Hormonal and follicular relationships in ewes of high and low ovulation rates

Abstract

Total follicular populations and peripheral plasma concentrations of LH [lutropin], FSH [follitropin], prolactin, estradiol-17.beta. and progesterone during the preceding cycle were studied in 2 breeds of sheep (Romanov and Ile-de-France) which differed widely in their ovulation rates (3.2 and 1.5, respectively). No LH parameters could be correlated with the follicular details measured. The 2nd peak of FSH occurring 20-30 h after the preovulatory LH surge was significantly larger in the Romanov ewes and the area under this peak was correlated (P < 0.01) with the number of antral follicles present in the ovary 17 days later. Formation of the antrum during the follicular growth phase apparently is under the control of FSH. The discharge of prolactin preceding the LH peak, although not significantly different between breeds, was correlated with several of the follicular classes measured, including the number of preantral follicles. The peak value of estradiol-17.beta. measured before the LH peak was significantly higher (P < 0.05) in estradiol-17.beta. measured before the LH peak was significantly higher (P < 0.04) in the Romanov ewes and was correlated with the number of the largest follicles present. There was no significant difference between breeds in the concentration of estradiol at the onset of estrus. The progesterone conentration during the luteal phase was highly correlated with the number of preovulatory follicles.