Estradiol, progesterone, and prolactin regulate maternal nest-building in rabbits

Maternal nest-building in rabbits, expressed across the last third of pregnancy, consists of: digging a burrow, collecting straw and shaping it into a nest inside the burrow, plucking body hair and lining the straw nest with it. The sequential expression of these activities is correlated with specific changes in the plasma concentration of estradiol, progesterone (P), and prolactin (PRL). To further substantiate the participation of these hormones in the control of maternal nest-building we explored in ovariectomized (ovx) New Zealand white rabbits the capacity of several combinations of such hormones to stimulate digging, straw-carrying, and hair-pulling. Does given estradiol benzoate (EB; 5 micrograms/day from days 3 to 21) plus P (2 or 10 mg/day from days 4 to 16) dug into a substrate from the fourth day of the P treatment until withdrawal of this hormone. The intensity of this effect was greater in the group treated with the high dose of P. Straw-carrying and hair-pulling occurred after P withdrawal in a dose-response way. Food intake, which declines in pregnant females shortly before parturition, decreased to the same extent in both groups of ovx EB-treated does after P withdrawal. A significant increase in PRL plasma levels was observed on day 9 in does given EB plus 2 mg P/day and at two days following P withdrawal in does given EB plus 10 mg P/day. When such ovx EB/P-treated does were given bromocriptine to block PRL release (1 or 3 mg/Kg/day, from days 11 to 21) the expression of digging was unmodified. By contrast, bromocriptine abolished the display of straw-carrying and hair-pulling, and also prevented the decline in food intake normally following P withdrawal. The addition of ovine PRL to ovx EB/P-treated does given bromocriptine reduced the expression of digging, did not restore straw-carrying or hair-pulling, and provoked a sharp decline in food intake. The possible mechanisms of interaction between PRL and steroid hormones for the regulation of specific aspects of the pregnant doe's physiology and behavior are discussed.