title: Effect of gonadotropin-releasing hormone on fertility in repeat-breeder California dairy cows.
abstract: To assess the potential benefit to fertility from gonadotropin-releasing hormone (GnRH) administration to third service cows managed in typical California dairy systems, 963 cows were enlisted from 14 dairies served by 6 veterinary practices. The cows were randomly assigned to receive either GnRH (100 mug) or placebo at the time of the third artificial insemination. Fertility data were entered onto a proprietary microcomputer program common to all six practices, and collated independently by a third party. For the duration of the trial (1 yr), GnRH and placebo-treated cows had 43.2 and 39.3% conception rates, respectively (P=0.35). When treatments administered in summer months (July, August, September) were excluded, conception rates were 48.1 and 41.0%, respectively (P<0.1). The conception rates of cows treated with GnRH in August tended to be lower than those of placebo-treated cows (95% logarithmic confidence intervals of odds ratio = -1.139, 0.377). Between-herd variation in benefit from GnRH was evident, with two dairies showing no benefit, one dairy showing a negative effect, and four showing a range of effects from lightly beneficial to significantly beneficial. First-lactation cows did not benefit at any time from GnRH treatment. The data suggest that GnRH administered to third-service dairy cows under California conditions may result in increased conception rates in non-summer months, but that other unidentified variables may have important influence on the outcome of such treatment.
authors.affiliation: Department of Reproduction, School of Veterinary Medicine University of California, Davis, CA 95616 USA.
authors.forename: R H
authors.initials: RH
authors.lastname: Bondurant
authors.forename: I
authors.initials: I
authors.lastname: Revah
authors.forename: C
authors.initials: C
authors.lastname: Franti
authors.forename: R J
authors.initials: RJ
authors.lastname: Harman
authors.forename: D
authors.initials: D
authors.lastname: Hird
authors.forename: D
authors.initials: D
authors.lastname: Klingborg
authors.forename: M
authors.initials: M
authors.lastname: McCloskey
authors.forename: L
authors.initials: L
authors.lastname: Weaver
authors.forename: B
authors.initials: B
authors.lastname: Wilgenberg