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-mu-g/kg of BW, with dose adjusted every 5th d for changes in BW (A; adjusted), or 70-mu-g/kg of initial BW (U; unadjusted). Gilts were slaughtered on d 25. Gilts treated with pGH had higher ADG (P < .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 < .01) for Groups A and U than for Group C gilts. Average backfat thickness was less (P < .004) for A and U gilts than for C gilts and less for Group A than for Group U (P < .02). Furthermore, growth and carcass traits were similar (P > .05) for Groups A and U, except for measurements of first rib backfat, last rib backfat, and average backfat depth (P < .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 < .05). Addition of LH to the culture media enhanced secretion of P4 by cultured GC from pGH-treated gilts only (P < .05). Production of insulin-like growth factor I (IGF-I) by GC was not different among in vivo treatment groups (P > .05) in unsupplemented cultures on d 3 and 7; however, supplementation with either epidermal growth factor or FSH tended to increase production of IGF-I by GC from pGH-treated gilts. Therefore, we conclude that daily administration of a constant dose of pGH results in growth and efficiency responses similar to those achieved with periodic adjustment of dose for increasing BW. These results contrast with our previous report that exogenous pGH administered to prepubertal gilts decreases steroidogenic capacity of GC in vitro. Considering the substantial savings in pGH realized over a 24-d period, administration of a constant mass of pGH to gilts seems to be a viable alternative to adjusting the dosage of pGH for changes in BW.