Oophorectomy during different stages of pregnancy in the cow.

Thirteen cows of the Swedish Red and White Breed (SRB) were subjected to bilateral oophorectomy in the period 105–251 days of pregnancy. Eleven of the animals delivered their fetuses before the expected day of parturition, while 2 which were oophorectomized on days 205 and 212 calved at the expected time. Eleven of the cows had retained fetal membranes following abortion/ parturition. Following surgery the peripheral plasma levels of progesterone dropped to levels about 10 % of the pretreatment levels. Animals oophorectomized between days 105 and 157 of pregnancy had a lower postsurgical progesterone concentration than cows operated on at days 205–251 of pregnancy. No increase of the peripheral plasma levels of estrone in connection with abortion was seen in cows operated on in early stages of pregnancy (< 200 days) while those operated on in later stages and maintaining the pregnancy for at least 17 days post oophorectomy showed an increase of estrone before parturition. The 2 cows that calved at the expected time had an increase of prepartum estrone similar to that seen at spontaneous calving.