Somatotropin Administration Research Articles

Interrelationships between dietary lysine, sex, and porcine somatotropin administration on growth performance and protein deposition in pigs between 80 and 120 kg live weight.

Sixty male and 60 female crossbred pigs were allocated to an experiment to investigate the effects of porcine somatotropin (pST) administration (0 or 6 mg/d) and dietary lysine content on growth performance, tissue deposition, and carcass characteristics over the live weight range of 80 to 120 kg. Pigs receiving pST were given diets containing 6.9, 7.8, 8.8, 9.7, 10.6, or 11.5 g lysine/kg, whereas control pigs received diets containing 4.8, 5.8, 6.9, 7.8, 8.8 or 9.7 g lysine/kg. These dietary levels ranged from 0.40 to 0.70 g available lysine/MJ of DE for pST-treated pigs and from 0.28 to 0.58 g available lysine/MJ of DE for control pigs. Pigs were individually housed in pens, and there were five replicates of each treatment. All diets contained 14.5 MJ of DE/kg and were offered for ad libitum consumption to pigs between 80 and 120 kg live weight. Growth rate increased exponentially and food conversion ratio (FCR) decreased exponentially with increasing levels of lysine. In addition, there was a significant sex x pST interaction such that pST reduced the sex difference in FCR. Growth rate was faster in boars than in gilts and was increased by pST at the higher levels of dietary lysine. Similarly, FCR was lower for boars than for gilts and was decreased by pST at the higher dietary lysine levels. The optimum growth rate and FCR were defined as the lysine level at which growth rate and FCR were 95% and 105%, respectively, of the lysine plateau. The optimum growth rate and FCR were achieved at similar dietary lysine contents and were approximately 0.35 and 0.52 g available lysine/MJ of DE for control and pST-treated pigs, respectively. Protein deposition in the carcass increased exponentially with increasing dietary lysine level, was higher in boars than in gilts, and was increased by pST at the higher dietary lysine contents. Sex had no effect on dietary lysine required to maximize protein deposition. The dietary lysine contents required to ensure 95% of plateau protein deposition of 104 and 153 g/d were 0.39 and 0.55 g available lysine/MJ of DE for control and pST-treated pigs, respectively. The increase in lysine requirement with pST seems to be commensurate with the increase in protein deposition.

Effect of Bovine Somatotropin Administration on Day 11 after Artificial Insemination in Estrus-Induced Ewes during the Non-Breeding Season.

The present study aimed to examine the possibility that bovine somatotropin (BST) treatment after artificial insemination (AI) may improve the fertility by the stimulation of corpus luteum (CL) function in seasonally anestrous ewes. The experiment was conducted at the Tawa Field Station, Shibecha-cho in Hokkaido, Japan, during the non-breeding season (May, 1995). Eighty-nine mature (2 to 3 years old) Suffolk and Suffolk-crossed ewes were treated with controlled internal drug release devices containing 0.3 g progesterone (CIDR-G) for 12 days. Ewes were injected intramuscularly with 500 IU PMSG the day before CIDR removal. Eighty-seven ewes were assigned to an insemination of frozen semen on a fixed-time basis (42 to 50 h) after removal of CIDR. On the 11th day after AI (13 days after CIDR removal), 43 inseminated ewes were received 100 mg of recombinant BST, while the remaining 44 ewes were given vehicle as controls. The BST administration appeared to reduce pregnancy (65.1% vs. 72.7%) and lambing (51.2 vs. 65.9%) rates, prolificacy (145.5% vs. 165.5%) and proportion of ewes rearing more than two lambs (47.6% vs. 60.7%), as compared with controls, although there was no signifiant difference. BST-treated ewes had higher plasma GH concentrations (endogenous GH plus exogenous BST) at Day 19 (8 days after BST treatment) as compared with controls in both pregnant and non-pregnant ewes (P<0.05). Also, in the control group, plasma GH concentration of pregnant ewes was higher than that of non-pregnant ewes (P<0.05). Plasma progesterone (P) and estradiol-17β (E) cencentrations at Day 19 were lower in BST-treated ewes than that of control ewes (P<0.05). In conclusion, an administration with 100 mg of BST on Day 11 after AI during the non-breeding season resulted in the suppression of the ovarian function 1 week thereafter. Consequently, the conception rate and lambing rate did not improve by the present BST treatment in the ewe.

