Effects Of Recombinant Porcine Somatotropin Research Articles

Effect of recombinant porcine somatotropin (rpST) on drug disposition in swine

Treatment of pigs with recombinant porcine somatotropin (rpST) causes a marked increase in feed utilization with increased weight-gain over untreated controls. Physiological parameters such as creatinine clearance were increased by rpST treatment. Clearance of drugs eliminated by hepatic extraction, like indocyanine green (ICG), were also increased by rpST treatment. However, clearance of intravenous (i.v.)-dosed propranolol (PPL) was not affected by rpST treatment and data from oral (p.o.)-dosing was inconclusive because of the low bioavailability, probably because of a high first-pass effect. The very low oral bioavailability indicates that intestinal metabolism of PPL is probably quite high. Analysis of urinary metabolites indicated production of the two phenolic isomers, but there was no metabolite corresponding to N-dealkylase activity; although the latter metabolite could have been eliminated in the bile with subsequent fecal elimination. PPL was an excellent in vitro substrate for measuring hepatic DME activity in vitro; two phenolic and one N-dealkylated metabolite were formed. The overall conclusions regarding this study must be that the effects of rpST on drug bioavailability and elimination were equivocal. As ICG and creatinine clearances were both increased significantly, one cannot rule out the probability that rpST would increase drug elimination in pigs as a result of increased hepatic uptake and/or renal clearance. One can only speculate that clearance of concurrently administered drugs would be increased. This would reduce residue levels, but it might also reduce efficacy.

Effect of recombinant porcine somatotropin on fetal and placental growth in gilts with reduced uterine capacity.

Crowded uterine conditions were induced by unilateral hysterectomy-ovariectomy (UHO) in 42 gilts to determine the effect of recombinant porcine somatotropin on fetal and placental growth. Gilts were randomly assigned across three replicates to one of three treatments: Control (C; n = 14), daily injections of 1 mL saline from d 0 to 64 of gestation, Early (E; n = 12), 5 mg of rpST/d from d 0 to 30, followed by 1 mL saline from d 31 to 64, and Late (L; n = 16), 1 mL saline/d from d 0 to 29, followed by 5 mg of rpST/d from d 30 to 64 of gestation. Blood was collected from each gilt via jugular venipuncture at d 0 and every 15 d thereafter. Gilts were hysterectomized on d 65 of gestation. Length of placental attachment and fetal crown-rump length were measured. Placentas and fetuses were weighed. Placental length, wet weight, and dry weight were recorded. Treatment with rpST (either E or L) increased (P < 0.0001) maternal plasma IGF-I concentrations relative to controls. Treatment with rpST did not affect placental wet weight or placental DNA content. However, E and L treatments increased the percentage of placental protein (P = 0.01) and placental dry matter (P = 0.10) and increased contact area of uterine-placental interface (P = 0.01). Despite changes in placental composition and morphology, weights of fetuses collected from L-treated gilts did not differ from controls, whereas weights of fetuses collected from E-treated gilts tended to be less than controls (P < 0.06). Administration of rpST increased maternal IGF-I concentrations and placental surface area but failed to increase fetal growth in the UHO model. Therefore, mechanisms that are independent of maternal IGF-I or placental contact area may control early fetal growth under crowded uterine conditions.

Influence of porcine somatotropin on the phosphorus requirement of finishing pigs: II. Carcass characteristics, tissue accretion rates, and chemical composition of the ham.

