Folks familiar with the dairy industry may know that recent years have seen record highs in milk production in Wisconsin. In fact, today’s dairy cow produces nearly twice as much milk as a dairy cow produced 40 years ago. But those numbers aren’t the only ones on the rise: Wisconsin summers are getting hotter and longer, putting the Dairyland’s herds at a higher risk of heat stress, and putting the dairy industry’s upward trends in jeopardy.
Luckily, the Laporta Lab at UW–Madison knows that happy, productive cows require more than feed and green pastures. Jimena Laporta PhD’14 is an associate professor of lactation physiology in the Department of Animal and Dairy Sciences in the UW’s College of Agricultural and Life Sciences. Her research focuses on optimizing the milk-production capacity of dairy cows by studying the influences of nutrition and the environment on their prenatal and early-life development, with special attention paid to the implications of heat stress.
“Heat stress” describes the adverse effects of increased core body temperature resulting from overwhelm of the body’s cooling mechanisms. In humans, this is referred to as “heat stroke” and is considered the most severe form of heat illness. The average human is most at-risk for heat stroke as temperatures near 88 degrees Fahrenheit. Cattle, however, begin to experience heat stress when temperatures reach 70 degrees Fahrenheit — what a human Wisconsin resident might consider a comfortable late-spring or early-summer day.
“A mature cow [weighs around] 1,600 pounds, and they have a rumen that generates a lot of heat,” Laporta says. “Making milk is an energetically demanding process, so [cows’] temperature thresholds are very different [than humans’].”
And as human Wisconsin residents know, summer temperatures don’t peak at 70 degrees. According to the Wisconsin State Climatology Office, Wisconsin’s average summer highs were 75–85 degrees Fahrenheit between 1991 and 2020. Looking ahead, the Wisconsin Initiative on Climate Change Impacts predicts that extreme-heat days (exceeding 90 degrees Fahrenheit) will triple and that evenings 70 degrees and warmer will quadruple by 2050.
This spells not only extreme discomfort for dairy cattle but also long-term consequences for the dairy industry. By collecting samples of blood, tissue, and milk from cows at the Dairy Cattle Center and the Arlington Agricultural Research Station, the Laporta Lab has found that on top of negatively impacting overall animal welfare, heat stress can reduce milk production and quality in both lactating and nonlactating cows by up to 30 percent.
Nonlactating “dry” cows include pregnant cows in their third trimesters as well as heifers, young female cows who have not yet produced their first offspring. These dry cows have historically been overlooked in studies on bovine heat stress, but they’re of particular interest to Laporta. As a lactation physiologist, she is especially interested in the development of the mammary gland, or udders, before the cow reaches milk-producing age (two years old).
“We know that heat stress impacts cows that are making milk because you can see it in the farmer’s pocket in the reduction in milk,” Laporta says. “The problem with nonlactating or younger animals is that you don’t see it right away, so it’s long-term effects are going to come later on.”
According to her research, exposure to heat stress both in-utero and during a heifer’s preweaned phase can lead to compromised immune systems, infertility, stunted mammary-gland growth, and reduced future milk production. These effects can also be passed down through generations.
In short, cooling cows — especially nonlactating members of the herd — is increasingly important to the continued success of dairy farmers everywhere. Luckily, where there are cows, there are collaborators: Laporta works with producers as far as France and as local as Wisconsin to share her lab’s findings on heat-abatement strategies and to hear directly from farmers about the challenges facing their herds.
“Their input really guides us to ask different questions and research different areas … I always come back with new ideas,” Laporta says. “It’s [also] great to hear from them because some of them approach you and they say, ‘I changed the management of my dry cows,’ or ‘I'm doing this with my calves because [of what you said].’ When you see that, you can sense firsthand that you're having an impact.”
