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Abstract
Estrus was synchronized in dairy cattle using the synthetic prostaglandin F2a (PG) analog Estnunate (Coopers Animal Health Ltd., Berkhamsed, England. UK; 250 ug/ml of cloprostenol). PG was administered by two routes at two different doses, 500 ug by im route (control) and 125 pg by intravulval lip (ivu) route (treatment). All animals were bred by artificial insemination (AI) to detected estrus using the am-pm breeding rule (BR). First service conception rate (FSCR) for all dairy cows and heifers was 70% for the control and 54% for the treatment groups (P>0.05). The FSCR was also not different (P>0.05) between Holstein (HOL) and Australian Milking Zebu (AMZ) breeds (HOL 52% and AMZ 78%). Moreover, all the animals in this study were confirmed pregnant by the end of the breeding season. In conclusion, dairy cows and heifers can be successfully synchronized using only 125 pg of cloprostenol without impairing fertility. This dose corresponds to only one fourth of the recommended dose of 500 pg of cloprostenol by the manufacturer.