We investigated the effects of recombinant porcine somatotropin (pST) on the requirement for P to maximize lean tissue accretion and to minimize fat tissue accretion in two experiments using finishing pigs. Corn-soybean meal diets with varying levels of P were fed, and Ca was adjusted to maintain a Ca:P ratio of 1.1:1. In Exp. 1, 96 pigs were fed dietary P concentrations of .35, .45, and .65% from 75 to 109 kg BW. One-half of the pigs were injected daily with 4 mg of pST. Administration of pST increased (P < .05) percentages and accretion rates of lean tissue, bone, skin, water, and protein, but it reduced (P < .05) those of fat tissue and lipid. Increasing dietary P had little effect on chemical composition or accretion rates in untreated pigs, but it increased (P < .05) ash percentage and accretion in pigs treated with pST. Experiment 2 consisted of 66 pigs fed six dietary P concentrations (.35, .50, .65, .80, .95, and 1.10%) from 72 to 114 kg. One-half of the pigs were injected daily with 4 mg of pST. Percentages and accretion rates of lean tissue, bone, skin, water, and protein increased (P < .05) with pST, but those of fat tissue and lipid were reduced (P < .05). Increasing dietary P increased accretion rates of bone and skin (linear, P < .05), lean tissue, water, protein, and ash (quadratic, P <.05), and it reduced (quadratic, P < .05) that of lipid in pigs treated with pST. Dietary P level did not consistently affect percentages or accretion rates of tissues or chemical components in untreated pigs. In most instances, pigs treated with pST required higher dietary P levels and greater daily intakes of P to maximize lean tissue and protein deposition and to minimize fat tissue and lipid accretion than untreated pigs. These results indicate that finishing pigs treated with pST require higher dietary percentages of P to maximize carcass lean deposition as compared with untreated pigs.

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.

Effects of somatotropin and salbutamol in three genotypes of finishing barrows: blood hormones and metabolites and muscle characteristics.

We evaluated the effects of recombinant porcine somatotropin (pST) and the beta-adrenergic agonist salbutamol on plasam endocrine and metabolite profiles and muscle chemistry in three genotypes of growing barrows (n = 96, 139 d old). Treatments were in a 2 x 2 x 3 factorial arrangement, and main effects were pST (0 or 4 mg/d) and salbutamol (0 or 2.75 ppm); the three genotypes including purebred Meishan (M), 1/4 Duroc, 3/4 White composite (D x Wc), and 1/4 Meishan, 3/4 White composite (M x Wc). Individual pigs were injected daily with buffer or pST at 0700 and allowed ad libitum access to a corn-soybean meal diet (1.2% lysine) and water for 33 d. Plasma was obtained 4 h after injection and 3 h postprandially on d 0, 14, and 28 for determination of growth hormone (GH), insulin, IGF-I, glucose, urea N (PUN), NEFA, triglycerides, and cholesterol. Longissimus and semitendinosus samples were obtained, and protein, RNA, and DNA were quantified and loin chop shear force was measured. In general, plasma hormones and metabolites on d 14 and 28 were not affected by salbutamol in the absence of pST, although salbutamol tended to increase d 14 and 28 GH concentrations. Salbutamol lowered plasma IGF-I (d 14 and 28, P < .05), insulin (d 14, P < .01), and NEFA (d 28, P = .07) when pST was administered, although concentrations still exceeded those for control pigs. Salbutamol reduced (P < .05) IGF-I in M and M x Wc pigs, and GH was not changed in M pigs. Meishan pigs had a greater increase in glucose with pST than M x Wc or D x Wc pigs, although the effect was not consistent over time. Individual treatment with pST caused GH, insulin, IGF-I, glucose, NEFA, and triglycerides to be increased and PUN to be decreased on d 14 and 28. Cholesterol on d 14 and 28 was decreased by pST in M pigs, whereas no effects were found in the other genotypes. Muscle protein and RNA were increased by salbutamol and were consistently lowest for M pigs. Furthermore, pST did not affect muscle protein, but it increased RNA more in M pigs than in the others. Overall, pST and salbutamol seemed to act separately and by different mechanisms to alter muscle composition, but blood criteria generally representing fat metabolism (insulin, glucose, NEFA, triglycerides) were interactively affected. Meishan pigs tended to have greater changes in muscle and plasma composition with pST treatment than did M x Wc or D x Wc pigs.

Effects of recombinant porcine somatotropin on placental size, fetal growth, and IGF-I and IGF-II concentrations in pigs.

