Role of rabbit fetuses and placentas in the maintenance of gestation and parturition.

Abstract

Fifteen pregnant rabbits were used to study the effect of fetectomy on length of gestation, maternal nest building, milk ejection, mortality of pups and placental weight. Fetectomy on day 25 post coitum led to normal delivery of the placentas at term, nest building and milk ejection, indicating that the fetuses were not required for maintenance of gestation and initiation of parturition. In a second experiment involving forty pregnant does, the effects of fetectomy (on days 21 and 25) and dexamethasone administration (on days 25 and 26) on length of gestation and on parturition-related variables were investigated. Fetectomy on day 21, despite dexamethasone administration, did not lead to placental delivery at any time. Dexamethasone treatment on days 25 and 26 induced parturition earlier in the presence of the fetuses than in their absence and the induction of parturition increased the number of stillborn pups. Maternal nest building and milk ejection were normal except does fetectomized on day 21 failed to build nests or eject milk. Corpora lutea from does fetectomized on day 21 or 25 weighed less than those from nonoperated does. Within each stage of gestation and each type of surgery, dexamethasone appeared not to have altered ovarian and corpora lutea weights. (Key Words: Rabbit, Fetectomy, Placentas.