Conception rates for standing estrus and fixed-time insemination in dairy heifers synchronized with GnRH and PGF2a

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 PGF2a (day 0). Heifers that exhibited estrus were inseminated (Select Synch, n = 34) and heifers that did not exhibit estrus up to 48 h after PGF2a 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 PGF2a 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 PGF2a injection, respectively. Dairy heifers synchronized with GnRH and PGF2a should be inseminated when estrus is observed, and heifers that do not exhibit estrus up to 48 h after PGF2a injection should be given a second GnRH injection and fixed-time inseminated 16-20 h later.

Anahtar Kelimeler:

Key words: Heifers, conception rates, progesterone, Ovsynch, Select Synch

Conception rates for standing estrus and fixed-time insemination in dairy heifers synchronized with GnRH and PGF2a

Keywords:

Key words: Heifers, conception rates, progesterone, Ovsynch, Select Synch,

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