Ontogeny of ovarian follicle development in Booroola sheep fetuses that are homozygous carriers or non-carriers of the FecB gene.

The aims of this study were to examine the effects of the Booroola FecB gene on ovarian development and reproductive hormones (FSH, LH and inhibin) at days 90, 100, 120 and 135 of gestation (term = 147 days). The effects of litter size were eliminated by transferring equal numbers of homozygous BB and control (++) embryos to recipient ewes. The ovary, but not the body, pituitary, adrenal, kidney or thymus, was heavier (P < 0.05) in BB compared with ++ fetuses at day 90 but not thereafter. In the ovary, gene-specific differences were observed in the total number of germ cells present at days 90 (P < 0.01) and 135 (P < 0.05) with the same tendency being noted at day 100 (P < 0.07); at all of these ages the mean numbers of germ cells in the BB genotype exceeded those in ++ animals. Gene-specific differences were observed in the numbers of oogonia and isolated oocytes at day 90 (i.e. BB > ++), in the number of primordial follicles at days 100 (BB > ++) and 135 (BB > ++), and also in the number of primary or secondary follicles (++ > BB) at day 135. At each gestational age examined no differences were noted with respect to the plasma concentrations of FSH, LH or inhibin between the BB and ++ fetuses. However, the highest mean plasma concentrations of FSH and LH occurred at days 90 and 100 of gestation, which coincided with the first developing primary follicles.(ABSTRACT TRUNCATED AT 250 WORDS)