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Changes of Luteinizing Hormone and Progesterone for Dairy Cows After Gonadotropin-Releasing Hormone at First Postpartum Breeding¹

1675 Observatory Drive, University of Wisconsin, Madison 53706

⁴ To whom reprint requests should be addressed.

ABSTRACT

Gonadotropin-releasing hormone administered at breeding enhances fertility of dairy cows, so a study was designed to evaluate the mechanism for enhanced fertility following administration of gonadotropin-releasing hormone at first postpartum breeding. Twenty-four cows were assigned randomly to one of two treatments, 100 µg of gonadotropin-releasing hormone intramuscular or saline vehicle intramuscular at insemination. Blood samples for luteinizing hormone assay were taken at 2-h intervals prior to breeding and .5-h intervals for 3 h after insemination. Composite morning milk samples for progesterone assay were collected for 30 days after insemination or until next estrus. Cows given gonadotropin-releasing hormone had higher luteinizing hormone concentrations in blood serum following treatment than cows given saline, 13.2 versus 3.0 ng/ml. There was no relationship between luteinizing hormone and subsequent conception. Progesterone for cows that became pregnant was higher throughout sampling days. Mean progesterone concentrations were 4.6 versus 2.2 ng/ml in pregnant and nonpregnant cows during the first 4 days after insemination. Cows treated with gonadotropin-releasing hormone that conceived had higher progesterone than other cows, and that was evident at the first 4 days postbreeding.

¹ This research was supported in part by the University of Wisconsin College of Agricultural and Life Sciences Cooperative Research Grant 049, the United States Department of Agriculture, and CEVA Laboratories, Overland Park, KS.

² Department of Dairy Science.

³ Department of Meat and Animal Science.