Endocrine response to superovulatory treatment in pre-pubertal beef heifers: Its lack of ability to induce puberty

This study was carried out to investigate: (1) changes in plasma oestradiol-17β and progesterone concentrations in six pre-pubertal beef heifers, 9 months old, subjected to a superovulatory treatment, consisting of a single dose of PMSG followed 120 h later by a single injection of human chorionic gonadotrophin (HCG); and (2) the ability of this treatment to trigger cyclic gonadal activity. After PMSG administration, oestradiol-17β levels increased from 11·8 (s.d. 10·78) to 92·9 (s.d. 38·15) ng/1 just before HCG injection. The oestradiol-17β increase during the superovulatory treatment and numbe r of ovulations were correlated (r = 0·83; P < 0·05). After HCG injection, progesterone concentrations rose significantly reaching values which in some cases were higher than 60 [μg/1. The progesterone peak on days 9 and 10 post HCG was strongly correlated with the number of corpora lutea (r = 0·95; P < 0·01 and r = 0·92; P < 0·01, respectively). Progesterone determinations were performed for a period of 90 days after HCG administration. No evidence was found for the induction of permanent cyclic ovarian activity since all heifers returned, after the induced luteal phase, to their pre-pubertal condition.