Ovarian follicular activity in Booroola lambs with and without a fecundity gene

Abstract

The ovaries of 3-month-old Booroola lambs which were heterozygous carriers of a major gene (F) influencing the ovulation rate in mature ewes (i.e. F+ lambs) were compared to those of similarly-aged Booroola lambs which were non-carriers of the F-gene (i.e. ++ lambs). The ovaries of the F+ Booroola lambs were significantly lighter (P < 0.01) than those of ++ lambs even though the mean ± s.e.m. number of follicles (≥ 1 mm diam.) in the F+ lambs was greater than that in the ++ lambs (i.e. F+ lambs, 30.2 ± 2.5 follicles; ++ lambs, 18.4 ± 1.2 follicles; P < 0.01). In granulosa cells from non-atretic follicles (≥ 1 mm diam.) from F+ and ++ Booroola lambs, FSH (NIAMDD-FSH-S16) doses of 100 and 1000 ng/ml caused significant stepwise increases (P < 0.05) in cyclic adenosine 3',5'-monophosphate (cAMP) production compared to that achieved at FSH doses of 0 and 1 ng/ml or at any FSH dose in cells from atretic follicles. However, no significant differences in FSH-induced cAMP production were noted with regard to Booroola genotype or follicular diameter. None of the granulosa cell preparations from non-atretic follicles of 1-2.5 mm diameter from F+ lambs (N = 13) or from non-atretic follicles of 1-4.5 mm diameter from ++ lambs (N = 16) responded to LH (NIAMDD-LH-S24; 10 or 1000 ng/ml) to produce significantly more cAMP than did the controls. In contrast, the granulosa cell preparations from non-atretic follicles of 3-4.5 mm diameter from F+ lambs (N = 4) and from non-atretic follicles of ≥5 mm diameter of ++ lambs (N = 4) produced significantly more cAMP (P < 0.05) in response to LH (1000 and/or 10 ng/ml) relative to that in the controls. The theca interna from follicles of lambs of both genotypes had functional LH receptors as judged by the androstenedione responses to exogenous LH although no genotypic differences were noted. In F+ lambs, the follicular fluid concentrations of testosterone but not oestradiol (i.e. in 1-4.5 mm diam. follicles) and granulosa cell aromatase activity (i.e. in 3-3.5 mm diam. follicles) were significantly higher (both P < 0.05) than in corresponding follicles or cells from ++ lambs. Collectively the results suggest that the Booroola F-gene influences the composition and function of sheep ovaries before puberty.