SENSORY CHARACTERISTICS AND PROCESSING YIELD OF BONELESS HAMS OBTAINED FROM GILTS ADMINISTERED EXOGENOUS PORCINE SOMATOTROPIN

ABSTRACT Two studies were conducted to evaluate effects of administration of porcine somatotropin (pST) to growing gilts on subsequent processing and sensory characteristics of porcine ham muscles. The Semimembranosus muscle was separated from the other major muscles prior to pumping to 120% of green weight with a brine solution. Treatment with pST in vivo increased the weight of Semimembranosus compared with controls (P &lt; 0.05). The muscle weight gains associated with pST treatment were retained during ham processing, resulting in heavier hams from gilts administered pST. However, pST treatment did not affect ham processing yields (%), smoked ham color, final product proximate composition or important palatability characteristics of hams (P &gt; 0.05).

Effect of Calcium Soaps of Fatty Acids and Administration of Somatotropin on Milk Production, Preovulatory Follicular Development, and Plasma and Follicular Fluid Lipid Composition in High Yielding Dairy Cows

The effect of fat and bovine somatotropin (bST) on preovulatory follicular hormones and lipids was evaluated by feeding cows for 150 d from parturition a control diet, a control diet plus 0.55 kg/d of calcium soaps of fatty acids, or a control diet with 500mg of bST injected every 14 d. Fourteen days after a synchronized or natural estrus, cows were injected with a PGF2α analogue; 48h later, follicular fluid from all ovarian follicles >8mm was aspirated. Cows fed fat or injected with bST produced more milk and milk solids than did control cows, and cows on the bST treatment lost more body condition after calving than did cows on the other treatments. Both treatments changed the proportion of estradiol-active follicles (>400ng of estradiol/ml of follicular fluid) and the correlation between follicular fluid estradiol concentration and the total number large follicles per cow. In follicles aspirated between 60 and 90 DIM the percentage of estradiol-active follicles was 67, 40, and 0 for cows on the control, calcium soaps of fatty acids, and bST treatments, respectively. After 90 DIM, no differences existed between treatments in the percentage of estradiol-active follicles. Estradiol concentration in follicular fluid was correlated with DIM at follicle aspiration (r=0.51). The proportion of oleic acid in free fatty acids in plasma at 50 DIM was lower in control cows and was lower in follicular fluid of estradiol-active follicles. Both calcium soaps of fatty acids and bST had a considerable effect on follicular development and activity and the composition of fatty acids in follicles.

Effects of Bovine Somatotropin and Evaporative Cooling Plus Shade on Lactation Performance of Cows During Summer Heat Stress

Thirty-two Holstein cows (8 per treatment) averaging 195 d in milk were assigned to 70 d of treatment on the basis of production during a 14-d pretreatment period, which was used for covariate analysis. The experiment was a randomized block design with a 2 × 2 factorial arrangement of treatments. Factors were normal shade or shade plus evaporative cooling with pressurized spray, plus with or without the administration of bovine somatotropin (bST). Cows receiving bST were injected with 500mg of bST every 14 d. All cows were fed the same total mixed rations twice daily at approximately 10% in excess of appetite, and water was offered free choice. There were no interactions between bST and the cooling system for any of the variables measured. Milk yield was increased by bST and tended to be greater for cooled cows. Fat percentages were increased by bST, and yields of fat, protein, and 3.5% fat-corrected milk, and the efficiency of conversion of dry matter to milk, whereas evaporative cooling increased body weights and protein yields, but decreased SNF and milk protein percentages. Rectal temperatures and respiration rates also were lower for cooled cows. And, bST increased nonesterified fatty acids in blood serum, suggesting that a part of the energy for increased milk production came from mobilization of body fat. Administration of bST effectively improved performance of cows under hot summer conditions whether evaporatively cooled or not.

