Extreme heat makes dairy cows produce less milk

Extreme heat is taking a toll on livestock agriculture. A new study from the University of Illinois Urbana-Champaign examines how heat stress affects U.S. dairy farms.

The researchers found that high temperatures and humidity lead to a 1% annual decline in milk yield. Smaller farms suffer more than large ones, which can adopt management strategies to reduce the effects.

Impact of heat on dairy cows

Study co-author Marin Skidmore is an assistant professor in the Department of Agricultural and Consumer Economics at the University of Illinois.

“Cows are mammals like us, and they experience heat stress just like we do. When cows are exposed to extreme heat, it can have a range of negative physical effects,” explained Professor Skidmore.

“There is an increased risk of infection, restlessness, and decreased appetite, which leads to a decline in milk yield. For dairy producers, the heat impact is a direct hit on their revenue.”

The team studied milk production data from nine Midwest states. They analyzed over 56 million cow-level records from 18,000 dairy farms between 2012 and 2016. The researchers adjusted milk data for protein and fat content to better assess milk quality, which determines its market value.

Heat stress and dairy quality

“Previous studies have focused on fluid milk yield. But in our dairy marketing system, milk is sold on components. When you calculate revenue, it’s not just about how many gallons of milk, but whether it’s high-quality milk with high protein and fat content,” Skidmore said.

The researchers linked milk production records with daily temperature and humidity data. They used temperature-humidity index measurements to gauge how much heat stress cows experience. High heat and humidity make it harder for cows to cool down, leading to reduced milk production.

On average, 1% of annual milk yield is lost to heat stress. That translates to about 1.4 billion pounds of milk over five years for the farms in the study. Based on average milk prices, these losses amount to roughly $245 million in revenue.

Smaller farms suffer more

Most of the losses occur on low- and moderate-stress days, which happen more often.

However, extreme heat days have a much greater impact, causing more than twice the dairy milk loss per cow compared to moderate-stress days.

Smaller farms experience the greatest financial burden. The researchers found that herds with fewer than 100 cows lost an average of 1.6% of their annual milk yield. Though these farms contributed less than 20% of the total output in the study, they accounted for 27% of total damages.

Strategies to combat heat stress

Producers can take steps to reduce heat stress. Open barn sides, fans, and sprinklers can help cool cows.

“There are a number of different adaptive methods, but there is no silver bullet. You can install more sprinklers and sophisticated ventilation systems. You could change the timing of calving to avoid these warmer periods, but that incurs other risks, and it is a complex issue,” noted Professor Skidmore.

Lower levels of heat stress can be managed with current techniques. Large farms experience minimal losses at those levels. However, when temperatures and humidity rise beyond a certain point, no mitigation strategy is fully effective.

Future projections and policy needs

The researchers projected milk yield losses through 2050 using predictions from 22 climate models. The findings suggest extreme heat days will become more common, and milk yield losses could increase by 30%.

If dairy production remains a priority, small farms will need additional support. Professor Skidmore emphasized the importance of financial incentives to help farmers adopt heat mitigation strategies. Further research will also be necessary to manage extreme heat stress.

“If there’s interest in continuing to have a healthy and robust small dairy production presence in the U.S., that probably will require financial incentives to help farmers implement mitigation strategies, as well as investments in further research on how to manage the highest levels of heat stress,” she concluded.

The study is published in the journal Food Policy. The research was funded by a Center for the Economics of Sustainability Seed Grant.

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