Reproductive and growth responses of gilts to exogenous porcine pituitary growth hormone

Forty gilts (mean wt = 72 kg) were administered daily either vehicle (C = control) or 70 micrograms porcine growth hormone (pGH)/kg BW. After 30 d of treatment, eight gilts per group (Exp. 1) were slaughtered and blood, uteri and ovaries were collected. Follicular fluid (FFl) was collected and granulosa cells (GC) were cultured. The remaining gilts (Exp. 2) were treated for up to 35 additional days and examined twice daily for estrus. Estrusal gilts were removed from the experiment. Noncyclic gilts (n = 9 of 12 pGH; n = 4 of 12 C) were slaughtered on d 66 and their ovaries were examined. Ovarian weights were not different for pGH and C gilts in either Exp. 1 (P greater than .1) or Exp. 2 (P = .09). Uterine weights were greater for pGH-treated than for C gilts (P less than .007) in Exp. 1, but not in Exp. 2. Concentrations of estradiol (E2) in plasma and FF1 and of progesterone (P) in plasma and FF1 were not different for pGH and C gilts. Concentrations of insulin-like growth factor-I (IGF-I) in FF1 and in serum were greater for pGH than for C gilts (P less than .01). Concentration of P in serum-free medium of cultured GC was lower for GH than for C (P less than .05) in the presence or absence of gonadotropins in Exp. 1. The FSH-stimulated secretion of P was also lower for GC of pGH-treated gilts in Exp. 2, indicating a failure of GC to differentiate in culture. Only one pGH gilts in Exp. 2 manifested estrus, compared with seven C gilts (P less than .025). In Exp. 1, ADG was higher (P less than .03) and feed/gain lower (P less than .07) for pGH gilts. Longissimus muscle area (LMA) was not different (P = .19) between groups. Backfat thickness (BF) was lower (P less than .005) in pGH than in C in both Exp. 1 and 2. We conclude that exogenous pGH increased growth rate, improved feed efficiency and altered carcass traits in gilts. However, these effects were associated with impaired ovarian development of prepubertal gilts and a low incidence of estrus.     

Interrelationships between sex and exogenous growth hormone administration on performance, body composition and protein and fat accretion of growing pigs

Forty-five pigs with an average initial live weight of 60 kg were used to investigate the effects of daily exogenous porcine pituitary growth hormone administration at two dose levels (pGH; 0, excipient buffer injected, and 100 micrograms.kg-1.d-1) for a 31-d period on the performance and body composition of boars, gilts and barrows allowed to consume feed ad libitum. Excipient boars consumed less feed, exhibited faster and more efficient growth (P less than .01) and produced less fat and more protein and water (P less than .01) in the empty body compared with excipient barrows, which in turn contained more fat and less water (P less than .05) in the empty body than did excipient gilts. These differences were largely eliminated by pGH administration, which induced differential effects in growth performance and body composition in boars, gilts and barrows. Growth hormone administration improved growth rate by 13, 22 and 16% and feed conversion efficiency by 19, 34 and 32% in boars, gilts and barrows, respectively. The reduction of body fat content (g/kg) elicited by pGH was 22, 36 and 33% for boars, gilts and barrows, respectively, with a corresponding increase (P less than .01) of body protein and water content. The magnitude of the pGH responses was greatest for gilts and barrows compared with boars, negating intrinsic sex-effect differences in growth performance and body composition of pigs. Pigs used in this study and treated with pGH exhibited a rate of protein deposition (approximately 225 g/d) far greater than previously reported, and as such redefine the genetic capacity for lean tissue growth by the pig.     

