THE INFLUENCE OF GROWTH-HORMONE INJECTIONS EITHER PRE-BREEDING OR POSTBREEDING ON THE REPRODUCTIVE-PERFORMANCE OF SOWS AND GILTS

Two experiments were conducted to examine the effect of porcine growth hormone (pGH) injections on reproductive performance of swine. In exp . 1, 62 mixed-parity Yorkshire x Landrace sows received 6 mg of pGH ei ther daily (n = 20) or on alternate days (n = 20) from 2 d preweaning until 4 d postweaning, with remaining sows (n = 22) serving as control s. A single blood sample was obtained from each sow prior to the first injection, at weaning and at 4 d postweaning and samples were assayed for insulin, IGF-I and triiodothyronine (T3). Serum insulin tended (P = 0.1) to be higher at 4 d postweaning in sows injected daily but was unaffected by injections on alternate days. However, T3 and IGF-I wer e higher (P < 0.05 and P < 0.01, respectively) in both pGH groups comp ared with controls. No significant effects of either pGH treatment wer e apparent for the mean remating interval or subsequent litter size bu t the rebreeding interval was less variable (P < 0.01) for sows inject ed on alternate days. In experiment two, 40 Yorkshire x Landrace gilts received either 6 mg of pGH or vehicle on alternate days from days 5 to 21 of pregnancy. Single blood samples were obtained on days 5, 10, 15 and 20 of pregnancy and were assayed for insulin, IGF-I, T3 and pro gesterone. The injection of pGH had no effect on serum insulin or prog esterone, caused a mild increase (P = 0.15) in serum T3 and increased (P < 0.01) serum IGF-I. There was no effect of treatment on pregnancy rate, ovulation rate, number of embryos or on embryo weight or crown-r ump length. From the data of both experiments, we conclude that the in jection of pGH either pre- or post-breeding will not improve the repro ductive performance of swine.