Ovarian characteristics in sheep with multiple fecundity genes

Ewes heterozygous for combinations of the Inverdale (FecXI; I+), Booroola (FecB; B+) and Woodlands (FecX2W; W+) mutations have ovulation rates higher than each mutation separately. The aims of the experiments described herein were to examine the ovarian phenotypes in I+B+ and I+B+W+ ewes and to compare these with the appropriate ++ controls and with I+ and BB animals available for this study. The mean±S.E.M ovulation rates in the ++ (n=23), I+ (10), I+B+ (7), I+B+W+ (10) and BB (3) animals were 1.8±0.1, 2.5±0.2, 6.6±1.0, 9.6±0.9 and 9.7±0.9 respectively. The maximum number of granulosa cells per follicle in the ++ and I+ genotypes was accumulated after exceeding 5mm diameter whereas in I+B+, I+B+W+ and BB animals, this was achieved when follicles reached 2-<3 mm. The number of putative preovulatory follicles, as assessed from those with LH-responsive granulosa cells, 24h after the induction of luteolysis, was higher (P<0.01) in the I+B+ and I+B+W+ compared to the ++ and I+ genotypes. The median follicular diameters of these follicles in the ++, I+, I+B+, I+B+W+ and BB genotypes were 6, 5 3, 3, and 3 mm respectively. The total number of granulosa cells accumulated in the putative preovulatory follicles did not differ between the genotypes. Likewise, no differences were noted in the total mass of luteal tissue indicating that the higher the ovulation rate, the smaller the individual corpora lutea. The ovarian characteristics following ovulation in all of these mutations alone or in combination differs from that achieved following superovulation after exogenous gonadotrophin treatments.