Intrauterine position influences anatomy and behavior in domestic rabbits

In several rodent species, the sexual differentiation of a female offspring is known to be affected in utero by the testosterone produced in adjacent male littermates. The aim of this study was to investigate the effect of male neighbors on the sexual differentiation in domestic rabbits. For this, the intrauterine position (IUP) of a female offspring from unilaterally ovariectomized, multiparous mothers was determined by their birth order. Depending on the sex of the adjacent fetuses, pups were divided into 4 groups: 1. Males. 2. 2 M females (females with 2 adjacent males), 1 M females (females with 1 male neighbor), and 0 M females (females with zero adjacent male). Pups' anogenital distance (AGD) was measured at birth and on Day 180 postpartum, when spontaneous chin marking activity was also measured. Our results revealed that AGD was a reliable indicator of sex as male pups had larger AGD than females, both at birth and later on. Adjacent male fetuses had significant effect: the more adjacent male fetuses females have had the longer AGD they possessed. AGD at birth was a good predictor of AGD and behavior of adults, as 2 M does showed the longest AGD and the highest chin marking activity among females. We concluded that, similarly to rodents, proximity to males in utero affects both anatomy and behavior in rabbits.