During an Iowa State University Extension webinar, Jennifer Van Os shared signs that help evaluate the effectiveness of cow cooling strategies. The University of Wisconsin-Madison assistant professor and extension specialist emphasized that observing how animals are coping in hot weather is the only direct indicator of how well the system is working for the cows and to assess if additional intervention is needed.
Cows have several behavioral, intrinsic, and physiological responses to heat stress. If cows are showing certain signs, Van Os said they are thermally uncomfortable and would benefit from some or more cooling tools.
Behaviorally, cows experiencing heat stress are more lethargic. Van Os said cows decrease their activity levels in hot weather to reduce body heat production. Heat-stressed cows will also seek shade, water, and cooling mechanisms. That is why, in hot weather, it is common to see cows bunched around the water trough or standing at the feed alley under the sprinklers but not eating.
Watching for these behaviors can be useful, but Van Os said they need to be observed over time, which is easier done in a research setting. One quick snapshot in time isn’t enough to truly assess the situation.
Other heat stress indicators collected in research settings are skin temperature and sweating rate, but again, these are harder to observe on farms. There are, however, some straightforward ways to watch for heat stress.
“Panting and elevated respiratory rate are the best tools in your tool kit for evaluating heat stress status in cows,” explained Van Os.
Panting is a very visible indicator of heat stress. Van Os said it doesn’t take long to walk past a pen of high-producing cows and tally any panting cows. Signs to watch for are drooling, open-mouthed panting, and panting with the tongue hanging out.
“One limitation of panting is that it is a late sign of heat stress,” Van Os said, noting that these cows are already under a lot of stress. “It can be a useful indicator, but it is not the first thing to watch for.”
An earlier marker of heat stress is respiration rate. As a rule of thumb, dairy cows should be taking less than 60 breaths per minute. If cows are at 60 breaths or more per minute, Van Os said their natural mechanisms of cooling are not sufficient.
When preparing to evaluate a cooling system, Van Os said to first check the weather forecast. Plan to monitor the cows on an intermediate day to get a sense of how the system is working. A cool day will not create the same heat stress challenges. On the other hand, even a very functional cooling system will likely be inadequate during a heat wave. “That is just the reality of it,” noted Van Os.
Also, be sure to evaluate the microclimate in the barn. Many cooling tools, like fans and sprinklers, are activated based on temperature thresholds that should be set based on the condition in the barn. If a barn feels warm but the cows seem comfortable, that is a good sign that cooling strategies are working at the cow level. However, if the barn feels cool but the cows are struggling, that also tells you something, Van Os said.
