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Reproductive and Growth Responses of Gilts to Exogenous Porcine Pituitary Growth Hormone^1,2,

The Pennsylvania State University, University Park 16802 and Hershey 17033

Abstract

Forty gilts (mean wt = 72 kg) were administered daily either vehicle (C = control) or 70 Hg 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 3 5 additional days and examined twice daily for estrus. Estrual 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 > .1) or Exp. 2 (P = .09). Uterine weights were greater for pGH-treated than for C gilts (P < .007) in Exp. 1, but not in Exp. 2. Concentrations of estradiol (E₂) in plasma and FFl and of progesterone (P) in plasma and FFl were not different for pGH and C gilts. Concentrations of insulin-like growth factor-I (IGF-I) in FFl and in serum were greater for pGH than for C gilts (P < .01). Concentration of P in serum-free medium of cultured GC was lower for GH than for C (P < .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 < .025). In Exp. 1, ADG was higher (P < .03) and feed/gain lower (P < .07) for pGH gilts. Longissimus muscle area (LMA) was not different (P = .19) between groups. Backfat thickness (BF) was lower (P < .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.

¹ Paper no. 7888 in the Journal Series of the Pennsylvania Agric. Exp. Sta. Portions of this material were presented at the 79th Annu. Mtg. of ASAS, Logan, UT.

² Appreciation is expressed to D. J. Bolt for porcine growth hormone, to V. E. Hazlett and D.J.E. Hosterman for care of animals and to J. Watkins, J. Smeal, D. Butts and R. Robinson for assistance in slaughter of animals.

³ Dept. of Dairy and Anim. Sci.

⁴ Dept of Med., Hershey Medical Center.

⁵ Reprint requests: Dr. D. R. Hagen, 304 Henning Bldg., University Park, PA 16802.