Published on 6/27/2026
A recent scientific study revealed that the effect of heat stress on dairy cows is not limited to reducing the amount of milk only, but also extends to a decline in the quality of the milk in terms of its fat and protein content, which doubles the economic losses on the dairy industry.
According to the study published in the journal Environmental Research Letters, researchers found that rising temperatures lead to a gradual “dilution” in the concentration of essential nutritional components in milk, even before reaching the temperature levels at which production quantities begin to decline sharply.
“This effect occurs almost imperceptibly,” said the study’s lead researcher, Dr. Ariel Ortiz-Popea, an associate professor at the Deason College of Applied Economics and Management at Cornell University, in an official press release, explaining that “the economic losses resulting from a decline in milk quality are close to those resulting from a decrease in production, which means that the actual damage to farmers is doubled.”
The study relied on analyzing huge data that included about 6.5 million cows during the period between 2007 and 2016, in addition to accurate climate data covering 43 American states, where changes were monitored at the level of small geographic networks with an accuracy of up to 4 kilometers.
The results showed that milk production decreases clearly when a certain threshold of temperature and humidity is exceeded, while the quality of milk begins to decline at lower temperatures, and gradually gets worse as the temperature rises, even on days in which there is no decrease in the quantity of production.
Effect throughout the year
“This effect occurs throughout the year and not just in the summer, in contrast to the decrease in production that is usually associated with heat waves,” said co-researcher Jason Prieto.
The study estimates that a 10-point increase in the temperature and humidity index leads to a decrease in milk production by about 1.2%, but it causes a decline in revenues of up to 2.8% annually, equivalent to losses of approximately $1.65 billion in a sector that represents about 20% of livestock production in the United States.
The results also indicate a clear absence of the ability of cows to biologically adapt to heat across generations or regions, as no significant differences were recorded between ages, farm sizes, or geographical regions, except for a clear trend towards the concentration of cow breeding in cooler regions such as New York and Wisconsin.
The researchers hope that these results will contribute to redirecting development efforts in the dairy industry, so that they do not focus only on increasing production, but also on enhancing the resistance of cows to climate change, with the possibility of using more accurate data in the future to determine the most heat-tolerant cows and improve production breeds.
