Post-partum oestrus in the sow in relation to the concentration of plasma oestrogens

Ten sows, three entire and seven which had been ovariectomized at different stages of late gestation, were observed for post-partum oestrus. Serial blood samples were collected from six sows during the pre-and post-partum periods, and plasma oestrogen concentrations determined by radioimmunoassay. Morphological aspects of ovarian activity in the entire sows were examined at laparotomy and at autopsy. Although peak values of oestrogen concentration in the plasma varied from 3-9 to 8-0 ng/ml between individuals, the pattern of oestrogen levels was similar for control and ovariectomized sows. Peak concentrations occurred just before parturition, and the timing of ovariectomy did not affect the incidence of the oestrogen peak. Oestrus was detected in one control and one ovariectomized sow at 46 and 40 hr post partum respectively, there being no evidence of ovarian activity in the entire sows. The occurrence of post-partum oestrus in a sow ovariectomized at Day 108 of gestation indicates that this phenomenon is not directly connected with ovarian secretion of oestrogens. The post-partum oestrus is apparently a result of the peak of feto-placental oestrogens that occurs at parturition.