Over the last three decades, the average U.S. temperature has climbed 1.2°F to 1.8°F. During an Iowa State University Extension webinar, Nesli Akdeniz explained why that — and other changes in our weather — are important to recognize when dairy farmers are evaluating how to ventilate their barns and cool cows.
Akdeniz, an assistant professor and extension specialist in biological systems engineering at the University of Wisconsin-Madison, noted that the average temperature in the Midwest was 1.3°F to 1.7°F higher in 2020 than 1991. That climb means dairy farmers must work harder to mitigate the effects of heat stress on their animals.
Making that even more difficult is the fact that in addition to higher ambient temperatures, Akdeniz said that the greater precipitation that we have also experienced leads to more humidity in the environment and warmer nights. This latter concern prevents cows from being able to cool down overnight even if the daytime temperature initiated heat stress.
Further, Akdeniz said that changing temperatures can lead to changing wind patterns. The Intergovernmental Panel on Climate Change predicts a 10% decline in wind speed by 2100, depending on temperatures and land uses, she explained. There are also some research studies that suggest wind speeds will rise in the Midwest, which would be advantageous for farmers operating with naturally ventilated barns. Though wind change is not an immediate concern for Akdeniz, she encouraged farmers to recognize the potential for shifts in our environment as we think about how to effectively cool cows.
Cooling options
Dairy farmers typically utilize one of three types of barns that have different approaches to cooling cows: naturally ventilated, tunnel ventilated, and cross-ventilated.
Natural ventilation will work very well when the barn is placed on a hill, away from other buildings, and oriented east to west, Akdeniz said. She noted that adjacent buildings can have downwind effects blocking wind of up to 10 times their height.
The engineer also described how a roof with a lower pitch will trap warm and moist air and lead to slower air movement. A higher pitch will be more expensive, but it will improve total airflow.
Of course, the limitation with these barns is that you can be at the mercy of Mother Nature. “If there is no wind moving through, it is difficult to ventilate these barns,” Akdeniz said. That’s where circulation fans and sprinklers are needed to help cool cows in very hot weather.
Tunnel ventilation is an option that can sometimes be paired with natural ventilation, she continued. Because tunnel ventilation moves air from one end of a barn to the other, it can provide additional airflow during hot weather for barns that are naturally ventilated during the winter but have lower roofs preventing good air movement in the summer.
Of course, tunnel ventilation can also be a year-round approach. Akdeniz advised having circulation fans over the cow pens to move air through the entire barn. She noted that ridge vents can provide further airflow in these environments.
Finally, cross-ventilated barns are typically more square than the rectangular naturally and mechanically ventilated barns and rely on exhaust fans to generate airflow. While these barns generally don’t have circulation fans, Akdeniz highlighted the value of baffles to push the flowing air down into the cow lying space. “They are a genius idea. They don’t consume any energy, but they work very well,” she said.
In these barns, Akdeniz advised farmers to consider ventilation efficiency ratio before purchasing fans. That relates how much air is pulled through the barn to the electricity the system uses.
To summarize, Akdeniz noted that we are moving toward precision ventilation — not just cooling the whole barn but focusing efforts on where the cows are. This will be critical to keeping cows productive and energy costs reasonable as farmers work harder to offset heat stress.