Effect of constant versus adjusted dose of exogenous porcine growth hormone (pGH) on growth and reproductive characteristics of gilts

Growth, carcass traits, and selected reproductive characteristics were evaluated in prepubertal gilts treated with either a constant mass of pGH or a mass of pGH adjusted periodically for changes in BW. Gilts (64 kg, n = 24) were given 24 daily injections of either vehicle (C; control) or one of two doses of pGH: 70 micrograms/kg of BW, with dose adjusted every 5th d for changes in BW (A; adjusted), or 70 micrograms/kg of initial BW (U; unadjusted). Gilts were slaughtered on d 25. Gilts treated with pGH had higher ADG (P less than .002) and improved feed efficiency (kg of feed/kg of gain; P = .0003) compared with controls. Weights of adrenal glands, liver, heart, and kidney were higher (all P less than .01) for Groups A and U than for Group C gilts. Average backfat thickness was less (P less than .004) for A and U gilts than for C gilts and less for Group A than for Group U (P less than .02). Furthermore, growth and carcass traits were similar (P greater than .05) for Groups A and U, except for measurements of first rib backfat, last rib backfat, and average backfat depth (P less than .05). Culture of granulosa cells (GC) was employed to assess ovarian function. Addition of FSH to the culture media enhanced secretion of progesterone (P4) by cultured GC from all in vivo treatments compared with unsupplemented cultures of GC (P less than .05). Addition of LH to the culture media enhanced secretion of P4 by cultured GC from pGH-treated gilts only (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of dietary L-carnitine on growth performance and body composition in nursery and growing-finishing pigs.

Two experiments were conducted to determine the effect of dietary L-carnitine on growth performance and carcass composition of nursery and growing-finishing pigs. In Exp. 1,216 weanling pigs (initially 4.9 kg and 19 to 23 d of age) were used in a 35-d growth trial. Pigs were blocked by weight in a randomized complete block design (six pigs per pen and six pens per treatment). Four barrows and four gilts were used to determine initial carcass composition. L-Carnitine replaced ground corn in the control diets to provide 250, 500, 750, 1,000, or 1,250 ppm. On d 35, three barrows and three gilts per treatment (one pig/block) were killed to provide carcass compositions. L-Carnitine had no effect (P > 0.10) on growth, percentages of carcass CP and lipid, or daily protein accretion. However, daily lipid accretion tended to decrease and then return to values similar to those for control pigs (quadratic P < 0.10) with increasing dietary L-carnitine. In Exp. 2, 96 crossbred pigs (initially 34.0 kg BW) were used to investigate the effect of increasing dietary L-carnitine in growing-finishing pigs. Pigs (48 barrows and 48 gilts) were blocked by weight and sex in a randomized complete block design (two pigs/pen and eight pens/treatment). Dietary L-carnitine replaced cornstarch in the control diet to provide 25, 50, 75, 100, and 125 ppm in grower (34 to 56.7 kg; 1.0% lysine) and finisher (56.7 to 103 kg; 0.80% lysine) diets. At 103 kg, one pig/pen was slaughtered, and standard carcass measurements were obtained. Dietary L-carnitine did not influence growth performance (P > 0.10). However, increasing dietary carnitine decreased average and tenth-rib back-fat (quadratic, P < 0.10 and 0.05), and increased percentage lean and daily CP accretion rate (quadratic, P < 0.05). Break point analysis projected the optimal dosage to be between 49 and 64 ppm of L-carnitine for these carcass traits. It is concluded that dietary carnitine fed during the nursery or growing-finishing phase had no effect on growth performance; however, feeding 49 to 64 ppm of L-carnitine during the growing-finishing phase increased CP accretion and decreased tenth-rib backfat.     

Stimulation of pig growth performance by porcine growth hormone and growth hormone-releasing factor

