Effects of intrauterine position during gestation on specific endocrine and behavioral parameters that impact reproduction in domestic rabbits.

Prior studies from others, performed in a different breed, reported that doe rabbits developing between two male siblings (2 M) during gestation display characteristics indicative of masculinization: larger anogenital distance (AGD), larger submandibular glands, and higher chinning frequency than females with zero (0 M) or one (1 M) contiguous brothers. Similar effects are provoked by injecting androgens to the pregnant doe suggesting that prenatal androgen exposure masculinizes female embryos. To further understand the scope of such masculinization we compared 0 M, 1 M, and 2 M females regarding behavioral, neuroendocrine, and somatic parameters, related or not to reproduction. IUP did not impact: body weight, sexual receptivity, mating-induced LH secretion, maternal nest-building, litter size, or milk output. At puberty: a) chinning frequency was: 0 M and males>1 M and 2 M; b) ambulation in open field was lowest in 1 M females and males. IUP effects on AGD were significant only on postnatal day 1: 0 M, 1 M, and males>2 M, in contrast to earlier study. Willingness to nurse at delivery was less frequent in 2 M than in 1 M and 0 M does and correlated with nursing occurrence across lactation. Does that did not nurse at parturition delivered fewer kits/min than those that nursed then, regardless of IUP. The duration of nursing bouts across lactation was significantly longer in the1 M and 2 M does that showed this behavior on postpartum days 1-20. Our findings indicate that IUP is associated with alterations in specific aspects of postpartum maternal behavior.