Roy N. Kirkwood

The influence of growth hormone injections on the endocrine and metabolic status of gilts

Twelve Yorkshire x Landrace prepubertal gilts were assigned equally to treatments involving daily injections of either porcine growth hormone (GH, 90 micrograms/kg) or vehicle buffer from 150 to 159 d of age. Blood samples were obtained every hour from 0600 hr at 153 d until 0500 hr at 154 d of age, inclusively. At 0800 hr on 154 d, gilts received an injection of 500 IU PMSG, followed 96 hr later by 250 IU hCG. Gilts were slaughtered at 163 d and the ovaries recovered for an assessment of the ovarian response to the gonadotrophic stimulation. Five control gilts (83%) exhibited a normal ovulatory response but only one GH gilt (17%) was so designated (P less than 0.05). There was no apparent effect of treatment on serum concentrations of LH, FSH or cortisol. Growth hormone treatment reduced serum concentrations of T4 (P less than 0.001) and prolactin (P less than 0.02), but increased serum GH (P less than 0.001), T3 (P less than 0.06), insulin (P less than 0.001) and glucose (P less than 0.001). Serum concentrations of free fatty acids (FFA) were not significantly altered by exogenous GH. The concomitant elevation of serum insulin and glucose suggests that an insulin-resistant state was induced which, if evident at the ovarian level, may be a factor mediating the adverse effects of exogenous GH on ovarian function. The data presented also suggests that circulating concentrations of thyroid originating hormones are altered by exogenous GH.

Management of Replacement Breeding Animals

In conclusion, replacement gilts should be finally selected before 110 kg body weight and should have been stimulated to reach puberty by this time. Currently, the best method for achieving this is ad libitum feeding and the correct use of boar exposure. However, whether ad libitum feeding will always be the best feeding strategy remains to be seen. The impressive success of selection programs and the potential for the use of growth promoters and repartitioning agents in the feeder barn may require that future replacements be identified at an early stage and raised under a separate feeding regimen. To produce a large first litter, gilts should be bred at their second estrus. There is unlikely to be any further increase in litter size by delaying mating to third estrus. A major consideration when choosing when to breed replacements is the length of their productive life. For many farms, this may be maximized by delaying breeding until the sow is 120 to 130 kg body weight with a minimum backfat depth of 18 mm. For the producer who is able to exert control over lactation condition loss, however, breeding replacements at about 110 kg body weight with backfat depths of 14 to 16 mm should not adversely affect long-term performance. Although it is true that, under some conditions, the lean gilt may become a problem, it is equally true that her potential is as great as her fatter contemporaries. Whether this potential is realized is largely under the producers control. Regarding the boar, nutritional management need not vary from that provided for gilts. However, if replacement boars are raised on-farm, it is of great importance that they be allowed to socially interact with other pigs. Failure to provide this opportunity will result in a boar with reduced libido.

The influence of exogenous pituitary growth hormone on the ovulatory response to PMSG and hCG and the LH response to estradiol benzoate in prepubertal gilts

Two experiments were performed to examine the influence of exogenous growth hormone on the reproductive axis in gilts. Experiment one employed 26 Yorkshire X Landrace prepubertal gilts, which were selected at 150 d and 86.5 +/- 1.5 kg bodyweight (BW) and assigned equally to two treatments. Gilts received injections of either porcine growth hormone at 90 micrograms/kg BW, or vehicle buffer, from 150 to 159 d. At 154 d gilts received 500 IU PMSG, followed 96 hr later by 250 IU hCG. Gilts were slaughtered at 163 days and their ovaries recovered to determine ovulatory status. In each treatment, 2/13 gilts failed to show any ovarian response to PMSG/hCG. All remaining control gilts ovulated and their ovaries appeared morphologically normal. In gilts receiving exogenous growth hormone, fewer ovaries (4/11, P less than .01) appeared morphologically normal. The ovaries of all other growth hormone injected gilts had very large (12-25 mm) non-luteinized follicles. In experiment two, 20 prepubertal Yorkshire X Landrace gilts were selected at 138 days and 85 kg BW. These gilts received injections of growth hormone at 90 micrograms/kg BW (n = 9) or vehicle (n = 11) from 138 to 147 days. At 143 days, all gilts were given an injection of estradiol benzoate (EB) at 15 micrograms/kg BW. Blood samples were taken at the time of EB injection, at 24 and 36 hr and then at 6 hr intervals until 78 hr. All samples were assayed for serum LH concentrations. The EB induced LH peak height was lower (P less than .04) in gilts receiving exogenous growth hormone than in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Observations on the influence of active immunization against somatostatin on the reproductive performance of sheep and pigs.

