Effect of gonadotropin-releasing hormone on clinical response and fertility in cows with cystic ovaries, as related to milk progesterone concentration and days after parturition.

We gave gonadotropin-releasing hormone (GnRH) or an analog of GnRH to 264 lactating cows with cystic ovaries. The effects of milk progesterone concentration (MPC) and days after parturition (DAP) at diagnosis on clinical response 30 days after treatment and on subsequent fertility were examined. Palpation per rectum revealed ovarian cysts in 264 cows; 118 had true follicular cysts (MPC less than 1 ng/ml). Clinicians with more than 3 years of experience reported significantly more true cysts than did less experienced clinicians. Clinical response 30 days after treatment did not differ in 3 groups of cows (divided on the basis of MPC at treatment), but fewer cows with MPC less than 1 ng/ml were bred or conceived than were cows with MPC greater than or equal to 33 ng/ml. Days after parturition at diagnosis did not affect 30-day clinical response rate, but cows treated less than 35 DAP had significantly more days to first estrus and to conception than did cows treated greater than 90 DAP. Significantly more cows treated less than 35 DAP had MPC less than 1 ng/ml at treatment.