The current study was undertaken to determine the effects of human growth hormone-releasing factor [hpGRF-(1-44)-NH2] on growth performance in pigs and whether this response was comparable to exogenous porcine growth hormone (pGH) treatment. Preliminary studies were conducted to determine if GRF increased plasma GH concentration after iv and im injection and the nature of the dose response. Growth hormone-releasing factor stimulated the release of pGH in a dose-dependent fashion, although the individual responses varied widely among pigs. The results from the im study were used to determine the dose of GRF to use for a 30-d growth trial. Thirty-six Yorkshire-Duroc barrows (initial wt 50 kg) were randomly allotted to one of three experimental groups (C = control, GRF and pGH). Pigs were treated daily with 30 micrograms of GRF/kg body weight by im injection in the neck. Pigs treated with pGH were also given 30 micrograms/kg body weight by im injection. Growth rate was increased 10% by pGH vs C pigs (P less than .05). Growth rate was not affected by GRF; however, hot and chilled carcass weights were increased 5% vs C pigs (P less than .05). On an absolute basis, adipose tissue mass was unaffected by pGH or GRF. Carcass lipid (percent of soft-tissue mass) was decreased 13% by GRF (P less than .05) and 18% by pGH (P less than .05). Muscle mass was significantly increased by pGH but not by GRF. There was a trend for feed efficiency to be improved by GRF; however, this was not different from control pigs. In contrast, pGH increased feed efficiency 19% vs control pigs (P less than .05). Chronic administration of GRF increased anterior pituitary weight but did not affect pituitary GH content or concentration. When blood was taken 3 h post-injection, both GRF- and pGH-treated pigs had lower blood-urea nitrogen concentrations. Serum glucose was significantly elevated by both GRF and pGH treatment. This was associated with an elevation in serum insulin. These results indicate that increasing the GH concentration in blood by either exogenous GH or GRF enhances growth performance. The effects of pGH were more marked than for GRF. Further studies are needed to determine the optimal dose of GRF to administer in growth trials and the appropriate pattern of GRF administration in order to determine whether GRF will enhance pig growth performance to the extent that exogenous pGH does.     

Effect of treatment with and subsequent withdrawal of exogenous porcine somatotropin on growth and reproductive characteristics of gilts

Two experiments were conducted to examine responses of gilts to treatment with and withdrawal of exogenous porcine somatotropin (PST). In Exp. 1, 36 prepubertal gilts (79.7 +/- .9 kg; 159.1 +/- .7 d) were allotted randomly to receive daily either 0 micrograms PST (C) or 70 micrograms PST/kg initial BW for either 21 (PST-3) or 42 d (PST-6). Gilts were examined for estrus daily by a mature boar starting on d 22 and continuing for up to 50 d. Gilts that expressed estrus were mated and removed from treatment. PST-treated gilts had higher ADG (P less than .01) and lower feed/gain (P less than .02) than C gilts. Following initiation of boar exposure, C gilts (mean interval to estrus = 2.0 d) exhibited estrus earlier than PST-3 (24.8 d) and PST-6 (24.0 d) gilts (P less than .07); however, only two C gilts were observed in estrus compared with six PST-3 and six PST-6 gilts. In Exp. 2, 40 prepubertal gilts (72.6 +/- 1.0 kg; 141.1 +/- .7 d) were allotted randomly to receive daily either 0 mg PST (C) or 5 mg PST for 30 d. On d 31, half the gilts were comingled with unfamiliar penmates and examined for estrus daily by a mature boar for up to 45 d. Estrual gilts were removed from treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interaction of dietary protein content and exogenous porcine growth hormone administration on protein and lipid accretion rates in growing pigs

Sixty-six intact male pigs were used to investigate the relationships between exogenous porcine growth (pGH) administration (0, excipient-treated, and .09 mg recombinant pGH.kg-1.d-1) and dietary protein content (8.3, 11.4, 14.5, 17.6, 20.7 and 23.8%) on protein and lipid accretion rates over the live weight range of 30 to 60 kg. Feed intakes were restricted (1.84 kg.pig-1.d-1) and pGH was administered daily by i.m. injection. Rate of protein deposition increased with increasing dietary protein up to 17.6 and 20.7%, respectively, for control and pGH-treated pigs; both growth and protein deposition were enhanced by pGH on the four higher protein diets but remained unaffected by pGH administration to pigs given the two lowest protein diets. Plasma IGF-I concentration was elevated by pGH administration in pigs given the four higher protein diets but unaffected by pGH with the two lowest protein diets. Rate of fat deposition was depressed on all dietary protein treatments by pGH administration; carcass fat content of control and pGH-treated pigs declined with each increase in dietary protein up to 17.6 and 23.8%, respectively. The results demonstrate that pGH acts independently on protein and lipid metabolism.     

