Conception Rate of Pre-synchronization and Two Short Term Heat-synch Programs using Two Doses of PGF2α in Lactating Holstein Dairy Cows

BACKGROUND: Improving the reproductive performance of dairy cows requires estrus manipulation using estrus synchronization protocols. OBJECTIVES: The current study aimed to assess the effect of reducing the length of estrus synchronization pro-tocol by two doses of prostaglandin injection on the reproductive performance of Holstein dairy cows. METHODS: At first, all cows received GnRH (day 0) followed by PGF2α on day 7 and GnRH on day 17. Next, cows were assigned randomly to one of the three groups: Group 1) PGF2α injection on days 22 and 23, estradiol benzoate injection on day 24, Group 2) PGF2α injection on days 23 and 24, estradiol benzoate injection on day 25, and Group 3) Control group; injection of PGF2α on day 24, injection of estradiol benzoate on day 25. Estrus detec-tion was performed twice a day up to 48 h (AM/PM) based on the signs of estrus, and fixed time AI protocol was used after 48 h if not previously inseminated. RESULTS: The conception rate in group 2 was significantly higher than the control group (P≤0.05) and tended to be higher than group 1 (P=0.079). CONCLUSIONS: Our results confirmed the hypothesis that a decline in the period of follicle dominance by re-ducing the interval between GnRH and PGF2α through two PGF2α injections improved the fertility of lactating dairy cows.