Abstract
Optimized reproduction management enhances fertility of dairy cows, and thus improves their milk production efficiency. Comparing different synchronization protocols under variable ambient conditions would be conducive to protocol selection and production efficiency improvement. Here, 9538 primiparous Holstein lactating cows were enrolled to either Double-Ovsynch (DO) or Presynch-Ovsynch (PO) to determine the outcomes under different ambiences. We found that averaged THI of 21-days before the first service (THI-b) was the best indicators in a total of 12 environmental indexes to explain changes in conception rate. And the conception rate decreased linearly in DO treated cows when THI-b was over 73, whereas the threshold was 64 in cows subjected to PO. Compared with PO treated cows, DO increased conception rate by 6%, 13% and 19%, when THI-b was lower than 64, from 64 to 73, and over 73, respectively. Furthermore, employing treatment of PO would lead greater risk for cows staying open compared with DO when THI-b below 64 (hazard ratio, 1.3) and over 73 (hazard ratio, 1.4). Most importantly, calving intervals were 15 days shorter in DO treated cows compared PO when THI-b over 73, while no difference was detected when THI-b below 64. In conclusion, our results supported that, fertility of primiparous Holstein cows could be improved by employing DO, especially in hot weather (THI-b ≥ 73), and the benefits of DO protocol were abated under cool conditions (THI-b < 64). Considering the impacts of environmental heat load is necessary to determine reproductive protocols for commercial dairy farm.
Published Version
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