Effects of exogenous somatotropin (ST) on gonadal function in ruminants and swine

During the past 15 years, many investigators have examined the effects of somatotropin (ST) on growth and lactation in farm animals. Throughout this period, concerns about potential effects of ST on reproduction have been expressed. The objective of the present review will be to focus on the effects of exogenous ST on the hypothalamic-pituitary-gonadal axis. Plasma progesterone is increased when recombinant bovine (rb)ST is given to cattle, early in lactation, and also to sheep. Also, the release of progesterone from cultured swine and human luteal cells is increased by ST. Treatment with rbSt increases the numbers of small follicles, but does not increase the ovulatory rate of ruminants. Doses of ST similar to those used to increase milk production do not affect the secretion of testosterone or spermatogenesis in rams or bulls. Stimulatory and inhibitory effects of exogenous ST on reproductive function of gilts have been reported. Daily injections of porcine ST (pST) delayed puberty and expression of estrus after puberty. Daily administration of pST increased the number of small follicles, but not of medium follicles, whereas administration of pST by using a sustained release implant increased the number of medium follicles. Size and weight of reproductive organs and concentration of testosterone are not affected when pST is administered for at least 42 d. However, pST enhanced testicular development and spermatogenesis when given to neonatal boars. In summary, administration of exogenous ST at doses known to alter milk production and carcass composition may have subtle positive and/or negative effects on the reproductive systems of cattle and swine; however, these effects appear to be transient.

Response of dairy ewes in late lactation to recombinant bovine somatotropin

This study was conducted to evaluate the effect of recombinant bovine somatotropin (rbST) administration to dairy ewes in late lactation on milk yield, composition, clotting parameters, and plasmin/plasminogen system. Eighty multiparous lactating Comisana ewes (186±18 days in lactation) were randomly assigned to one of two treatments: control and rbST. Slow-release rbST (120 mg/ewe) was administered for two injection cycles of 21 days each. Recombinant bovine somatotropin treatment increased milk (589.7 vs. 483.7 g/d; p < 0.01), protein (35.5 vs. 31.4 g/d; p < 0.05) and lactose (27.3 vs. 23.1 g/d; p < 0.05) yields. The percentage of milk fat (8.2% vs. 8.9%; p < 0.01) and protein (6.0% vs. 6.2%; p < 0.05) decreased, while somatic cells count and pH were unaffected by rbST treatment. Administration of rbST decreased milk coagulation time ( r) (12 vs. 13.1 min; p < 0.05), while firming rate ( k 20) and curd firmness ( a 30) were unaffected. Plasminogen activity of milk was lower in rbST-treated ewes (18.11 vs. 21.89 U/ml; p < 0.01).

Expression of growth hormone receptor 1A messenger ribonucleic acid in liver of dairy cows during lactation and after administration of recombinant bovine somatotropin.

The mRNA for growth hormone receptor is transcribed from at least three different promoters in cattle. The first promoter (P1) is liver-specific and transcribes growth hormone receptor mRNA containing exon 1A (growth hormone receptor 1A). The second and third promoters (P2 and P3) are active in a variety of tissues and transcribe growth hormone receptor mRNA containing exon 1B and 1C. The objective was to characterize P1 activity by measuring the amount of growth hormone receptor 1A mRNA in liver of dairy cows at different stages of lactation as well as after administration of recombinant bovine somatotropin (rbST). In study 1, liver RNA was isolated from Holstein cows during the dry period (nonlactating, n = 6) and during early (n = 6), mid (n = 6), and late (n = 11) stages of lactation. Six of the late-lactation cows received injections of rbST (25 mg/d) for 7 d prior to collection of liver tissue. In study 2, lactating Holstein cows received either no infusion (control, n = 10) or continuous infusion of rbST (29 mg/d, n = 10) for 63 d. The amount of growth hormone receptor 1A mRNA was decreased in early- and mid-lactation cows compared with late-lactation cows or nonlactating cows (study 1). Administration of rbST increased growth hormone receptor 1A mRNA (studies 1 and 2). The total amount of growth hormone receptor transcribed from alternative promoters (growth hormone receptor P2 and P3) remained unchanged during different stages of lactation or in response to rbST. We conclude that changes in liver growth hormone receptor mRNA in lactating dairy cattle primarily depend on growth hormone receptor P1 activity.