Effects of gender and genotype on the response of growing pigs to exogenous administration of porcine growth hormone

Sixty crossbred pigs (Large White x Landrace) were used in a 2 x 2 x 2 factorial experiment to investigate the effects of gender (intact males vs females) and strain (A vs B) on the response to exogenous porcine growth hormone (pGH) administration (0 [excipient-treated] vs .1 mg pGH.kg live weight-1.d-1). All pigs had ad libitum access to their diet; pGH was administered daily from 60 to 90 kg live weight. All aspects of growth performance and body composition were affected to different degrees by gender and pGH. Strain A pigs had a higher capacity for protein accretion, superior growth performance and contained less fat in the eviscerated carcass and empty body compared with Strain B pigs. Within each strain, intact males ate more feed, had a higher rate of protein deposition and exhibited faster and leaner growth than females. Exogenous pGH administration increased average protein deposition and growth rate by 84 and 34%, respectively, and reduced average feed intake, fat deposition rate, feed:gain and carcass fat content by 14, 59, 37 and 33%, respectively. The magnitude of the changes in growth performance, tissue accretion rates and body composition elicited by pGH were independent of strain. However, within each strain the improvement in feed:gain and reduction in carcass fat measurements elicited by pGH were proportionately larger for females than for intact males.     

Effect of porcine somatotropin on number of granulosa cell luteinizing hormone/human chorionic gonadotropin receptors, oocyte viability, and concentrations of steroids and insulin-like growth factors I and II in follicular fluid of lean and obese gilts.

Prepubertal gilts of obese (n = 24) or lean (n = 24) genetic lines were injected (s.c.) daily with 0, 2, or 4 mg of porcine somatotropin (pST) for 6 wk starting at 160 d of age to determine whether pST affects follicular function. Blood and ovaries were collected at slaughter 24 h after the last injection. Surface follicles greater than or equal to 1.0 mm in diameter were counted, and pools of follicular fluid (FFL) and granulosa cells were collected from 1.0- to 3.9-mm (small) and 4.0- to 6.9-mm (medium) follicles. Oocytes were collected from small and medium follicles and evaluated for maturational stage and viability. Porcine somatotropin increased (P less than .08) the numbers of small but not the numbers of medium follicles per gilt (P greater than .10). Oocyte maturation and viability were not affected by pST or genetic line. Porcine somatotropin increased (P less than .05) concentrations of insulin-like growth factor I (IGF-I) in serum and FFL of both obese and lean gilts; IGF-I was lower (P less than .01) in lean gilts. Treatment with pST decreased (P less than .05) IGF-II in FFL of lean but not in that of obese gilts. Dose of pST and line had no effect on concentrations of progesterone in FFL of small or medium follicles or on concentrations of estradiol in FFL of small follicles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of carbohydrate source on growth performance, carcass traits, and meat quality of growing-finishing pigs

Two experiments were conducted to determine the effect of substituting a more available dietary carbohydrate (CHO) for portions of corn or fat in the diet on growth performance, carcass traits, meat quality, and serum or plasma metabolites in growing-finishing pigs. A three-phase feeding program was used with corn-soybean meal diets formulated to provide 105% of the Lys requirement for barrows or gilts gaining 325 g of lean daily in Exp. 1 or gilts gaining 350 g of lean daily in Exp. 2. Diets were isoenergetic within experiments. All other nutrients met or exceeded suggested requirements. In Exp. 1, pigs were allotted to three dietary treatments (0, 7.5, or 15.0% sucrose), with three replications of barrows and three replications of gilts, and with three or four pigs per replicate pen; average initial and final BW were 25.2 and 106.7 kg. In Exp. 2, gilts were allotted to two dietary treatments (waxy [high amylopectin] or nonwaxy [75% amylopectin and 25% amylose] corn as the grain source), with five replications of four gilts per replicate pen; average initial and final BW were 37.7 and 100.0 kg. In Exp. 1, ADG and gain:feed ratio increased linearly (P < 0.02) as dietary sucrose increased. Minolta color scores, a* and b*, and drip loss (P < 0.06) also increased linearly with added sucrose. In Exp. 2, ADG, carcass weight and length, and the Minolta a* value were greater for pigs fed waxy corn (P < 0.08) than for those fed nonwaxy corn. Feed intake, longissimus muscle area, 10th-rib and average backfat thickness, dressing percentage, fat-free lean, percentage of lean and muscling, lean gain per day, total fat, percentage fat, lean:fat ratio, serum or plasma metabolites (Exp. 1: serum urea N; Exp. 2: serum urea N, and plasma nonesterified fatty acids, triacylglycerols, total and high-density lipoprotein cholesterol, insulin, and total protein), pH of the longissimus muscle, and subjective muscle scores (color, firmness-wetness, and marbling) were not affected by diet in either experiment. In summary, increasing availability of dietary CHO in growing-finishing pig diets improved growth performance, but it did not affect carcass traits.     

