Abstract:
The objective of this study was to determine the reproductive efficiency of lactating dairy cows by using synchronized ovulation program (Ovsynch). Multiparous crossbred Holstein Friesian cows (40-70 d postpartum ; n=60) were divided into control group (n=30) and Ovsynch group (n=30), according to their calving date. Cows in the control group were Al according to the AM.-PM. rule following detected standing estrus. Cows treated Ovsynch were injected with 100 µg GnRH (Buserelin ; Receptal® ) at random stage of estrus on the first day of program. Seven days later, cows in this group received 500 µg PGF2a(Cloporstenol ; EstroPLAN ® ), followed by a second injection of 100 µg GnRH 48 h later. Al was carried out at 16-18 h after the second GnRH injection. Blood was collected from Ovsynch cows at each hormone injection. Serum was evaluated for progesterone concentration by using RIA. First pregnancy rate by 90 d postpartum were not different (30.0% vs. 13.3% for the Ovsynch cows and control cows respectively). Overall pregnancy rate by 90 d postpartum were higher in Ovsynch cows than control cows (40.0% vs. 16.7% ; p<0.05). Calving to first Al were shorter in Ovsynch group than control (63.8±2.18 vs. 81.4±5.72 d). Calving to conception from the first Al tended to be shorter than for Ovsynch cows than control (61.33±3.95 vs. 78.29±9.87 d). Conception rate at first service were similar for Ovsynch (30.0%) and control (20%). Evaluation of serum progesterone concentration profile indicated that the progesterone level was associated to the outcome of pregnancy. In conclusion, Ovsynch program can improve reproductive efficiency by increasing estrus submission rate, overall pregnancy rate within 90 days postpartum and reducing days to first service.