The objective of this study was to determine the effects of recombinant porcine somatotropin (rpST) on placental size, fetal growth, and maternal and fetal IGF-I and IGF-II concentrations. Twenty-four pregnant gilts received daily injections of either 1 mL of saline (control) (n = 12) or 5 mg of rpST (n = 12) from d 30 to 43 of gestation. Gilts were slaughtered on d 44 of gestation, reproductive tracts were removed, and fetal weight and length, placental weight, and implantation length were recorded. There was no effect of rpST on fetal or implantation length. Placental weight increased with rpST administration (71.20 +/- 3.52 vs 58.35 +/- 3.41 g; P < .02), as did fetal weight (18.06 +/- .55 vs 16.44 +/- .53 g; rpST vs control, respectively; P < .05). Implantation lengths were partitioned into quartiles to determine the effect of rpST on fetuses with different implantation lengths. The effect of rpST of fetal weight was greater in the first quartile ( < 137.5 mm) than in the fourth quartile ( > 240 mm) (16.04 vs 13.86 g compared with 19.47 vs 18.21 g, respectively). Analysis using a modified Brody curve suggests that the effect of rpST treatment on fetal weight is equivalent to the effect of increasing implantation length by 58.8 mm. Administration of rpST numerically raised IGF-I (P = .07) and IGF-II (P = .12) concentrations in fetal serum. Although maternal serum IGF-I concentrations were similar at d 30, treatment with rpST increased these concentrations over time (77.76, 247.75, 267.85 vs 82.59, 79.59, 77.97 ng/mL on d 30, 37, 43, respectively; P < .001, SE = 14.09). Maternal IGF-II concentrations were also similar at d 30 but decreased over time with rpST treatment (265.78, 219.61, 191.05 vs 285.44, 284.72, 283.05 ng/mL; P < .03, SE = 14.03). Increased maternal IGF-I concentrations may exhibit negative feedback on maternal IGF-II concentrations. The more pronounced effect of rpST on growth in fetuses with shorter implantation lengths suggests that rpST may increase uptake or utilization of nutrients by fetuses. In addition, nutrient transfer across placental membranes may be enhanced by rpST.

Effect of recombinant porcine somatotropin and monoclonal antibody directed to ovine somatotrophic hormone on nitrogen retention and immune parameters in pigs.

Single and combined effects of administration and withdrawal of recombinant porcine somatotropin (rpST) and an enhancing murine antiovine growth hormone monoclonal antibody (OA15) on nitrogen retention, and serological and immunological measurements in pigs were examined in a placebo-controlled experiment. Thirty-six barrows were allotted to one of four treatments: control, rpST, OA15, and OA15+rpST. The trial phase was four balance periods: a preperiod, two periods of treatment, and a postperiod. Weight- and nitrogen gain were higher for the rpST group by 13% (P < .01) and 15% (P < .001), for the OA15 group by 8% (P < .05) and 9% (P < .05), and for the OA15+rpST group by 25% (P < .001) and 20% (P < .001), respectively compared with the control group. During the postperiod, weight gain of the OA15- and the OA15+rpST group was 23% (P < .001) and 22% (P < .001) lower than that of the control group. Nitrogen gain during the postperiod was decreased by 19% (P < .01) for the OA15 group compared with the control group. Single or combined administration of rpST or OA15 did not affect (P > .10) cellular constituents in the blood of all groups during the periods of observation. Animals treated solely with rpST mounted a humoral immune response directed to rpST. This anti-rpST antibody response was, however, decreased (P < .01) in barrows treated with rpST and OA15 simultaneously. Also, a slight anti-rpST antibody response was noticed in barrows solely treated with OA15.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of different layers of joint cartilage from pigs treated with and without recombinant porcine somatotropin (rpST)