Effects of exogenous porcine growth hormone administration between 30 and 60 kilograms on the subsequent and overall performance of pigs grown to 90 kilograms

Twenty-eight barrows were used to investigate the effects of exogenous porcine growth hormone (pGH) administration (0 and 100 micrograms.kg-1.d-1) between 30 and 60 kg on the subsequent and overall performance and carcass composition of pigs grown to 90 kg. The pGH was administered by daily i.m. injection and all pigs were fed one diet. Control animals were pair-fed to the intake noted for pGH-treated pigs between 30 and 60 kg and all pigs were fed ad libitum from 60 to 90 kg. Pigs administered pGH had an improved rate (36%) and efficiency (28%) of gain and an improved protein accretion rate (46%) compared to excipient-treated pigs. Pigs previously treated with pGH continued to exhibit superior (P less than .01) rate and efficiency of gain, and the gain was associated with enhanced protein accretion during the quiescent (postinjection) period compared with excipient counterparts. Administration of pGH between 30 and 60 kg reduced carcass fat and increased carcass protein and water at 90 kg, although fat accretion rate was comparable to that of control pigs. Results indicate that, to varying degrees, the stimulatory effects of pGH on growth performance are sustained following cessation of hormone treatment.     

The relationship between endogenous insulin-like growth factors and growth in pigs.

Previous studies have reported conflicting data on gender differences in plasma IGF-I in postnatal pigs. There is also debate over the role of IGF-II in regulation of postnatal growth. We have, therefore, determined the concentrations of plasma IGF-I, IGF-II, and IGF-binding protein-3 (IGFBP-3) in boars, barrows, and gilts and related these to postnatal growth characteristics. Plasma concentrations of IGF-I were higher in boars than in gilts or barrows from 13 wk. of age, and plasma IGF-II levels were generally higher in barrows than in boars or gilts. Plasma IGFBP-3 levels were higher in boars than in gilts or barrows at most ages. Between 15 and 23 wk. of age, IGF-I and IGFBP-3, but not IGF-II, were positively associated with growth rate, voluntary feed intake, and gain:feed ratio. Plasma IGF-II, but not IGF-I or IGFBP-3, was positively associated with backfat depth during this period. These results support the hypothesis that circulating IGF-I and IGF-II are regulators of lean and adipose tissue growth, respectively.     

Stimulation of swine growth by porcine growth hormone

Highly purified porcine growth hormone (pGH; USDA-B1) was administered by im injection (22 micrograms X kg body weight-1 X d-1) to rapidly growing Yorkshire barrows for 30 d. Growth hormone significantly increased growth rate (10%), feed efficiency (4%), cartilage growth and muscle mass. However, pGH did not affect carcass adipose tissue mass. Intramuscular lipid content of the longissimus was increased 50% by pGH administration. Plasma pGH concentration was elevated (7- to 11-fold) for 3 to 5 h post-injection. Chronic administration of pGH depressed pituitary GH content and concentration approximately 45%. No GH antibodies were detected in the plasma of GH-treated swine. Plasma somatomedin-C concentration was increased 55% by GH treatment 3 h post-injection. Plasma glucose and insulin concentrations were both significantly increased in GH-treated swine, suggesting that the animals had developed a state of insulin resistance. Plasma-free fatty acid concentration tended to be higher in GH-treated animals. Treatment of swine with pGH significantly decreased plasma blood urea nitrogen. Assessment of animal health during the trial and postmortem indicated that pGH administration did not have any adverse effects. In summary, treatment of young, rapidly growing swine with pGH stimulated growth performance without affecting animal health or inducing the production of GH antibodies.     

