Onset of sexual maturation in female mice as measured in behavior and fertility: Interactions of exposure to males, phytoestrogen content of diet, and ano-genital distance

Age of puberty was examined in female mice through non-invasive behavioral and fertility measures, in relationship to ano-genital distance, phytoestrogen content of diet, and exposure to males post-weaning. Throughout gestation and post-natal development, females were exposed to a regular diet or one that was nutritionally similar but deficient in phytoestrogens. After segregation at weaning on the basis of a short or long ano-genital distance index (AGDI), an indirect measure of in utero androgen exposure, females were housed alone or underneath two outbred adult males for two weeks. Subsequently, an outbred male was placed in the cage of each developing female, and mating behavior, escape attempts, biting gestures, and boxing postures were recorded. Next, females were monitored for the occurrence of a copulatory plug and allowed to bear young, with pregnancy and litters monitored up to weaning. Male-exposed females fed a regular diet were immediately sexually receptive when housed directly with males, and their conceptions occurred earlier than did those of other females. Subjects fed a diet deficient in phytoestrogens were least likely to show sexual receptivity. Male-exposed females with longer AGDI displayed more escape attempts in the presence of males, regardless of diet. Once inseminated, most females carried to term and the majority of pups survived until weaning. These data suggest that phytoestrogens and AGDI interact with exposure to males in determining age at onset of puberty.