Triple-digit temperatures scorched a large portion of the country this summer. Heat stress conditions cause immediate discomfort. However, they also cause long-term consequences on dairy cattle reproductive efficiency. These include a decrease in the length and intensity of estrus, reduced conception rates, decreased embryo survival, reduced pregnancy rates and smaller calf size.
It's important to keep close watch on heifers in the breeding pen - even after heat stress dissipates. If heifers are not meeting Gold Standards II breeding goals during and after times of heat stress, it may be a wake-up call to increase heat abatement measures on your operation.
Aim for these goals for Holstein heifers:
- Begin breeding at 13 to 15 months of age. Strive for a weight of 825 to 900 pounds, hip height greater than 48 inches and wither height of 50 inches (or at 55% of the weight of mature cows in the herd.)
- Inseminate at least 80% of heifers within the first 21 days of moving them into the breeding pen.
- Achieve greater than 70% first-service conception rate with conventional semen and 7 to 12% less with sexed semen.
- Strive to have 85% of heifers pregnant after three heat cycles.
- Freshen heifers at 22 to 24 months of age.
The reproductive performance of heifers can benefit from shade, sprinklers, fans and other cooling practices. Heat-abatement practices are particularly critical when the Temperature Humidity Index (THI) meets or exceeds guidelines identified in the Housing section of the Gold Standards II.