Reproductive hormones associated with normal and abnormal changes in ovarian follicles in postpartum dairy cows.

Concentrations of reproductive hormones and ovarian changes were monitored every 4 days during the postpartum period in 35 dairy cows. The cows were classified as either control (22 cows) or cystic (13 cows) based on per rectum examination of the ovaries. Control cows were detected with a corpus luteum after the first postpartum ovulation while in cystic cows, ovarian follicles of at least 2.5 cm in diameter persisted in the absence of a corpus luteum for at least 14 days. The mean postpartum interval to the first follicle 1.5 to 2.0 cm in diameter was about 16 days for both groups. Ovulation was detected earlier postpartum for cows in the control group (18.4 +/- 1.7 days) than for cows in the cystic group (36.3 +/- 2.7 days). Luteinizing hormone in plasma increased during the early postpartum period (days 1 to 10) for both groups, but mean concentrations of luteinizing hormone, progesterone, and estradiol-17 beta in plasma were not different between groups then or on days -8, -4, or 0 (day of the first postpartum follicle 1.5 to 2.0 cm in diameter). During this period (days -8 to 0), estradiol-17 beta and luteinizing hormone in plasma were correlated positively, but regression coefficients differed between groups. These results suggest a partial hypothalamic and/or pituitary failure in releasing pituitary luteinizing hormone as a cause for postpartum ovarian cysts.