This study was undertaken to determine the concentrations of collagen and glycosaminoglycan (GAG) in different layers of joint cartilage of pigs. Effects of recombinant porcine somatotropin (rpST) treatment of pigs on cartilage composition was also examined. The results demonstrated that the concentrations of GAG uronic acid and collagen (measured as hydroxyproline) varied (P &lt; 0.05) between different layers and were reduced (P &lt; 0.05) by the rpST treatment. Key words: Osteochondrosis, articular-epiphyseal cartilage, hydroxyproline, glycosaminoglycan, recombinant porcine somatotropin, pigs

Effects of recombinant porcine somatotropin (rpST) on joint cartilage and axial bones in growing and finishing pigs

Seventy-two gilts (PIC, Cambourough) weighing 20 kg were allocated to four pens, each with two electronic feeders. After a 20-d conditioning period, eight pigs (two pigs/pen) were slaughtered for initial carcass measurements. The remaining pigs in each pen, at an average liveweight of 33.0 ± 2.49 kg (mean ± SD), were randomly assigned to three treatments: daily saline injection (control), daily injection of recombinant porcine somatotropin (rpST) (100 μg kg−1 liveweight) and a treatment group in which rpST injected pigs were switched to a saline injection at approximately 63 kg liveweight (withdrawal). Eight control and eight rpST-treated pigs, two from each pen were slaughtered at an average liveweight of 62.8 ± 3.72 kg, and the remaining pigs were slaughtered at 100.3 ± 5.51 kg. Daily injection of rpST increased the average concentration of plasma somatotropin but did not increase the width of distal ulna epiphysis. Vertebrae and ribs of pigs injected with rpST from 33.0 to 100.3 kg liveweight showed a higher water content (P &lt; 0.01), a lower ash content of moisture-free bone (P &lt; 0.05), and lower dry matter (P &lt; 0.01) and ash (P &lt; 0.001) densities than those of control pigs. Withdrawal of rpST injection at 62.8 kg liveweight abolished the effect of rpST on all bone properties except for the ash density. Injection of pigs with rpST from 33.0 to 100.3 kg resulted in higher (P &lt; 0.05) humeral condyle lesion score and decreased average concentrations of uronic acid (P &lt; 0.05) and hydroxyproline (P &lt; 0.005) in cartilage from both distal humeral and femoral condyles but had no significant effect on the ratio of uronic acid to hydroxyproline compared with control animals. Withdrawal of rpST treatment at 62.8 kg diminished the effect of rpST on cartilage soundness and uronic acid and hydroxyproline concentrations of the joint cartilage. The long-term use of rpST reduced chondrocyte metabolism, which may indirectly reduce compressive and tensile strength of cartilage and increase susceptibility to mechanical stress, leading to osteochondrosis. Key words: Osteochondrosis, growth rate, recombinant porcine somatotropin, bones, pigs

Rabbit growth, feed efficiency and body composition: Effects of recombinant porcine somatotropin

The effects of recombinant porcine somatotropin (rpST) were studied on rabbits from INRA 1077 strain, between the ages of 70 and 90 days. Ten rabbits received a daily intramuscular rpST injection (100 mg per day per kg of live weight) and were compared with ten control rabbits. Growth rate and feed efficiency were not affected by treatment. Perirenal fat deposits were smaller in rpST-treated than in the control rabbits (2·01 vs 2·72%) as were reference carcass lipid content (9·4 vs 10·8) and energy value (0·84 vs 0·88 MJ /100 g). The ratio between polyunsaturated fatty acids (FA) and saturated and monounsaturated FA was higher (0·32 vs 0·28). Reference carcass protein content was increased (20·5 vs 19·9%), as was the percentage of skin in slaughter weight (14·3 vs 13·4%). Muscular ultimate pH (24 h post mortem) was lower in the semimembranosus accessorius (5·67 vs 5·78) and in the biceps femmoris (5·65 vs 5·74) of treated rabbits. In conclusion, rpST, as a heterologous hormone, develops protein-rich tissues whilst lowering fat content and appears to affect the balance of muscular energy metabolism.

Fatty acid profiles, lipogenesis, and lipolysis in lipid depots in finishing pigs treated with recombinant porcine somatotropin.