Effects of long-term administration of pituitary-derived bovine growth hormone and estradiol on growth in steers

Sixty-three Friesian steers (9 mo old, 257 kg; n = 15 or 16/treatment) were employed in a 2 x 2 factorial to test bovine growth hormone (bGH) and estradiol (Compudose implant). Steers received daily subcutaneous injections of vehicle or bGH (40 micrograms/kg body weight) for 22 wk. Steers were slaughtered 8 wk after the end of bGH treatment (wk 30). Steers had ad libitum access to silage plus a fixed amount (4 to 5.5 kg/d) of concentrate. Average daily gain (ADG) and feed conversion efficiency (FCE) improved (P less than .05) in response both to bGH and to estradiol during wk 0 to 22. Although bGH did not affect ADG or FCE during wk 23 to 30, estradiol improved (P less than .05) them; bGH and estradiol appeared additive (nonsignificant interactions) during wk 0 to 22. At slaughter, estradiol increased (P less than .05) carcass weight and carcass and leg length while decreasing (P less than .05) conformation score and percentage of kidney, knob and channel fat (KHP); bGH decreased (P less than .05) KHP. Although both bGH and estradiol increased (P less than .01) plasma GH, their effects were not additive. Both bGH and estradiol increased (P less than .01) plasma somatomedin-C and decreased (P less than .01) plasma urea nitrogen concentrations; effects were additive. Estradiol, but not bGH, increased (P less than .05) plasma glucose, whereas neither bGH nor estradiol altered plasma creatinine and nonesterified fatty acids. In summary, both bGH and estradiol improved growth and FCE, and their effects appeared to be additive. It is likely that some of their effects were mediated by somatomedin-C.     

Effects of pantothenic acid on growth performance and carcass characteristics of growing-finishing pigs fed diets with or without ractopamine hydrochloride

Two experiments evaluated effects of added pantothenic acid on performance of growing-finishing pigs. In Exp. 1, 156 pigs (PIC, initial BW = 25.7 kg) were used in a 3 x 2 x 2 factorial to evaluate the effects of added pantothenic acid (PA; 0, 22.5, or 45 ppm), ractopamine.HCl (RAC; 0 or 10 mg/kg), and sex on growth performance and carcass traits. Pigs were fed increasing PA from 25.7 to 123.6 kg (d 0 to 98) and RAC for the last 28 d before slaughter. Increasing the amount of added PA had no effect (P > 0.40) on ADG, ADFI, or G:F from d 0 to 70. A PA x sex interaction (P < 0.03) was observed for ADG and G:F from d 71 to 98. Increasing the amount of added PA increased ADG and G:F in gilts, but not in barrows. Increasing the amount of added PA had no effect (P > 0.38) on carcass traits. Added RAC increased (P < 0.01) ADG and G:F for d 71 to 98 and d 0 to 98 and increased (P < 0.01) LM area and percentage lean. In Exp. 2, 1,080 pigs (PIC, initial BW = 40.4 kg, final BW = 123.6 kg) were used to determine the effects of increasing PA on growth performance and carcass characteristics of growing-finishing pigs reared in a commercial finishing facility. Pigs were fed 0, 22.5, 45.0, or 90 mg/kg of added PA. Increasing the amount of added PA had no effect (P > 0.45) on ADG, ADFI, or G:F, and no differences were observed (P > 0.07) for carcass traits. In summary, adding dietary PA to diets during the growing-finishing phase did not provide any advantages in growth performance or carcass composition of growing-finishing pigs. Furthermore, it appears that the pantothenic acid in corn and soybean meal may be sufficient to meet the requirements of 25- to 120-kg pigs.     