The effect of bovine somatotropin (bST) administration on reproduction, progesterone concentration during lactation and LH secretion during estrus, in dairy ewes

Twenty-two polytocous lactating Chios ewes were used to test the effects of bovine somatotropin (bST) on reproduction, progesterone concentration and LH secretion during estrus. Half of the ewes were injected every second week with 160 mg bST in a prolonged release vehicle, from the fifth day post partum until the end of lactation, while the remaining ones were used as controls. All animals were fed the same amount of ration. Supplementation with bST resulted in an increase of milk production (P<0.05) and an insignificant trend for delayed resumption of normal estrous cycles. Although there were no differences between groups, there was also a tendency for the bST group to display lower progesterone concentrations during the first three fortnights after the onset of normal estrous cycles and higher ones during the last three fortnights of the experiment, compared with the control group. Duration of the first normal luteal phase after delivery of the bST group was found to be shorter compared with the control group (P<0.05). After estrous synchronization the bST group showed a shorter estrus compared with the control group (P<0.05). Average and baseline LH concentrations during synchronized estrous in the bST group was lower (P<0.001) compared with the control group. Additionally, the conception rate did not differ between the two groups. This study supports the concept that the beneficial effects of bST treatment on milk production outweigh the potential deleterious effects on reproduction.

Biotechnology in animal nutrition, physiology and health

Biotechnology is already widely used in animal production and there are numerous other potential applications. Application of biotechnology can be envisaged for improving the performance of animals through better nutrition, enhanced production potential or improved health status. Nutrients (i.e. amino acids) can be produced and/or protected, resulting in improved formulation of diets that more accurately meet specific needs for productive functions. Enzymes can improve the nutrient availability from feedstuffs, lower feed costs and reduce output of waste into the environment. Pre- and pro-biotics or immune supplements can inhibit pathogenic gut microorganisms or make the animal more resistant to them. Plant biotechnology can produce crops with improved nutritional value or incorporate vaccines or antibodies into feeds that will cheaply and effectively protect the animals against diseases. Transgenic manipulation of commensal gut or rumen microorganisms has considerable potential for improving nutrition, gut development and health in animals. Administration of recombinant somatotropin (ST) results in accelerated growth and leaner carcasses in meat animals and increased milk production in dairy cows. The effects on meat or milk quality are limited. Immunomodulation can also be used for enhancing the activity of endogenous anabolic hormones. Transfer of the ST gene has the same effects as use of exogenous ST. However, unless the expression of the gene is controlled with ad-hoc promoters, the health status of the transgenic animals is severely impaired. There are numerous applications of biotechnology that aim to improve the health and welfare of animals. The generation of disease-resistant transgenic farm animals is still a long-term goal. On the other hand recombinant vaccines are widely in use. New advancements such as DNA-based vaccines and genetically engineered vaccine adjuvants hold much promise for improving animal health. Monoclonial antibodies and nucleic acid probes are used widely in diagnostic tools. Neutralization approaches, including immunological and antisense DNA, can offer interesting alternatives to surgical castration and the traditional prevention of broodiness in breeder birds. Acceptance of biotechnology in livestock production is difficult, and depends heavily on the perception of risks and benefits by the general public. Information is critically important in order that lay citizens can make an educated choice. The acceptance of biotechnology applied to animal production will depend on social and cultural aspects, and on the perceived benefits for consumers and society in general.

The effects of long-term administration of recombinant bovine somatotropin (Posilac) and Synovex on performance, plasma hormone and amino acid concentration, and muscle and subcutaneous fat fatty acid composition in Holstein-Friesian bull calves.