Thirty-two pigs (average weight, 74 kg) were used to determine the effects of recombinant porcine somatotropin (rpST) and dietary CP concentration on carcass and noncarcass tissues. Pigs were injected intramuscularly with either rpST (50 micrograms.kg BW-1.d-1; n = 16) or vehicle (n = 16) at 0900 for 24 d. Half the treated and control pigs were given ad libitum access to either a 14 or 20% CP corn-soybean meal diet. The left side of the carcass was physically dissected into separable skin, soft tissues, and bone. Tissue samples were obtained for enzyme assays, proximate analysis, and fatty acid profiles. Proximate analysis (fat, water, protein) of adipose tissue (AT) samples indicated that rpST decreased the percentage of ether extractable lipid (P < .01) and increased the percentage of protein and water (P < .05, P < .01) in intermuscular (IM), subcutaneous (SC), and intrafascicular (IF) AT depots and slightly altered fatty acid profiles of longissimus muscle IF and SC AT. Fatty acid synthesis and malic enzyme activity were decreased by rpST (P < .01), suggesting that lipogenesis was decreased; however, lipolysis was unaffected. Pigs fed the high-CP diet (20%) had decreased AT malic enzyme activity (P < .05) and fatty acid synthesis (P < .05). Additionally, pigs fed the high-CP diet had greater kidney weights (P < .01). Heart, liver, and kidney weights were heavier (P < .01) in pigs treated with rpST, whereas skin and total bone weight were unaffected. Neither weights nor lengths of four individual long bones were affected by dietary protein concentration or administration of rpST.

Effect of Recombinant Porcine Somatotropin (rPST) Administration on Residual PST and Insulin-like Growth Factor-I Levels in Tissues and Sera of Pigs

The present study was conducted to examine the effects of recombinant porcine somatotropin (rPST) administration on residual PST and insulin-like growth factor-I (IGF-I) levels in various tissues and serum. Twenty-four crossbred barrows (average 61kg b. w.) were allocated to one of three treatments: 1) control (CONT) pigs received neither rPST nor vehicle, 2) sustained release-low dose (SR-L) pigs were treated twice at three-week intervals with 1, 000μg/kg b. w. (50μg rPST/kg b. w./day) by s. c. injection, 3) sustained release-high dose (SR-H) pigs were treated with 2, 000μg/kg b. w. (100μg rPST/kg b. w./day), as described in SR-L. Blood samples were taken on day 0 (prior to injection), day 28 (7 days post-injection), and day 41 (20 days post-injection). On day 42 (average 96kg b. w.), all experimental animals were killed for tissue sampling.Recombinant-PST administration did not elevate residual PST levels in the liver, kidney, injection area, longissimus muscle or backfat tissue. There was no difference in serum PST levels among treatments. No difference was found in IGF-I levels for all tissues studied among treatments. The serum IGF-I level of SR-L and SR-H group was higher in the day 28 sample, indicating that the serum IGF-I level remained elevated for at least a week after rPST injection. However the serum IGF-I level on day 41 (3 weeks after rPST administration) was the same for all treatments. These results suggest that, three weeks after rPST treatment via a sustained release form, there was no increase in residual PST and IGF-I levels in various tissues and serum.

Effect of recombinant porcine somatotropin on energy and protein utilization by growing pigs: interaction with capacity for lean tissue growth.

