Summary. The tissue contents of adenosine cyclic 3′,5′-monophosphate (cAMP) in freshly dissected follicles (0·13–1·00 mm diam.) were significantly higher in Booroola ewes containing a major fecundity gene (FF and F+ ewes) compared to those values in Booroolas with no copy of the gene ( + + animals; P < 0·025). After a 1 h incubation with LH + FSH, the respective proportions of follicles with a diameter of 0·13–0·52 mm (n = 288) and 0·53–1·00 mm (n = 271) that had synthesized ≥0·6 pmol cAMP and ≥1·0 pmol cAMP were significantly influenced by genotype (Booroola ewes homozygous for the F-gene, FF > heterozygous, F+ > ++; P <0·01 for both follicle size ranges).
The contents of progesterone, androstenedione, testosterone and oestradiol-17β in minced ethanolic extracts of freshly dissected follicles (n = 188) were undetectable regardless of Booroola genotype. However, when follicles of 0·53–1·00 mm but not 0·13–0·52 mm diameter were cultured for 48 h with LH + FSH under 70 kPa of a 50% O2, 45% N2 and 5% CO2 gas mixture, the proportions that synthesized high levels of progesterone (≥4·0 ng), androstenedione (≥3 ng), and oestradiol (≥0·8 ng) were significantly influenced by genotype (FF > F+ ≥ ++; P <0·05 for each steroid). No significant genotypic differences were noted for testosterone synthesis.
Collectively, these results show that the Booroola F-gene has an influence on the maturation of ovarian follicles from an early stage of growth.