The effects of ractopamine-hydrogen chloride (Optaflexx) on performance, carcass characteristics, and meat quality of finishing feedlot heifers

Two experiments were conducted at the Kansas State University Beef Cattle Research Center to determine the effects of ractopamine-HCl (Optaflexx) on growth performance, carcass characteristics, and meat quality of finishing feedlot heifers. In Exp. 1, heifers implanted with Revalor-H (n = 302, initial BW = 479 kg) were fed steam-flaked corn diets with 0 (control) or 200 mg of ractopamine-HCl (OPT) per heifer daily for 28 d before slaughter. Average daily gain and DMI were not different between treatments (P > 0.17); however, OPT cattle tended to have a greater G:F (P = 0.06). Treatments did not differ with respect to final BW, HCW, dressing percentage, USDA yield grade, USDA quality grade, marbling score, LM area, KPH, Warner-Bratzler shear force, weight loss during cooking, or L*, a*, or b* colorimetric values during a 7-d retail display or purge loss from loin steaks during retail display (P > 0.19). In Exp. 2, nonimplanted crossbred heifers (n = 281, BW = 451 +/- 2 kg) were fed finishing diets based on steam-flaked corn. A control diet (no ractopamine) was compared with diets providing 200 mg of OPT per heifer daily for periods of 28 or 42 d (200 x 28 and 200 x 42, respectively), 300 mg/d for 28 d (300 x 28), and a step-up regimen consisting of 14 d at 100 mg, followed by 14 d at 200 mg, and the final 14 d at 300 mg of OPT (step-up). Feeding OPT had no effect on carcass weight gain among treatments (P = 0.18). The efficiency of carcass gain was 34 and 35% greater (P = 0.06) for the 200 x 42 and step-up groups compared with control, respectively. Feeding OPT at 300 mg for 28 d reduced DMI compared with the control, 200 x 28, and 200 x 42 (P < 0.05) groups. Administration of OPT had no effect on marbling score, yield grade, LM area, KPH, or percentages of carcasses grading USDA Choice (P > 0.10). Feeding ractopamine-HCl (Optaflexx) to finishing heifers generally improved the efficiency of carcass gain with minimal effect on carcass characteristics. These effects were most pronounced in heifers fed ractopamine for 42 d.     

Growth and carcass characteristics and serum growth hormone, prolactin and insulin profiles in Debouillet lambs treated with ovine growth hormone and(or) zeranol

Sixteen Debouillet wether lambs (approximately 3 mo old) were placed indoors in 1.5- x 3-m pens (14 h light:10 h dark) 28 d after weaning. Lambs received no implant or a 12-mg zeranol implant on d-2 (eight lambs/group). Two days later (d 0), animals received either 0 or 2.5 mg ovine growth hormone (oGH, eight lambs/group) s.c. on alternate days for 42 d. Animals had ad libitum access to water, salt, mineral and a pelleted alfalfa diet (16% CP). After 42 d, lambs were slaughtered to evaluate carcass traits, organ weights and femur characteristics. Zeranol by oGH interactions were not detected (P greater than .20). Zeranol increased (P less than .05) BW, improved (P less than .05) feed:gain during the first 20 d and increased (P less than .10) feed intake during the last 22 d of the 42-d trial compared with controls. Carcass characteristics were not altered (P greater than .10) by 12 mg zeranol. Serum insulin and prolactin were elevated (P less than .05), but serum GH was not influenced by zeranol compared with controls. Exogenous oGH decreased feed intake (P less than .10) and improved feed:gain (P less than .05) during the initial 20 d compared with controls, but did not influence (P greater than .20) these variables during the last 22 d of the study. Carcass traits were not influenced (P greater than .10) by oGH. Exogenous ovine GH dramatically elevated (P less than .05) serum GH, but did not affect serum insulin or prolactin (P greater than .10).(ABSTRACT TRUNCATED AT 250 WORDS)     

Interestrous interval of cyclic gilts is decreased by systemic but not intrauterine administration of exogenous oxytocin

