Serum Luteinizing Hormone, Prolactin, Glucocorticoid, and Progestin in Dairy Cows from Calving to Gestation

Abstract

In a survey of 91 Holstein cows, blood serum prolaetin increased from 50___4 ng/ml at 2 to 4 wk before parturition to 234+_14 ng/ml at parturition and fell to 69+_4 ng/ml during the first 6 wk postpartum. Serum luteinizing hormone remained near .5 ng/m] until parturition, then increased to 1.5+_.3 ng/ml at 5 to 6 wk postpartum. In 12 of the same cows, glucocorticoid increased three-fold to a peak at parturition and returned to prepartum values by 1 wk postpartum; progestin fell from 8.0___.6 ng/ml at 1 to 2 wk prepartum to .9___.2 ng/ml at parturition.