The effect of recombinant somatotropin (rbST), Synovex (Syn), and their combination (rbST+Syn) on intact male calves was examined in an experiment that lasted an average of 238 d. Holstein-Friesian bull calves were allotted to one of four subtreatments (n = 14/treatment) in a factorial arrangement. There were two levels of rbST (0; rbST) and two levels of the estrogenic growth promoter Synovex (0; Syn). The rbST was administered once every 2 wk as injections of 500 mg of Posilac. Synovex (C and S) was implanted at 90-d intervals. The animals were fed for ad libitum consumption a diet with a metabolizable energy concentration of 11.7 MJ/kg DM and 15% crude protein. The hot carcasses were weighed after the removal of kidney, pelvic, and cod fats, which were weighed separately. The 12th rib cut was saved for analysis. Average daily gain and feed conversion efficiency were increased by rbST treatment by 9% (P < .005) and 10% (P < .016), respectively. There was no significant effect of Syn treatment, nor was there a rbST x Syn interaction. The proportion of the fat of the large depots in the carcass was reduced by 34% (P < .0001) and in the longissimus muscle by 32% (P < .16) owing to the rbST treatment. The plasma concentrations of GH, insulin, and thyroxin were increased by rbST treatment (P < .001, P < .01, and P < .03, respectively). The concentration of IGF-I was not affected. Synovex had no effect on plasma hormone concentration. Plasma essential and nonessential amino acid concentrations were reduced by 14 and 9%, respectively, when rbST was injected. Concentrations of cholesterol and fatty acids in muscle and subcutaneous fat were not affected (P > .072) by the rbST treatment. Synovex increased the monounsaturated fatty acids (MUFA), and the combinaton of Syn with rbST reduced polyunsaturated fatty acid (PUFA) concentration in the longissimus muscle (at the 12th rib). The reduced muscle fat content of the rbST-treated animals was associated with a trend toward an increase in polyunsaturated fatty acids.

The effects of equine somatotropin (eST) on follicular development and circulating plasma hormone profiles in cyclic mares treated during different stages of the estrous cycle

The effects of exogenous equine somatotropin (eST) administration on ovarian activity and plasma hormone levels were evaluated on horse and pony mares. The objectives of this study were to determine the effects of eST on follicular development and circulating concentrations of leutinizing hormone (LH), estradiol, progesterone, and insulin-like growth factor I (IGF-I) in cyclic horse and pony mares. Sixteen mares received daily injections (im) of eST at a concentration of 25 μg/kg body weight on either Days 6 through 12 (Treatment A) or 13 through 19 (Treatment B) postovulation. In addition, contemporary mares were similarly given the carrier vehicle and served as controls (Treatments C and D). Blood samples were collected at 24-hr intervals and ultrasonographic evaluations were performed on the ovaries of each mare at 48-hr intervals beginning on the first day of treatment and ending either on the day of ovulation or 5 d postovulation. Circulating levels of insulin-like growth factor-I (IGF-I) were increased in treated mares by Day 3 post-treatment (P < 0.05). Also, mares in Treatment B exhibited a decrease in plasma estradiol concentrations (P < 0.05) when compared with control mares on Days 1 through 5 postovulation of the post-treated estrous cycle. In addition, circulating leutinizing hormone levels were different for mares in Treatment A compared with controls on Days −8 through −1 pre-ovulation (P < 0.05). All follicles present on the ovaries of each mare were measured and placed into one of five categories based on their diameter. Neither the mean number of follicles per size category ⩾8 mm in diameter nor the mean follicular diameter within each size category differed among treatment and control mares. However, eST treatment significantly increased the number of follicles ⩽7 mm on the ovaries of mares treated early in the estrous cycle when compared with control mares on Days 3 and 7 post-treatment and at the onset of standing estrus.

Effects of recombinant equine somatotropin on wound healing, carbohydrate and lipid metabolism, and endogenous somatotropin responses to secretagogues in geldings.