Oxytocin (OT) stimulates pulsatile secretion of uterine prostaglandinF2alpha in ruminants, but the role of OT in the estrous cycle regulation of pigs is not clear. These studies were performed to determine the effect of exogenous OT on interestrous interval of intact cyclic gilts. Intrauterine infusion of 80 USP units three times daily on d 10 to 16 after estrus did not decrease interestrous interval (24.5+/-1.3 d) compared with control gilts (22.5+/-1.3 d). In contrast, i.m. injections of 20 USP units of OT twice daily or 80 USP units of OT three times daily on d 10 to 16 after estrus decreased (P < 0.05) interestrous interval (20.0+/-0.3 or 19.5+/-0.4 d, respectively) compared with control gilts (20.5+/-0.3 d). When gilts received a single i.m. injection of 0 or 1 mg of estradiol valerate on d 11 and twice daily i.m. injections of 0 or 20 USP units OT on d 10 to 16 after estrus, an interaction (P = 0.05) between OT and estradiol valerate was detected. In the absence of exogenous estradiol valerate, injection of OT decreased interestrous interval (19.0+/-0.5 d) compared with injection of vehicle (20.4+/-0.5 d). However, when gilts were injected with 1 mg of estradiol valerate to inhibit luteolysis, OT did not prevent the increase in interestrous interval (25.4+/-0.5 d) compared with injections of vehicle (24.7+/-0.5 d). These results indicate that 1) exogenous OT administered by intrauterine infusion on d 10 to 16 did not decrease interestrous interval of intact cyclic gilts, 2) exogenous OT administered i.m. on d 10 to 16 shortened interestrous interval, and 3) exogenous OT did not prevent the increase in interestrous interval induced by estradiol valerate.     

Growth, carcass and palatability traits of intact males and steers implanted with zeranol or estradiol early and throughout life

This study was conducted to assess the impact of implanting intact beef males with protein anabolic agents at varying intervals throughout life. Ninety-six intact males were assigned to three implant treatments: 1) not implanted, 2) implanted at 9 wk of age, weaning and at 56-d intervals thereafter with a 36-mg zeranol implant or 3) estradiol implant at 9 wk of age and 68 d post-weaning. During the 118-d, post-weaning growing period, eight animals per treatment (one replication) were castrated. After a 114-d finishing period, cattle were slaughtered (average age of 13 to 14 mo). Feedlot performance, carcass and palatability data were obtained. Average daily gains and feed efficiency did not differ (P greater than .05) between zeranol and estradiol-implanted intact males. Regardless of implant treatment, steers had lighter carcass weights (P less than .05) and higher (P less than .01) quality grades than intact males. Implanting either intact males or steers with zeranol or estradiol resulted in higher (P less than .05) numerical yield grades. Quality grades were higher in zeranol-implanted cattle than the non-implanted or estradiol-implanted cattle. Intact males implanted with zeranol were similar in carcass fatness to zeranol-implanted steers. No differences (P greater than .05) in tenderness or connective tissue were detected. Implanting intact males early and throughout life with zeranol made them similar to steers in fatness, while estradiol implantation had few effects on carcass and palatability traits of intact males or steers.     

Stimulation of pig growth performance by porcine growth hormone: determination of the dose-response relationship

The present study was undertaken to determine the relationship between dose of porcine growth hormone (pGH) and growth performance of pigs. Porcine GH was administered daily for 35 d [buffer-injected control = (C); 10 micrograms/kg body weight (BW) = (L); 30 micrograms/kg BW = (M); 70 micrograms/kg BW = (H)] to barrows (initial wt = 50 kg). Growth rate was significantly increased by pGH (14% for H dose vs C). Feed efficiency was increased in a dose-related manner (L = 7%, M = 10%, H = 17%) by pGH. There was a concurrent change in carcass composition of pGH-treated pigs. The H dose of pGH decreased the percentage of carcass lipid by 25% (P less than .05). Muscle mass was significantly increased in H vs C pigs (31 vs 26 kg). Serum insulin-like growth factor 1 (IGF-1) concentration increased in a manner that was linearly related to the pGH dose (r = .87). No antibodies to pGH were detected in any of the pigs. In summary, these results extend our earlier findings that pGH increases growth performance markedly. Based on the present findings it appears that the maximally effective dose of pGH is greater than 70 micrograms.kg BW-1.d-1 since several indices of the growth-promoting and metabolic effects of pGH (% carcass protein, % carcass lipid and feed efficiency) had not plateaued.