Quantifying impacts of extreme heat on cows’ milk production

Farmers likely know that extreme heat can impact the performance of dairy cows, but more research has been emerging lately that helps put better metrics on the effects — quantifying it so that better responses can be implements. One recent study, for example, shows that extreme heat reduces milk production by up to 10 percent and adding cooling technologies only offsets about half of the loss.

And the international research team is pointing to climate change for the worsening weather that producers are facing.

Many recent studies show that climate change will cut crop production, but there has been less research into its impacts on livestock. So while dairy farmers already know their cows are vulnerable to heat, what could more heat mean?

In one of the most comprehensive assessments of heat’s impact on dairy cows, a study in the journal Science Advances finds one day of extreme heat can cut milk production by up to 10 percent. The effects of that hot weather can last more than 10 days later, with efforts to keep cows cool being insufficient.

“Climate change will have wide-ranging impacts on what we eat and drink, including that cold glass of milk,” said one of the study’s co-authors, Eyal Frank, an assistant professor at the Harris School of Public Policy at the University of Chicago. “Our study found that extreme heat leads to significant and lasting impacts on milk supply, and even the most high-tech, well-resourced farms are deploying adaptation strategies that may be an insufficient match to climate change.”

Frank and his co-authors studied the dairy industry in Israel, an advanced dairy system representative of top milk producing countries. The researchers analyze highly local weather data to measure humid heat’s impact on more than 130,000 Israeli dairy cows over 12 years. They then surveyed more than 300 dairy farmers to see how much cooling technologies have helped.

“The dairy industry in Israel is a good testbed because farms are scattered throughout the country and experience a wide range of temperatures and humidity that represent conditions for top milk producing countries around the world,” says co-author Ram Fishman, an associate professor of Public Policy at Tel Aviv University. “Plus, almost all farmers have already adopted ventilation and spraying systems to keep their cows cooler. What’s more, Israeli dairy farms are some of the most technologically advanced in the world, so whatever impacts they suffer are likely greater in other regions.”

The team of researchers found that milk production declined significantly on hot, humid days — by up to 10 percent when wet-bulb temperatures exceeded 26°C (78.8°F).

Wet-bulb temperatures combine information on dry-bulb temperature (the ambient air temperature) and humidity. By doing so, they offer a measure that better captures heat stress. The same ambient air temperature feels very different on dry or on humid days for people and cows. When cows are exposed to this humid heat, often referred to as “steam bath” conditions, it takes more than 10 days for milk production to bounce back to normal levels. While nearly all of the farms the researchers surveyed had adopted cooling technologies, these efforts to adapt only offset about half of the losses on 20°C days (68°F). The hotter it gets, the less they help. On 24°C (75.2°F), they offset 40 percent of the losses. Still, the researchers find it is worth it to install cooling equipment, with farmers able to recoup the costs of installing the equipment in about a year and a half.

“Dairy farmers are well aware of the negative impacts that heat stress has on their herds, and they use multiple forms of adaptation,” says co-author Ayal Kimhi, associate professor at the Hebrew University of Jerusalem and vice president of the Shoresh Institution for Socioeconomic Research. “Adaptation is costly, and farmers need to carefully balance the benefits they obtain versus the costs. This is why we see some investment in cooling measures, but not a complete insulation of cows from their environment, which would be far too costly to implement.”

The researchers use their estimates in Israel to show how climate change could affect milk production globally by mid-century, and which countries benefit the most from adaptation. They find that, without cooling, the top 10 milk-producing countries could see average daily milk output decline by 4 percent — with some countries impacted more than others. Three out of the top five producers — India, Pakistan, and Brazil — see greater losses than Israel: between 3.5 percent and 4 percent per cow per day. They are also the countries that benefit the most from cooling.

Yet, even with cooling, the five largest producers (including the United States and China) still see losses between 1.5 percent and 2.7 percent per cow per day.