The primary purpose of this experiment was to assess the possible beneficial effects of recombinant equine somatotropin (reST) administration on wound healing in adult geldings. The effects of the 21-d reST treatment on carbohydrate and lipid metabolism and on endogenous ST characteristics were monitored as well. Single, full-thickness skin incisions (7.62 x 7.62 cm) were made in the pectoral region of all geldings on d 0. Treated geldings received reST at 20 microg/kg BW i.m., and control geldings received vehicle (10 mM sodium borate) at equivalent volumes daily from d 0 (immediately after surgery) through d 20. Tracings of the wounds were made with acetate transparencies, and wound areas were calculated via a digital analyzer. In addition to once-daily blood samples collected at specified days throughout the treatment period, an i.v. glucose tolerance test was performed on d 16, and three assessments of endogenous ST secretion were performed in the 2 d immediately following the end of treatment: epinephrine administration during the morning of d 21, an exercise test during the afternoon of d 21, and i.v. aspartic acid infusion on d 22. There was no effect (P > . 1) of reST treatment on wound healing as assessed by changes in wound areas. Daily plasma ST, IGF-I, glucose, and insulin concentrations were higher (P < .05) and urea-nitrogen concentrations were lower (P < .001) in geldings receiving reST relative to controls. Glucose, NEFA, and insulin concentrations were all higher (P < .01) in reST-treated geldings before glucose infusion on d 16, and the responses to glucose were greater (P < .05) as well. Epinephrine administration increased (P < .02) ST concentrations in control geldings on d 21 but not in reST-treated geldings; a similar suppressive effect of reST treatment was observed for the ST response to exercise (P < .001). After aspartic acid infusion on d 22, reST-treated geldings had a much smaller (P < .001) ST response than did control geldings. In conclusion, reST administered to geldings at 20 microg/kg BW i.m. caused hyperglycemia, hyperinsulinemia, insulin insensitivity, mobilization of fatty acids, and an apparent negative feedback on the pituitary's ST response to various stimuli known to induce ST secretion. However, there was no beneficial effect of reST treatment with the wound model used in this experiment.

The effects of porcine somatotropin administration and gender on cooking properties and palatability attributes of pork muscle

Loin roasts and ham steaks from 120 Yorkshire pigs (60 barrows and 60 gilts) were utilized to evaluate the effects of porcine somatotropin (PST) treatment and gender on cooking properties and palatability attributes. Within each gender, pigs were randomly allocated to the following three treatments: 1) control, 2) prolonged-release PST implants (2 mg d−1), or 3) daily subcutaneous PST injections (2 mg d−1). All animals received a 17% crude protein diet, ad libitum. Animals received PST treatments within a body weight range of 70 ± 5 kg to 96 ± 5 kg. All animals were slaughtered and processed using simulated commercial procedures. Longissimus lumborum (loin) roasts (lumbar) and cured and smoked semimembranosus (SM) steaks were roasted to 75 and 60 °C, respectively, in a 177 °C oven, sub-sampled, and evaluated by an eight-member sensory panel. No differences in cooking properties or palatability attributable to gender were observed (P &gt; 0.05). However, cured and smoked SM steaks from pigs receiving daily PST injections were more tender both initially and overall (P &lt; 0.05) than their counterparts from control pigs. In addition, cured and smoked SM steaks from pigs receiving daily PST injections had less perceived connective tissue (P &lt; 0.05) than their counterparts from control pigs and pigs receiving prolonged-release PST implants. The cooked loins from pigs receiving prolonged-release PST implants were perceived to contain less connective tissue than their counterparts from control pigs and pigs receiving daily PST injections (P &lt; 0.05), but cooked loins from pigs receiving prolonged-release PST implants had less-desirable flavour (P &lt; 0.05) than their counterparts from pigs receiving daily PST injections. It should be noted, however, only the tenderness differences observed in the cured and smoked SM were of sufficient magnitude to be of practical importance. Consequently, it would appear PST treatments, particularly daily injections, can be utilized to achieve previously reported, potential production and carcass composition advantages, while possibly improving the eating quality of some pork products. Key words: Pork, somatotropin, PST, gender, cooking properties, palatability attributes

Decreased Glucose Response to Insulin is Maximal Within 24 Hours of Somatotropin Injection in Growing Pigs

