Prenatal androgens modify the reproductive response to photoperiod in the developing sheep.

In most seasonal breeders, photoperiod influences the timing of the transition to sexual maturity. In sheep, males and females express reproductive maturity under different photoperiods. Spring-born males begin the maturational process during lengthening days (spring), whereas females do so during shortening days (autumn). We hypothesized that photoperiod differentially influences the transition to sexual maturity in each sex, and that this difference results from the presence or absence of androgens prenatally. The monitored the timing of sexual maturity in male and female lambs (n=8 each) and in prenatally masculinized female lambs (n=7) maintained under controlled photoperiods (natural-simulate or reverse natural-simulate). Circulating LH was analyzed to reveal the timing of the pubertal gonadotropin rise; lambs were gonadectomized and implanted with estradiol to provide a constant feedback on LH secretion. Under natural-simulate photoperiod, LH increased in males at 7.0±0.3 wk when days were lengthening. In females treated similarly, sexual maturity occurred at 27.0±0.8 wk when day lengths were decreasing. The reverse photoperiod had no effect on males, but it delayed the expression of sexual maturity in females. Thus, LH also increased in males at 7.1±0.9 wk, while none of the females maintained under the same photoperiod had elevated LH secretion when the experiment was terminated (32 wk of age). Prenatal treatment with androgens masculinized the reproductive response to photoperiod; as in the males, LH increased in the androgenized females maintained under a reverse natural-simulate photoperiod at 7.1±0.4 wk. We conclude that a sex difference in the reproductive response to photoperiod exists in developing sheep and that this is due to the organizing action of testicular androgens during fetal development