Effectiveness of gnrh/pgf 2a- based protocols on reproductive efficiency of holstein heifers
2009
El-Zarkouny, S.Z.
The objective of this study was to evaluate the effectiveness of GnRH/PGF-based protocols on reproductive outcomes of Holstein heifers. Heifers were assigned randomly to either controls (n = 14) or those treated (n = 50) with GnRH (d - 7) and PGF2a (d 0). Heifers that displayed estrus were inseminated (Select Synch, n = 34), and those that did not display estrus up to 48 h after PGF2a injection received a second GnRH injection and time-inseminated (Ovsynch, n = 16). Conception rates were 40, 55.9 and 31.3% and overall mean pregnancy rates (P 0.05) were 64.3, 97.0, and 87.5% for control, Select Synch and Ovsynch heifers, respectively. Ovsynch heifers had 1.8 ± 0.5 and 3.2 ± 0.6 ng/ml of serum P4 levels compared to 3.3 ± 0.5 and 3.8 ± 0.6 ng/ml for the Select Synch heifers at the times of first GnRH and PGF2a injections,respectively. Conception rates were 55.6 and 58.3% when P4concentrations were high compared to 50 and 25% when P4 concentrations were low at the times of first GnRH and PGF2a injections, respectively. Dairy heifers synchronized with GnRH and PGF2a. should be inseminated at detected estrus, and heifers not displaying estrus up to 48 h after PGF2a injection should be given a second GnRH and time-inseminated 16-20 h later.
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