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 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. Collectively, the results from this and previous studies show that the different effects of 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 concentrations of FSH, LH and inhibin with respect to Booroola genotype.

In female fetuses the Booroola gene (FecB^B) is known to affect germ cell development and consequently the pattern of ovarian follicular growth during fetal and post-natal life. However in males, the role of this gene during fetal development is unknown. The aims of the study reported here were to examine the effects of the FecB^B gene on development of male fetuses with respect to body and organ mass (for example, pituitary gland, adrenal and mesonephros), testes development, including numbers of germ cells, and also the plasma concentrations or tissue contents of the reproductive hormones (FSH, LH and testosterone) at days 40, 55, 75, 90 and 135 of gestation. The FecB^B gene was found to influence litter size, bodymass, crown–rump length and testis mass at most stages of gestation. Some effects were also noted on the mesonephros at days 40 and 55 and on the pituitary and adrenal at days 90 or 135 of gestation. However, the FecB^B gene was not observed to have an effect on the patterns of germ cell development, on pituitary content or plasma concentrations of immunoreactive or bioactive FSH or immunoreactive LH or testicular content of testosterone. When embryo transfer experiments were performed to eliminate the effects of litter size at days 40, 90 and 135 of gestation nearly all of the differences in bodymass, crown–rump length and organ mass disappeared. The only exception to this was at day 90 when bodymass continued to be lighter and crown–rump lengths smaller in the BB/B + fetuses compared with the ++ fetuses; the significance of this finding remains unknown. It is concluded that for Booroola male fetuses there are no direct effects of the FecB^B gene on pituitary gonadotrophin function or testicular development after sexual differentiation. Moreover, although there may be temporal differences around day 90 of gestation, there are no long-term, direct effects of the FecB^B gene on total body, adrenal, testis or pituitary mass. Collectively these findings for the male are similar to those for female fetuses except with regard to germ cell development.