received the 200- compared with 0-mg pST implant (3.2 vs 2.62 of kg feed/kg of gain). In pigs that received the 200- or 100-mg pST implant, there was a reduction (P < .05) in carcass weight; however, carcass length was similar (P > .05) regardless of pST treatment. Administration of the 200-mg pST implant resulted in 25 and 38% reductions (P < .05) in last rib fat and leaf fat compared with the 0-mg pST implant. The weights of kidneys and head were increased by the pST administration. The weights of wholesale cuts were not affected by the administration of the pST implant. However, separable skin and fat from the ham, loin, and picnic were lower (P < .05) in pigs that received the 200-mg pST than in pigs that received the 0-mg pST implant. Meat color and structure were similar across pST treatments, indicating that the use of long-term pST implants was not detrimental to meat quality.(ABSTRACT TRUNCATED AT 250 WORDS)