The results of previous experiments indicate that the effect of body condition (BC) on ovulation rate is mediated through changes in the number of large, potentially ovulatory, ovarian follicles. However, these differences in follicle populations were not associated with consistent differences in gonadotrophin profiles. It was therefore postulated that effects of level of BC on follicle development and ovulation rate are due to differential ovarian sensitivity of FSH.

Two groups of 20 Scottish Blackface ewes were fed differentially so that they achieved mean (±s.e.m.) body condition scores of 1.78±0.017 (Low; L) and 2.94±0.031 (High; H) by 2 weeks before sample collection. They were then fed to maintain these body conditions throughout the remainder of the experiment. Four weeks before study, Alzet minipumps (Charles Rivers UK Ltd.) containing GnRH agonist (buserilin; Hoechst AG; Frankfurt, F.R.G.) were inserted, subcutaneously, in all ewes. This treatment partially suppresses FSH secretion and totally inhibits LH pulses so that growth of ovarian follicles >2.5 mm in diameter is inhibited.