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

Effects of long-term recombinant bovine somatotropin (bST) administration on milk yield, milk composition and mammary gland health of dairy ewes

The present investigation was carried out to test the effects of recombinant bovine somatotropin (bST) on galactopoiesis and mammary gland health of the ewe. Twenty-two polytocous lactating Chios ewes were assigned into two groups (11 in control group and 11 in treatment group). Treated ewes were injected every second week with 160 mg bST in a prolonged release formulation, from the fifth day after delivery until the end of lactation. All animals were fed the same ration. Supplementation with bST significantly ( P<0.05) increased the 6% FCM (22.21% over the controls) without changing the duration of the lactating period. Fat and protein content of milk (%) increased ( P<0.05) and lactose content (%) decreased ( P<0.05) as lactation progressed in both groups. Differences in the above mentioned contents between groups were not significant ( P>0.05). Mean Somatic Cell Count (SCC) from animals without subclinical mastitis were progressively increased ( P<0.05) from weaning to the end of lactation in both groups, but the mean SCC from the bST group were found to be higher compared with that of the control group. This difference was significant ( P<0.05) only after the eighth fortnight after delivery. Differences between groups concerning the prevalence of bacteriologically positive milk samples were not significant ( P>0.05). Coagulase-negative staphylococci were the predominant organisms isolated from milk samples in both groups. Prevalence of subclinical mastitis was unaffected after bST administration ( P>0.05) although treated animals tended to show higher rates.

Chronic recombinant equine somatotropin (eST)administration does not affect aerobic capacity or exercise performance in geriatric mares

The purpose of this experiment was to test the hypothesis that chronic (89 days) administration of recombinant equine somatotropin (eST) would increase aerobic capacity and improve exercise performance in old mares. Fifteen, healthy, unfit, aged (20-26 year old) mares were randomly assigned to a treatment (eST, 12.5 mg day-1 in 3 ml glycine/manitol buffer, s.c., n = 7) or control (vehicle, 3 ml day-1, s.c., n = 8) group. Aerobic capacity and exercise performance were measured using a standardized exercise test (SET) performed on a high speed treadmill. Tests were conducted before (-21 days), during (+43 days and +89 days) and after (+127 days) treatment. During the SET, resting data were collected and the horses then ran up a fixed 6% grade, starting at 4 m s-1, with a 1 m s-1 increase every 60 s (omitting 5 m s-1) until fatigue. Oxygen uptake (VO2) was measured using an open flow calorimeter and blood lactate concentration (LA) via a lactate analyser. Venous blood samples (10 ml) were collected at rest, during the last 10 s of each step of the SET, and after exercise and used to measure LA, plasma protein concentration (PP), hematocrit (HCT), and the plasma concentrations of creatine kinase (CK) and aspartamine transferase (AST). There were no differences (P > 0.05) in resting VO2, LA, TPP, or HCT due to treatment or test time. Furthermore, there were no differences (P > 0.05) in maximal oxygen uptake (VO2max), top run velocity, run time, watts at VO2max, velocity to produce a lactate of 4 mmoll-1 (VLA4), watts at VLA4, peak HCT or peak LA. Finally, there were no differences (P > 0.05) in resting or post-exercise CK or AST. These data indicate that chronic eST administration does not affect aerobic capacity or indices of exercise performance in unfit aged mares.

Recombinant bovine somatotropin (rbST) administration to creep-fed beef calves increases muscle mass but does not affect satellite cell number or concentration of myosin light chain-1f mRNA.

