Ovulation, estrus and endocrine response after GnRH in early postpartum cows.

Ovulation estrous and endocrine response after the administration of gonadotropin-releasing hormone (GnRH) were studied in 20 lactating cows. The cows received either a (100 GnRH mcg) SUBCUTANEOUS implant or saline on Day 14 postpartum. Serum luteinizing hormone (LH) increased (p less than .05) from 1.9 ng/ml at GnRH administration to 5.7 13.8 and 15 at 1 2 and 4 hours and decreased to 4.7 ng/ml at 6 hours. All cows who received GnRH ovulated on Day 15. The interval to the first postpartum ovulation was shorter (14.4 days; p less than .05) for GnRH-treated cows than for 8 of 10 controls (23.6 days). Estrogens and progesterone were not acutely affected by GnRH. GnRH did not shorten the interval to first estrus. GnRH induced LH release and ovulation and these cows continued to cycle to Day 65 postpartum when the study was terminated.