PLASMA GONADOTROPIN CONCENTRATIONS AND OVARIAN CHARACTERISTICS IN INVERDALE EWES THAT ARE HETEROZYGOUS FOR A MAJOR GENE (FECX(1)) ON THE X-CHROMOSOME THAT INFLUENCES OVULATION RATE

Ewes heterozygous (I+) for the Inverdale prolificacy gene (FecX(I)) located on the X chromosome have ovulation rates approximately 1.0 times higher than noncarriers (++). The aims of this study were to examine, in I+ and ++ ewes, the peripheral plasma concentrations and/or ovarian secretion rates of FSH, LH, inhibin, estradiol, and progesterone during anestrus and the estrous cycle and after ovariectomy. Also examined were aspects of ovarian morphology and functions of granulosa cells in vitro. No FecX(I)-specific differences were noted for the ovarian hormones or for FSH or LH. However, I+ animals contained significantly more ovarian antral follicles (p < 0.05) and their granulosa cells had a higher mean LH responsiveness in vitro with respect to cAMP synthesis at smaller follicular diameters relative to ++ ewes (I+ = > 2.5 mm; ++ = > 4.5 mm). Moreover, nonatretic follicles in I+ animals compared to the ++ genotype contained fewer granulosa cells and smaller CL. Although the I+ animals had a higher ovulation rate than the controls (p < 0.05), the total weight of CL was not different between the genotypes. These findings suggest that the FecX(I) gene affects ovarian function without altering ovarian hormone secretion. The findings also suggest that there are no FecX(I)-specific differences in the mean concentrations of gonadotropins, although further studies on temporal changes in gonadotropin secretion arc warranted.