Heat stress has often been treated as a summer problem in dairy herds, something producers prepare for when temperatures rise and fans and sprinklers turn on. But nutritionists are pointing to a bigger issue: heat stress can affect cows even after cooler weather returns.
In a recent episode of the Dairy Nutrition Black Belt Podcast, ruminant nutrition expert Brian Campbell talked about how heat stress in dairy cows can have long-term and even multi-generational effects. Those effects are changing how nutrition programs are being built.
Heat Stress Goes Beyond Summer
“When you start looking at the dairy cow and the impact of heat stress, there’s multi-lactation impacts,” Campbell explains. “There’s also multi-generational impacts from heat stress.”
He notes the challenge with heat stress is that the damage does not end when temperatures drop. Studies continue to show heat stress can have lasting effects on cow performance, impacting production well beyond a single lactation and potentially affecting the next generation.
Nutrition is an important tool in managing heat stress, helping support cows through changes in intake, digestion, metabolism and overall performance. But Campbell says there is no single answer.
“There’s lots of options out there,” he says, referencing additives like essential oils, osmolytes, chromium and yeast products. “But heat stress impacts so many different areas of the animal and so many different systems. There’s really no silver bullet.”
No Silver Bullet Solution
Heat stress does not affect just one part of the cow. It can lower feed intake, affect hydration, change rumen function and reduce milk production at the same time. Because of that, products that focus on only one area may not be enough.
Instead, more nutrition programs are using several tools together.
“It’s not going to make it go away completely,” Campbell says. “But there are lots of options out there and we’re reducing the impact.”
Those tools include yeast-based products, chromium and osmolytes such as betaine. Each may help support cows during heat stress in a different way.
Yeast Supports Rumen Health
When cows become heat stressed, they typically eat less and often change their feeding patterns, consuming larger meals during cooler parts of the day. This can put extra stress on the rumen, increasing the risk of acidosis and reducing feed efficiency.
According to Campbell, yeast products, particularly live yeast and yeast culture additives, are designed to support a more stable rumen environment by encouraging beneficial microbial populations and improving fiber digestion. Research has shown these products can help maintain rumen pH, support dry matter intake and improve nutrient utilization, all of which become increasingly important when cows are under heat stress.
Campbell says yeast may offer another hidden benefit: reducing the amount of heat generated during the fermentation process itself.
“When you look at fermentation, there’s heat that’s produced from fermentation itself,” Campbell explains. “If we can improve that fermentation, we get less heat of fermentation produced. So, it’s less overall heat on the animal.”
By creating a more efficient rumen, cows can extract more nutrients from every pound of feed they consume while generating less excess heat.
“Anything we can do to improve the overall health of the animal is going to allow that animal to better deal with stress,” Campbell says.
Chromium and Energy Use
Chromium, a trace mineral widely studied in the 1990s, is again getting attention as researchers look for ways to limit production losses during heat stress. While Campbell notes he is not a chromium specialist, he points to research showing how chromium can influence glucose metabolism, helping cows use energy more efficiently when they are under stress.
Heat-stressed cows typically reduce feed intake as they try to limit the amount of heat generated through digestion.
“One of the first things you see is a reduction in intake, which drives down their ability to produce milk,” Campbell says. “With chromium, we’re helping to maintain that milk production during those heat stress times.”
Researchers believe chromium’s role in insulin function and glucose utilization may help cows make better use of available energy when nutrient intake declines. While it doesn’t eliminate the effects of heat stress, Campbell says chromium can help reduce some of the production losses commonly seen during periods of high temperatures, allowing cows to maintain production more effectively despite the challenge.
Betaine at the Cell Level
Betaine is another ingredient nutritionists are using more as they look for ways to help cows cope with heat stress. Unlike some feed additives that mainly target rumen function or metabolism, betaine works at the cellular level.
Betaine functions as an osmolyte, meaning it helps cells regulate and retain water during stressful conditions. As cows experience heat stress, maintaining hydration becomes important not only for overall health but also for milk production, feed intake and normal cellular function.
“It’s going to help maintain hydration at the cellular level,” Campbell says. “It helps maintain moisture within the cell and supports the cell membranes.”
By helping cells hold water and maintain their structural integrity, betaine may help cows better withstand the physiological strain caused by elevated temperatures. This becomes especially important during extended periods of heat stress, when cows can struggle to stay hydrated and maintain normal body functions.
Campbell notes that betaine works differently than products designed to improve digestion or milk production directly. Instead, its role is to support the animal’s ability to maintain normal cellular function during stressful conditions
Why Nutrition Tools Stack
Using more than one nutrition strategy is becoming more important than relying on a single product. Campbell compares it to a “multiple hurdle” approach, where several steps work together to deliver a stronger overall result.
“If the animal is getting impacted in multiple locations, you need a solution that also works in multiple ways,” he says.
That’s where combination strategies come in. Instead of just stacking individual benefits, well-designed nutrition programs aim to make the whole system perform better than any one ingredient alone.
“The idea isn’t 1 + 1 + 1 = 3,” he says. “It’s 1 + 1 + 1 = 5.”
As more research points to the longer-term effects of heat stress, more attention is going toward nutrition programs that help cows stay productive across lactations and support future performance.
