Ovarian follicle populations and ovulation rates of Finnish Landrace cross ewes in different nutritional states and associated profiles of gonadotrophins, inhibin, growth hormone(GH) and insulin-like growth factor-I

Abstract

Effects of ewe body condition and level of feed intake on ovarian follicle populations and ovulation rates were studied in three groups of 12 to 15 Finnish Landrace cross ewes. Ewes were fed to achieve target body condition scores of either 2.0 (low, LM) or 2.5 (moderate, MM) and then fed a complete pelleted ration for three weeks before study so that they maintained liveweight. Ewes of a third group were also fed to achieve condition scores of 2.5 and then fed ad libitum (MAL). Neither ewe body condition nor level of feed intake significantly affected either the number of large follicles (≥ 4 mm diameter) or the ovulation rate. The proportion of estrogenic follicles was lower in MM than LM ewes (0.77 vs. 0.96; P < 0.05), but there was no difference in this proportion between MAL and MM ewes. Insulin-like growth factor-I (IGF-I) concentrations in the follicular fluid were unaffected by ewe body condition or level of feed intake despite significant treatment differences in circulating concentrations. Inhibin concentrations were higher in estrogenic follicles of LM compared with MM ewes, and this difference was reflected in circulating profiles. Treatment differences in LH profiles were not associated with any difference in follicle populations or ovulation rate. There were no consistent treatment effects on FSH concentrations. It is concluded that the roles of inhibin and IGF-I in the control of follicle development cannot be adequately assessed on the basis of circulating concentrations alone and that there is a need to measure intrafollicular hormone profiles and associated effects on follicle physiology.