Our objective in this study was to determine the effect of recombinant bovine somatotropin (rbST) on indices of muscle development in creep-fed beef calves. Crossbred steer calves were assigned to one of two treatment groups: control (sham-injected; n = 12) or rbST-treated (.09 mg x kg(-1) x d(-1); n = 12). Calves were injected every 14 d starting at d 28 of age and were weaned at 205 d of age. Supplemental creep feed was supplied free access to all calves to compensate for an expected increased protein and energy requirement in calves given rbST. Biopsy (d 100) and slaughter (d 206) samples of semitendinosus muscle were evaluated for satellite cell, myofiber nuclei numbers, and myosin light chain (MLC-1f) mRNA quantification. Myofiber nuclei and satellite cell numbers per 100 myofibers and MLC-1f mRNA:rRNA ratios at 100 and 206 d of age were not different (P > .10) between control and rbST-treated calves. Total gain, ADG, quality grade, femur length, percentage kidney, pelvic, and heart fat, dressing percentage, plasma IGF-I, and plasma urea nitrogen concentrations did not differ (P > .10) between control and rbST-treated calves. However, rbST-treated calves had larger longissimus muscle areas (P < .03), less marbling (P < .001), higher carcass conformation scores (P < .04), greater mass of separated muscle (P < .03), more ground meat (P < .01), and heavier carcass weights (P < .05) than control calves. Thus, rbST treatment increased muscle characteristics while nuclei number and MLC-1f mRNA concentrations remained the same, implying that the additional muscle growth was in a normal fashion.

Administration of Recombinant Bovine Somatotropin to Dairy Cows for Four Consecutive Lactations

Effects of long-term administration of recombinant bovine somatotropin (bST) to dairy cows on complete lactational performance [60 (±3) to 284 (±3) d in milk (DIM)] were studied for four consecutive lactations. Beginning on d 60 (±3) postpartum, Holstein cows received biweekly injections (500mg) of bST (n=39) or a placebo (control; n=39) during the first lactation of the study. Cows either continued on the same treatment (n=26) or were switched to the opposite treatment (n=29) during the second lactation. Cows that changed treatments were injected for only 16 wk during the second lactation. Six cows per treatment completed four consecutive lactations. Treatment with bST during the first lactation did not have a residual effect on milk yields during the second lactation. Injections of bST during the second lactation increased milk yield 6.5 kg/d from 60 (±3) to 172 DIM. For the four lactations, cows receiving bST yielded 3.7kg/d (14%) more milk and gained 52kg (37%) more body weight than did controls. Pretreatment (from 0 to 56 DIM) milk yields in yr 2, 3, and 4 were not affected by previous bST treatment. Milk yield, efficiency of feed utilization, and body weights were enhanced in cows injected with bST for four consecutive lactations. Previous bST treatment did not diminish milk yields in subsequent lactations.

Effect of Calcium Soaps of Fatty Acids and Administration of Somatotropin in Early Lactation on Productive and Reproductive Performance of High Producing Dairy Cows

This study examined the mechanisms by which calcium soaps of fatty acids and bovine somatotropin (bST) affect production and reproduction of high producing cows. Calcium soaps of fatty acids were fed at 2.2% dry matter, and 500mg of Zn-sometribove (Monsanto Inc., St Louis, MO) were injected subcutaneously every 14 d from 10 to 150 d in milk (DIM).Production of fat-corrected milk was increased by 3.5 kg/d when calcium soaps of fatty acids were fed, by 6.1 kg/d when bST was administered, and by 7.4 kg/d when calcium soaps of fatty acids were fed and bST was administered. Body weight was similar for cows on all treatments until 85 DIM after which cows that were treated with bST had lower body weights. Body condition scores decreased more for cows treated with bST and began increasing later and more slowly. Treatment with bST resulted in more cows that experienced first ovulation after 30 DIM, and more cows on the control treatment exhibited first estrus before 35 DIM. Days open were greater when bST was administered. After the first artificial insemination, conception rates were similar for cows on the control treatment and for cows fed calcium soaps of fatty acids; conception rates after the first artificial insemination were low for all cows treated with bST. Pregnancy rates at 120 and 150 DIM were decreased by bST.Number of DIM to first ovulation, number of DIM to first estrus, and days open were negatively correlated with glucose and cholesterol concentrations in plasma. Production of fat-corrected milk was correlated with days open and with concentrations of triglycerides in plasma, nonesterified fatty acids, and cholesterol. Increased production had different effects on reproduction when induced by calcium soaps of fatty acids or bST treatment. Some of the adverse effects of bST treatments were alleviated by calcium soaps of fatty acids.