Effects of treatment with LH and FSH between 8 and 12 weeks of age on ovarian follicular development and puberty in heifers

The transient increase in gonadotrophin secretion, seen in heifer calves between 6 and 20 wk of age, may be critical for early ovarian follicular growth and for initiation of sexual maturation. We treated heifers with either 3 mg of bLH (n = 5; sc) or 4 mg sc of bFSH (n = 5; sc), every other day, between 8 and 12 wk of age. During the first 17 d of treatment, bovine gonadotrophins caused a reduction in maximum antral follicle size and in numbers of large antral follicles, compared to control heifers (P < 0.05). In 4 of 5 bLH treated heifers and 3 of 5 bFSH treated heifers, the emergence of a large dominant antral follicle was delayed (P < 0.05). At 34 wk of age, follicular dynamics did not differ among groups. Serum concentrations of estradiol were decreased in bFSH and bLH treated heifers at 35 wk of age and in bFSH treated heifers at 25 wk of age compared with that of the controls. Time of first ovulation was delayed in bFSH treated heifers compared with control heifers (P < 0.05;bFSH 59.0 +/- 1.2; control 51.4 +/- 1.8; bLH 56.2 +/- 2.5 wk of age). In summary, treatment of 8-wk old heifers with gonadotrophins every other day disrupted folliculogenesis over a 17-d period, delayed first ovulation (bFSH), and decreased ovarian estradiol production at 25 (bFSH) and 35 (bLH, bFSH) weeks of age.