How Heat and Humidity Impact Dairy Cow Fertility and Milk Output

Jenn Hoskins
31st March, 2024

Image Source: Hüsna Kefelioğlu (photographer)

Key Findings

Study conducted on Holstein and Montbeliarde dairy cattle in France
Higher heat (THI) reduces milk yield but increases genetic variation in fertility
Genetic traits for milk production and fertility are mildly to moderately antagonistic

In the realm of dairy farming, the well-being and productivity of cattle are paramount. Yet, as global temperatures rise, farmers are grappling with a pressing issue: how to ensure that dairy cows not only continue to produce milk effectively but also remain fertile in hotter climates. A recent study conducted by researchers at Université Paris-Saclay^[1] addresses this challenge, focusing on the genetic factors that may help dairy cattle withstand the stress caused by increased temperatures and humidity. Heat stress is known to have detrimental effects on dairy cows, influencing their milk production, health, and ability to reproduce^[2]^[3]. Particularly in regions with high humidity, such as the southeastern United States, cows struggle to cool down as their primary cooling methods become less effective^[4]. This not only reduces their milk yield but also their feed intake, which can have cascading effects on their overall health and reproductive capabilities^[4]^[5]. The study from Université Paris-Saclay takes a novel approach by examining how genetic interactions with the temperature-humidity index (THI)—a measure that combines air temperature and humidity to assess heat stress—can influence female fertility in dairy cattle. By analyzing data from two cattle breeds, Holstein and Montbeliarde, the researchers aimed to pinpoint genetic traits that could help cows maintain fertility as THI values increase. The scientists' work involved estimating the genetic-by-THI interactions for female fertility, meaning they looked at how different genetic makeups could influence a cow's reproductive success in various thermal conditions. Furthermore, they evaluated the trade-off between production and fertility that becomes evident as THI values rise. This trade-off is crucial; as farmers select for traits that enhance milk production, they may inadvertently be choosing genetics that make cows more susceptible to heat stress, thereby impairing fertility^[4]. The findings of this study are significant because they suggest that it's possible to select for traits that not only maintain but also improve fertility in hot and humid conditions. This is a ray of hope for dairy farmers who face the dual challenge of meeting production targets while ensuring their cattle can reproduce successfully in an environment that is increasingly hostile due to climate change. In practical terms, these insights could help farmers make more informed decisions when selecting which animals to breed. The goal would be to prioritize genetic traits that confer heat tolerance without sacrificing milk yield. This delicate balance is essential for the sustainability of dairy farming in the face of a warming planet. The study's methods were grounded in statistical analysis, using existing data sets to draw correlations between genetics, THI, and fertility outcomes. While the specifics of the statistical models used are complex, the overarching goal was to identify patterns that could inform breeding strategies going forward. In conclusion, the research from Université Paris-Saclay not only underscores the challenges posed by climate change on dairy farming but also offers a pathway to mitigate its effects through genetic selection. By integrating these findings with existing knowledge on heat stress management^[2]^[3]^[4] and the factors contributing to summer infertility^[5], the dairy industry can adapt and continue to thrive even as the mercury rises. This study is a step toward a future where dairy cattle are not only productive but also resilient to the environmental challenges that await.

Genetics Agriculture Animal Science