The Occurrence of Estrus and Ovulation in Postpartum Sows

Data are presented on 36 sows that were checked for a postpartum heat and later killed to determine the condition of the ovaries. Eighteen of the animals came into heat and were bred, but only 2, of the 18 ovulated (pigs dead at birth in one and immediately after birth in the other). None of the nonestrous sows had ovulated when killed 10 days postpartum. An experiment to test the effect of suckling did not show it to be a factor in inhibiting ovulation. There was, however, a lesser follicular volume in suckled sows than in nonsuckled sows. It is suggested that an extra-ovarian source of estrogen is responsible for the postpartum anovulatory heat.