Peripheral plasma progesterone and corticoid levels at parturition in the sow.

Plasma levels of progesterone and corticoids were determined in eight sows prior to, during and following parturition. A statistically significant diurnal variation was observed with morning samples having a higher level of corticoids. Progesterone levels decreased through the last day of gestation to a low level at day 1 postpartum. Mean corticoid levels increased during the last 24-hr. prepartum and returned to prepartum levels within 36 hr. of farrowing. The elevation in corticoid levels is interpreted to be a result rather than a cause of parturition.