RECOMBINANT PORCINE SOMATOTROPIN EFFECTS ON SEXUAL DEVELOPMENT AND METABOLIC STATUS OF GILTS

Prepubertal Yorkshire gilts (61.7 +/- SD 3.7 kg) served as untreated c ontrols (n = 8), were injected daily (at 15:00) for 28 d with 2 mg of porcine somatotropin (pST; n = 8), or were implanted with a prolonged- release (2 mg d-1 for 28 d) pST implant (n = 7). Gilts had ad libitum access to feed except during an overnight fast before blood sampling ( 06:00 to 22:00 h) on day 23 or 24. Feeding on day 23 or 24 resumed at 09:00 h and injected gilts received pST at 15:05 h. Gilts were slaught ered on day 28. Endogenous episodic ST secretion in both injected and implanted gilts was suppressed, but basal plasma ST in implanted gilts was elevated. Plasma insulin was elevated in response to pST injectio n and in implanted gilts postprandially, compared with controls. Plasm a insulin-like growth factor I (IGF-I) was elevated in both injected a nd implanted gilts preprandially and postinjection. Plasma nonesterifi ed fatty acids and creatinine were similar among groups. Urea nitrogen declined after feeding, and this decline was greater in injected than in implanted or control gilts. Basal episodic luteinizing-hormone (LH ) secretion, reproductive-tract weight, follicular volume, and plasma and follicular-fluid fluid estradiol-17beta were similar among groups. However, follicular-fluid IGF-I concentrations were greater in inject ed and implanted, than control gilts. We conclude that pST administrat ion (2 mg d-1) for 28 d significantly affected the ST-insulin-IGF-1 ax is, but it did not affect LH secretion or reproductive-tract developme nt. The pST-induced increase in follicular-fluid IGF-I may be of physi ological significance to continued follicular development.