Hamid Ghasemzadeh-nava - Department of Theriogenology, Faculty of Veterinary Medicine, University of Tehran, Tehran-Iran
Mirmoein Bahrami - Department of Theriogenology, Faculty of Veterinary Medicine, University of Tehran, Tehran-Iran
Vahid Akbarinejad - Department of Theriogenology, Faculty of Veterinary Medicine, University of Tehran, Tehran-Iran
Seyed Alireza Alavi Tabatabaee - Theriogenologist and Private Practitioner, Tehran-Iran

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 ۰) followed by PGF۲α on day ۷ and GnRH on day ۱۷. Next, cows were assigned randomly to one of the three groups: Group ۱) PGF۲α injection on days ۲۲ and ۲۳, estradiol benzoate injection on day ۲۴, Group ۲) PGF۲α injection on days ۲۳ and ۲۴, estradiol benzoate injection on day ۲۵, and Group ۳) Control group; injection of PGF۲α on day ۲۴, injection of estradiol benzoate on day ۲۵. Estrus detec-tion was performed twice a day up to ۴۸ h (AM/PM) based on the signs of estrus, and fixed time AI protocol was used after ۴۸ h if not previously inseminated. RESULTS: The conception rate in group ۲ was significantly higher than the control group (P≤۰.۰۵) and tended to be higher than group ۱ (P=۰.۰۷۹). CONCLUSIONS: Our results confirmed the hypothesis that a decline in the period of follicle dominance by re-ducing the interval between GnRH and PGF۲α through two PGF۲α injections improved the fertility of lactating dairy cows.

Conception rate, Dairy Cows, heat-synch, Short-Term