Somatostatin (SRIF) is known to have inhibitory effects in a wide variety of tissues but a role in reproduction has not been described. The present studies describe the influence of SRIF immuno-neutralization on the reproductive performance of sheep and pigs. In experiment 1, Rambouillet x Suffolk ewe lambs were actively immunized against SRIF conjugated to ovalbumin (SI; n = 24) or were not immunized (CT; n = 32). Primary immunizations were initiated at weaning and boosters given at 4-week intervals, as well 10 days before breeding and lambing. Over two years, breeding periods were September and January (in-season) and May (out-of-season). Pregnancy rates were higher for SI than for CT ewes following both in-season (P less than 0.01) and out-of season breeding (P less than 0.06). The number of lambs born per ewe lambing was not affected by treatment. In experiment 2, Yorkshire x Landrace gilts were actively immunized against SRIF-ovalbumin conjugate (n = 37) or were not immunized (n = 38). Primary immunizations were given at 39.8 +/- 1.5 kg body weight and boosters after 4 weeks, 10 days before breeding and at 105 days of gestation. Some SI (n = 15) and CT gilts (n = 17) were slaughtered 10 days after estrus to determine ovulation rates. Remaining SI (n = 22) and CT (n = 21) gilts carried their litters to term. Ovulation rates tended to be higher (P less than 0.1) in SI than CT gilts (11.8 +/- 0.6 vs. 10.7 +/- 0.4). There was no effect of treatment on pregnancy rates to initial breeding (86.4 vs. 90.5% for SI and CT gilts, respectively) but first litter size tended to be larger (P less than 0.07) for SI than for CT gilts (9.95 +/- 0.34 vs. 9.00 +/- 0.38). There was no effect of treatment on litter growth performance during lactation. These data provide evidence that SRIF may be involved in the regulation of reproduction.

The effect of exogenous insulin-like growth factor-I (IGF-I) on the reproductive performance of female rats, and on serum concentrations of endogenous IGF-I and IGF-I binding proteins☆

The effect of exogenous IGF-I on the reproductive performance of female rats was examined by infusing either recombinant human IGF-I (400 micrograms/d; n = 19) or vehicle (n = 18) over a four-day period (the time of one reproductive cycle) beginning on the day following estrus. The females were exposed to male rats one day after the infusions had commenced, and were euthanized 15 d later. There was no treatment effect on serum progesterone levels at this time or on the number of fetuses. Furthermore, the number of corpora lutea were not different between the IGF-I and vehicle infused groups (15.8 vs. 14.8; P = 0.09). Total serum IGF-I concentrations, as determined with a polyclonal antiserum based RIA, were increased approximately three-fold in samples obtained 20 hr after commencing the IGF-I infusion. These samples were also analyzed for IGF-I with a monoclonal antibody based RIA previously shown to detect human, but not rat, IGF-I. By subtraction, the concentration of endogenous rat IGF-I was found to be approximately 60% higher in IGF-I-infused rats than in control rats. This increase was likely due to a reduced clearance rate of IGF-I from the circulation, caused by a marked induction of 42-46 kDa and 30-34 kDa IGF-I binding proteins observed in these samples with a ligand blot technique. The binding protein induction indicates that the infused IGF-I was bioactive. This induction may have attenuated the effects of IGF-I on ovarian function.