ONTOGENY OF OVARIAN FOLLICLE DEVELOPMENT IN BOOROOLA SHEEP FETUSES THAT ARE HOMOZYGOUS CARRIERS OR NONCARRIERS OF THE FEC(B) GENE

The aims of this study were to examine the effects of the Booroola Fec (B) 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 numb ers of homozygous BB and control (++) embryos to recipient ewes. The o vary, but not the body, pituitary, adrenal, kidney or thymus, was heav ier (P< 0.05) in BB compared with ++ fetuses at day 90 but not thereaf ter 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 t hese ages the mean numbers of germ cells in the BB genotype exceeded t hose in ++ animals. Gene-specific differences were observed in the num bers 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) a t day 135. At each gestational age examined no differences were noted with respect to the plasma concentrations of FSH, LH or inhibin betwee n the BB and ++ fetuses. However, the highest mean plasma concentratio ns of FSH and LH occurred at days 90 and 100 of gestation, which coinc ided with the first developing primary follicles. Collectively, the re sults from this and previous studies show that the different effects o f the Fec(B) gene in germ cell development in early gestation continue throughout fetal development independently of litter size. Moreover, during the growth of the first primary and secondary follicles at days 100 and 120, respectively, there are no differences in the plasma con centrations of FSH, LH and inhibin with respect to Booroola genotype.