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.