Three litters of four pigs from each of four different groups were used to evaluate the effect of porcine somatotropin (pST) on growth performance, body gain composition, energy and N metabolism, and in vitro cytochrome oxydase (final enzyme of the respiratory chain) activity of tissues. The four groups included boars from a synthetic line (SG1) or the Large White breed (SG2) and barrows from the Large White breed (SG3) or crossbred between Large White and Meishan breeds (SG4). Inherent capacity for daily lean tissue growth (LTG) decreased from SG1 to SG4. Within a litter, one pig was slaughtered and dissected at the beginning of the experiment (55 kg BW) and the three others were fed the same daily supply of protein and amino acids (26 g of lysine/d) but relative daily energy levels were either 113 (without pST: E1/0), 100 (3 mg of pST/d: E2/pST) or 87 (3 mg of pST/d: E3/pST). The 100 energy level corresponded to the ad libitum intake of E2/pST pigs. Two energy and N balances were carried out in respiration chambers during the experimental period. Pigs were slaughtered and dissected at approximately 95 kg BW and composition of gain was estimated using the comparative slaughter technique. In E1/0 pigs, daily BW, lean, and N gain were affected (P less than .01) by group; 566, 471, 374, and 315 g/d of lean tissue gain in SG1, SG2, SG3, and SG4 pigs, respectively. At high ME intake (E2/pST vs E1/0), pST increased daily BW (+14%), lean (+27%), or N (+26%) gain and reduced adipose tissue (-50%) gain, but the pST effect was inversely related to LTG: for N, the improvement was 2.8, 7.1, 7.0, and 11.1 g/d in SG1, SG2, SG3, and SG4 groups, respectively. Energy restriction (E3/pST vs E2/pST) reduced (P less than .001) adipose tissue gain in all groups but did not affect lean tissue or N gains in SG1, SG2, and SG3 pigs. In the pST-treated pigs of the SG4 group, the lean tissue or N gains were reduced (P less than .01) by energy restriction. Energy restriction combined with pST treatment (E3/pST) led to negligible amounts of fat deposited (40 g/d for SG1 + SG2 + SG3 pigs) and a gain:feed ratio higher than 500 g/kg (580 in SG1 pigs). The increased heat production measured in pST-treated pigs was due to its maintenance component: 275 vs 257 kcal of ME.kg BW-.60.d-1 (P less than .01).(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of recombinant porcine somatotropin and dietary protein on pancreatic digestive enzymes in the pig.

This study was conducted to determine the effect of daily recombinant porcine somatotropin (rpST) injection (0 or 120 micrograms/kg BW) and dietary CP level of the feed (14 or 26% CP) on pancreatic characteristics of growing pigs. Daily injection of rpST did not affect pancreatic weight (P = .885) but did decrease pancreatic amylase content (P = .005). The ratios of amylase:protein and amylase:trypsin were also lowered by daily rpST injection (P = .002 and P = .0002, respectively). There were protein x rpST and protein x rpST x sex interactions for the ratio of amylase:chymotrypsin. The CP content of the diet had a greater effect than the injection of rpST on pancreatic characteristics. Pigs consuming the 26% CP diet had significantly higher pancreatic weight (P = .003) and greater total pancreatic chymotrypsin (P = .006) than pigs consuming the 14% CP diet. The ratios of trypsin and chymotrypsin to DNA were also higher in pigs fed the 26% CP diet (P = .007 and P = .005, respectively). These responses were not influenced by sex. Recombinant porcine somatotropin seemed to have a slight effect on porcine pancreatic characteristics; however, dietary protein had a greater effect on pancreatic characteristics in market-weight hogs.

The effects of recombinant porcine somatotropin on reproductive function in gilts treated during the finishing phase

The objective of this study was to determine the effects of recombinant porcine somatotropin (rpST) treatment during the finishing phase on subsequent reproductive function in crossbred gilts. Forty gilts weighing 50 kg and housed in a swine finishing facility were randomly assigned to control or rpST treatment. Four control and four rpST-treated gilts were allotted per pen. Twenty rpST-treated gilts received 6 mg of rpST.gilt-1.d-1 in 1 ml of buffered carrier and 20 control gilts received 1 ml of buffered carrier.gilt-1.d-1. Injections were administered daily at 1400 in the extensor muscle of the neck. All gilts received an 18% CP diet containing 1.2% lysine. Treatment was terminated when the average weight in each pen reached 110 kg. Gilts treated with rpST gained more weight (P less than .05) than control gilts (59.8 +/- 1.0 vs 53.5 +/- 1.0 kg). Age at puberty was not different (rpST, 182.2 +/- 3.3; control 181.4 +/- 3.1 d). Prior treatment with rpST did not significantly affect length of estrus (rpST, 1.9 +/- .1; control, 1.8 +/- .1 d) or estrous cycle length (rpST, 20.6 +/- .4; control, 20.4 +/- .4 d). Ovulation rates at second estrus were similar for rpST gilts (15.1 +/- .5) and control gilts (14.4 +/- .5). More embryos (P = .10) were recovered on d 9 to 12 of gestation from rpST-treated gilts than from control gilts (13.1 +/- .9 vs 10.7 +/- .9).(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant porcine somatotropin: an immunotoxicology study1

