Cattlemen's Day, 2000; Kansas Agricultural Experiment Station contribution; no. 00-287-S; Report of progress (Kansas State University. Agricultural Experiment Station and Cooperative Extension Service); 850; Beef; AI; Estrus synchronization; Timed AI; GnRH; MGA; Heifers


We examined the potential of adding gonadotropin-releasing hormone (GnRH) to a synchrony system based on melengestrol acetate-prostaglandin F2a (MGA-PGF2a) to increase the precision of synchronized estrus and augment timed artificial insemination (AI). Yearling heifers were fed MGA daily for 14 days. Nineteen days after the last feeding of MGA, all heifers were given PGF2a (day 0). Heifers receiving no further treatment served as the untreated controls. In the second treatment, heifers also received an injection of GnRH on day –7. Both groups of heifers were artificially inseminated 12 hours after detected estrus. Heifers in the third treatment received GnRH on day –7 and day 2 and were inseminated (timed AI) at the time of the second GnRH injection. In comparison to a MGA-PGF2a synchronization system, addition of GnRH on day –7 did not improve the synchrony of estrus. Adding two injections of GnRH (day –7 and day 2) facilitated timed AI. However, pregnancy rate for timed AI was lower than pregnancy rate for AI 12 hours after detection of estrus.


Rights Statement

In Copyright - Educational Use Permitted.

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.