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

Abstract

In a survey of 91 Holstein cows, blood serum prolactin increased from 50±4ng/ml at 2 to 4 wk before parturition to 234±14ng/ml at parturition and fell to 69±4ng/ml during the first 6 wk postpartum. Serum luteinizing hormone remained near .5ng/ml until parturition, then increased to 1.5±.3ng/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±.6ng/ml at 1 to 2 wk prepartum to .9±.2ng/ml at parturition.During diestrus of the first postpartum estrous cycle, luteinizing hormone (23 cows) was 50% higher and progestin (9 cows) was 34% lower than during the second cycle. During the 18 days following inseminations, luteinizing hormone was 22% lower in fertile than in infertile cows. Progestin concentration was similar until day 11 in fertile and infertile cows; thereafter, progestin in nine pregnant cows increased to 12.2±2.1ng/ml at day 20, whereas in nine nonpregnant cows progestin peaked at 7.8±.6ng/ml at day 15 and declined thereafter to the next estrus. Correlations within day between luteinizing hormone and progestin were mostly positive in fertile cows, in contrast to the analogous correlations which were mostly negative in open cows.