Effects of ovariectomy and progesterone treatment on the maintenance of pregnancy in bitches.

Abstract

To determine the essentiality of the ovary for the maintenance of Pregnancy in the bitch, 18 pregnant bitches were ovariectomized at different times in the second half of gestation period and the occurrence of abortion was examined. The effects of progesterone administration on the maintenance of pregnancy in these ovariectomized animals were also examined. In all of 7 bitches ovariectomized on days 40 to 55 of pregnancy, abortion occurred between 11 and 63 hr after ovariectomy. The interval between ovariectomy and abortion seemed to be shortend with the advance in gestation. Another 6 bitches were ovariectomized during days 39 to 50 and followed by daily administration with 20 to 50 mg of progesterone until day 55 or 61. Pregnancy was maintained without abortion and parturition took place normally in all of these animals. The remaining 5 bitches ovariectomized on day 50 were administered daily with progesterone up to day 62 or later. Four of these 5 animals were delivered of young on days 64 to 66, although atillbirths were seen in 2 animals. These results indicated that the ovary should play an essential role through the secretion of progesterone in the maintenance of pregnancy up to around day 55 in the bitch.