Conclusions
There is no benefit in terms of precision of estrus, conception rate or pregnancy rate from the addition of a single injection of GnRH on day _7 to the MGA-PGF2a synchrony program. The addition of two injections of GnRH (on day _7 and day 2) permitted timed AI and reduced animal handling; however, this program has the added cost of 2 injections of GnRH/female and equivalent pregnancy rates cannot be attained without the addition of 4 to 7 days of heat detection.
Acknowledgments
We acknowledge the cooperation and participation of Shugert Farms, Lore City, OH, the KSU Agriculture Research Center, Hays, KS and Losey Bros., Agra, KS. Appreciation is expressed to Select SiresÒ, Plain City, OH for financial support of this project. Thanks are also extended to Merial Ò (Iselin, NJ) and Pharmacia and UpjohnÒ(Kalamazoo, MI) for provision of CystorelinÒ and LutalyseÒ, respectively, for this project.
References
Brown, L.N., K.G. Odde, D.G. LeFever, M.E. King, and C.J. Neubauer. 1988. Comparison of MGA- PGF2a to Syncro-Mate B for estrous synchronization in beef heifers. Theriogenology 30:1.
Wood, S.L., M.C. Lucy, M.F. Smith, and D.J. Patterson. 1999. Improved synchrony of estrus with addition of GnRH to a melengestrol acetate (MGA: 14 d) _ prostaglandin F2a (PG: 19 d) estrous synchronization treatment in beef heifers. J. Anim. Sci. 77(Suppl. 1):227.