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Turkish Journal of Veterinary & Animal Sciences

DOI

10.3906/vet-0808-22

Abstract

The objective of this study was to evaluate the effectiveness of GnRH PGF-based protocols on reproductive outcome in Holstein heifers. Heifers were randomly assigned to the control group (n = 14), or treatment groups (n = 50) treated with GnRH (day -7) and PGF_{2\alpha} (day 0). Heifers that exhibited estrus were inseminated (Select Synch, n = 34) and heifers that did not exhibit estrus up to 48 h after PGF_{2\alpha} injection received a second GnRH injection and were fixed-time inseminated (Ovsynch, n = 16). Conception rates were 40%, 55.9%, and 31.3%, and overall pregnancy rates (P < 0.05) were 64.3%, 97%, and 87.5% in the control, Select Synch, and Ovsynch groups, respectively. Ovsynch heifers had 1.8 ± 0.5 and 3.2 ± 0.6 ng mL^{–1} of serum P4, versus 3.3 ± 0.5 and 3.8 ± 0.6 ng mL–1 in the Select Synch heifers at the time of the first GnRH and PGF_{2\alpha} injection, respectively. Conception rates were 55.6% and 58.3% when P4 concentrations were high, and were 50% and 25% when P4 concentrations were low at the time of the first GnRH and PGF_{2\alpha} injection, respectively. Dairy heifers synchronized with GnRH and PGF_{2\alpha} should be inseminated when estrus is observed, and heifers that do not exhibit estrus up to 48 h after PGF_{2\alpha} injection should be given a second GnRH injection and fixed-time inseminated 16-20 h later.

First Page

243

Last Page

248

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