The Thai Journal of Veterinary Medicine


The objective of this study was to determine the reproductive efficiency of lactating dairy cows by using a synchronized ovulation program (Ovsynch). Multiparous, crossbred, Holstein-Friesian cows (40-70 d postpartum; n=60) were divided into a control group (n=30) and an Ovsynch group (n=30), according to their calving dates. Cows in the control group were artificially inseminated according to the AM/PM rule following the detection of standing estrus. The Ovsynch cows were injected with 100 μg GnRH at various stages of the estrous cycle on the first day of the program. Seven days later, they were injected with 500 μg PGF2α, followed by a second injection of 100 μg GnRH, 48 hrs later. AI was carried out 16-18 h after the second GnRH injection. The first service pregnancy rate at 90 d postpartum was not significantly different (30.0% vs.13.3%) for both the Ovsynch cows and the controls (p> 0.05). The overall pregnancy rate at 90 d postpartum was higher in the Ovsynch cows than in the control cows (40.0% vs.16.7%; p< 0.05). Calving to the period from the first AI was shorter in the Ovsynch group than in the controls (63.8±2.18 vs.81.4±5.72 d; p< 0.05). The calving to conception interval in the first AI group tended to be shorter for the Ovsynch cows than for the controls (61.33±3.95 vs. 78.29±9.87d) although the difference was not significant. The conception rate after the first service was similar in both the Ovsynch (30%) and the control groups (20%). In conclusion, the Ovsynch program can be used to improve reproductive efficiency by increasing the estrus submission rate, the overall pregnancy rate at 90 days postpartum, and by reducing days to first service.

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