Breeding Heat-Tolerant Dairy Cows: Production vs. Fertility

As global temperatures increase, selecting dairy cows that maintain both productivity and reproductive performance under heat stress is critical. This study examined more than 100,000 Holstein cows in Spain to quantify the effects of heat stress on milk and protein yield, fertility, and their genetic correlation. Results show that the negative association between production and fertility weakens at higher temperatures, indicating that cows excelling in one trait under heat stress are not genetically predisposed to underperform in the other. The findings support using routinely collected milk and protein yield data alongside fertility responses in breeding programs to identify genuinely heat-adapted animals.