The present study was designed to determine the effect of recombinant porcine somatotropin (rpST; 5, 15, or 25 mg.pig-1.d-1 for 57 d) on a variety of immune function variables. We observed no significant effect of rpST treatment on the gross pathology of the pigs, histopathology of the immune system organs, total and differential white blood cell counts, lymphocyte blastogenic response to mitogens, or the neutrophil functions of chemotaxis, ingestion, reduction of cytochrome C, iodination, and antibody-dependent cell-mediated cytotoxicity. Those variables that were significantly affected by rpST treatment include a decreased hemoglobin and packed red blood cell volume (at some time points for all three rpST dosages), a decrease in plasma protein level at the 25-mg dose, a small increase in neutrophil random migration (at all three rpST dosages), and a decrease in IgG antibody response to tetanus toxoid at 15 d after immunization (but not at d 8, 22, or 29). Additionally, rpST treatment was associated with a decreased rate of BW gain (at 15-mg dose), increased liver and kidney weights (at all three dosage levels), and an increased incidence of renal tubular cytoplasmic vacuolation of minor severity. There were no observed differences in the overall health of the pigs due to rpST treatment, based on clinical observations as well as determination of antibody titer to, and isolation of, common swine pathogens. Therefore, there was no evidence that the observed influence of rpST treatment on immune function would be clinically relevant.

Evaluation of recombinant porcine somatotropin on growth performance, carcass characteristics, meat quality, and muscle biochemical properties of Belgian Landrace pigs1

The dose related effects of recombinant porcine somatotropin (rpST) on growth, carcass characteristics, muscle properties, and meat quality were investigated in lean Belgian Landrace finishing pigs. Ninety-six pigs (48 barrows and 48 gilts) were injected daily with either vehicle, 1.5, 3, or 6 mg of rpST from 60 to 97.5 kg live weight. Each treatment group consisted of six pens of four pigs each (two of each sex). Pigs were given ad libitum access to a high-protein (20.4% CP) cereal-based diet. Administration of rpST increased (P less than .05) growth rate (16.3 to 25.4%) and improved (P less than .05) feed efficiency (16.9 to 29.4%). Feed consumption was reduced (12%; P less than .05) only in the 6 mg of rpST group. Liver, kidney, and heart weights were increased (P less than .05) in the 3 and 6 mg of rpST groups. Although the Belgian Landrace pigs are bred for superior carcass quality, rpST further improved (P less than .05) carcass composition at all dose levels as evidenced by a reduction (10 to 50%) in a number of subcutaneous fat depth measurements, an increase (10 to 20%) in longissimus muscle area, and an improvement in the lean cut:fat cut ratio. Rate of pH decline in the gluteus and longissimus muscles was similar, but rapid, in all groups (pH after 30 min = 5.74 to 5.94); the ultimate (24 or 72 h) pH was .15 to .2 pH units higher (P less than .05) in the pigs that received the 3 and 6 mg of rpST doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of recombinant porcine somatotropin on growth, feed intake and feed efficiency curves from 60 to 140 kg of pigs of three genotypes and two sexes

