Plasma estrogens in the periparturient cow

Six pregnant multiparous beef cows were fitted with indwelling jugular cannulae. On day 277 of pregnancy, blood samples were collected at 4-hr intervals through 46 hr postpartum. Plasma estrogens increased linearly (P<.01) from 399 pg/ml at ?158 hr prepartum to 501 pg/ml at parturition. Postpartum estrogen levels were described by a quadratic equation (P<.05) from parturition to 46 hr postpartum; decreasing rapidly from parturition to 34 hr postpartum (106 pg/ml).