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J. Dairy Sci. 89:3810-3816
© American Dairy Science Association, 2006.

Presynchronization with Gonadotropin-Releasing Hormone Does Not Improve Fertility in Holstein Heifers

H. Rivera, R. A. Sterry and P. M. Fricke1

Department of Dairy Science, University of Wisconsin, Madison 53706

1 Corresponding author: pmfricke{at}wisc.edu

Holstein dairy heifers were randomly assigned to 1 of 2 treatments to determine whether a presynchronization strategy using GnRH would improve reproductive performance after synchronization of ovulation and timed artificial insemination (TAI). Heifers (n = 82) in the first treatment (GPG) received a hormonal protocol for synchronization of ovulation and TAI (100 µg of GnRH, d 0; 25 mg of PGF2{alpha}, d 6; 100 µg of GnRH + TAI, d 8); whereas heifers (n = 84) in the second treatment (GGPG) received GPG, but with the addition of a GnRH injection (100 µg) 7 d before initiation of the GPG protocol. The proportion of heifers receiving AI before d 8 was similar for GPG (4.9%) and GGPG (9.5%), and the proportion of heifers diagnosed pregnant 30 d after AI did not differ between treatments (45 vs. 51%, respectively). Treatment did not affect the proportion of heifers ovulating after the second GnRH injection or the proportion in which a corpus luteum regressed after treatment with PGF2{alpha}. In conclusion, presynchronization with GnRH 7 d before initiation of synchronization of ovulation using GnRH and PGF2{alpha} did not affect the proportion of heifers expressing estrus before TAI or improve synchronization response or fertility to the synchronization protocol.

Key Words: presynchronization • gonadotropin-releasing hormone • dairy heifer • timed artificial insemination




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