Curves for daily gain (DG), feed intake (FI) and feed efficiency (FE) of pigs treated with recombinant porcine somatotropin (rpST) were compared with curves of placebo-treated pigs from 60 to 140 kg live weight. The 48 animals included three genotypes (Duroc, Pietrain and Dutch Yorkshire∗ Dutch Landrace) and two sexes (barrows and gilts). From 60 kg onwards, half of the pigs were intramuscularly administered rpST (14 mg twice a week), and half received placebo. Pigs were fed ad libitum a diet containing 2162 kcal net energy and 182 g crude protein per kg. Differences in response to rpST between genotypes and sexes were investigated. The non-linear model y = a∗e −b∗W−c/W (where W is body weight and a, b and c are parameters) was fitted to weekly recorded data on DG, FI and FE. Beyond 100 kg live weight a declining response of DG to rpST was found in fatter pigs (Duroc, barrows). The response of FI was negative until about 90 kg and positive beyond 90 kg (except in Duroc). In leaner pigs (Pietrain, crossbreds, gilts), response to rpST was greater from 100 to 140 kg than from 60 to 100 kg. Response of FE was not greatly affected by body weight. It was concluded that, in rpST-treated pigs, DG reached a higher maximum at a higher live weight and that curves for DG, FI and FE are generally more persistent than in untreated pigs.

Pig weaning weight and changes in hematology and blood chemistry of sows injected with recombinant porcine somatotropin during lactation1

Weaning weight of pigs on d 18 to 21 of age was used to determine the effects of recombinant porcine somatotropin (rpST) on lactational performance of their dams. Crossbred Landrace x Yorkshire sows (n = 180, 202 to 270 kg BW) were assigned to receive daily i.m. injections of either 0, 8, or 16 mg of rpST on lactation d 7 to 20. Initially, injections of 16 mg of rpST/d caused 100% mortality (four sows); thus, a dose of 4 mg of rpST/d replaced 16 mg. Subsequently, 5 of 19 and 1 of 17 sows died in response to daily injections of 8 and 4 mg of rpST, respectively, resulting in termination of the experiment. Before termination, 48 sows (16 from each of the 0-, 4-, and 8-mg treatment groups) completed a lactation of 18 to 21 d in duration. Analysis of these data indicated that daily injection of lactating sows with rpST increased (P less than .05) weaning weight of pigs only if they were from litters that averaged greater than or equal to 2.6 kg/pig on lactation d 7. The BW of sows was decreased by rpST (P = .07). Subsequent experiments revealed 1) that rpST-induced death of lactating sows was caused from hemorrhaging of ulcers that developed at the pars esophagea, 2) that there was vacuolation of the liver and kidney of dead sows, and 3) that daily injection of 16 mg of rpST into nonlactating growing pigs (50 to 100 kg BW) for 28 d did not cause death or any observable illness in spite of 100% mortality of lactating sows after two to nine injections.

Effects of recombinant porcine somatotropin on metabolic rate in growing pigs

Effects of recombinant porcine somatotropin (rpST) on metabolic rate were studied in two trials with 24 crossbred barrows (Yorkshire x Landrace) in each. The barrows weighed about 80 kg (SE within trials 2.2 kg) at the start of the measurements and in each trial 12 pigs received 4 mg of rpST and 12 received a placebo. The diet contained 2.57 Mcal NE/kg and 20% CP (about 1% lysine). Animals were fed approximately 2.8 times maintenance (280 kcal ME.kg-.75.d-1). Heat production (gaseous exchange of CO2 and O2) and activity were measured continuously. Heat production associated with activity was calculated from the regression of heat production on activity. Animals treated with rpST exceeded controls in rate of gain by 252 g/d (P less than .001) and in metabolic rate by 14.5 kcal.kg-.75.d-1 (P less than .01). The rpST treatment increased rectal (+ .2 degrees C) and surface (+ .8 degrees C) temperatures. Activity-related heat production in treated pigs was increased, but this was only partly related to the increase in metabolic rate with rpST. The daily patterns of total and activity-related heat production were similar between pigs in both experimental treatments.