Rethinking ventilation

Nothing is certain in the world except for change. With changes in cows, management styles and the climate, dairy barn ventilation needs to change as well.

Dr. Nesli Akdeniz, an associate professor and extension specialist in biological systems engineering at the University of Wisconsin-Madison, shared her thoughts on the changing ventilation needs of dairy farms during a June 13 webinar hosted by the I-29 Moo University.

According to Akdeniz, the ventilation standard in the Midwest Plan Service 32 from the 1990s was 469 cubic feet per minute per cow. That recommendation increased to 1,000-1,500 cubic feet per minute in the UW-Madison Dairyland Initiative published in 2020.

Several factors prompted that increase, Akdeniz said, including advancements in genetics that have created larger, higher-producing cows, as well as changing environmental and climate factors.

“More is not always better — with higher ventilation rate, energy consumption increases,” Akdeniz said. “The more we ventilate, the more greenhouse gas emissions we have. We need to keep that in mind. The more GHG emissions we have, the more we will need to ventilate in the future. It is an endless cycle.”

According to Akdeniz, the average temperature in the Midwest rose as much as 1.7 degrees Fahrenheit over the past 20 years. The region is experiencing more rainfall as well, leading to increased humidity and warmer nights. These factors make dairy cows susceptible to heat stress.

“Heat stress is not just the temperature,” Akdeniz said. “We are talking about temperature plus the humidity, the temperature-humidity index.”

At THI levels of 68-71 degrees, Akdeniz said cows are at a mild risk of heat stress. When THI rises to 72-79 degrees cows are at a moderate risk of suffering the effects of heat stress. Over 80 degrees, the risk of heat stress reaches severe levels, according to Akdeniz.

Increased daytime temperatures coupled with warmer nighttime temperatures can also be problematic for dairy cows, Akdeniz said.

“If we have higher daytime temperatures but it cools down at nighttime, cows can take a break and recover from the heat stress they experience,” Akdeniz said. “If the nighttime temperatures are high, they may be able to recover from one or two days. If it continues for a couple of days in a row, then it makes it difficult for animals to recover from heat stress. They cannot continue to produce.”

While dairy farmers need to keep projected temperature changes in mind when considering ventilation styles for both new constructions and retrofits, Akdeniz also advises them to factor projected future changes in wind speeds and direction in their plans.

“Temperature gradients, ocean-atmospheric interactions and land use changes all play a role in wind patterns,” Akdeniz said. “The Intergovernmental Panel on Climate Change predicts there will be a 10% decrease in wind speeds by 2100, while some studies suggest that wind speeds will actually increase in the Midwest.”

In the Midwest, dairy buildings are typically designed assuming the winds will blow from west to east to take advantage of prevailing winds, Akdeniz said.

“If there will be a shift, if it starts blowing from north to south, it will affect all our ventilation designs, especially naturally ventilated designs,” Akdeniz said.

Because of the influence climate has on cows, creating a positive housing environment is crucial, according to Akdeniz.

“We want all our cows to be outside, on the ground in the fresh air, and enjoying the sunshine, but there are reasons we cannot put most animals outside,” Akdeniz said. “One reason is the climate. It sometimes helps to have a roof on the animals. Sometimes, like last year with severe drought, all our pastures shut down early. This is why we put maybe 90% of our animals indoors.”

In the upper Midwest, Akdeniz said many types of barns and ventilation systems — both natural and mechanical — can work well for providing housing on dairy farms.

“Most of the dairy buildings in Wisconsin are naturally ventilated,” Akdeniz said. “The only concerns are on those extreme heat days. Sprinklers and circulation fans can help mitigate heat stress during times of extreme heat.”

For natural ventilation to work well, Akdeniz said to ensure that parallel buildings are no closer than 100 feet, noting that adjacent buildings can cause downwind effects up to 10 times their height.

“Naturally ventilated buildings need to be able to capture all the prevailing winds,” Akdeniz said. “If there are many buildings around, they block the airflow and natural ventilation does not work anymore.”

Sidewall height and inlets, along with roof pitch and ridge design are all crucial pieces of a well-designed, naturally-ventilated barn that allows for adequate air movement, Akdeniz said.

“Lower pitch means slower air movement,” Akdeniz said. “Moist air is trapped (and) it has a harder time exiting the ridge vents. A higher pitch works like a chimney, drawing it out. Winter might be an exception since there is less heat. But in summer it works well.”

According to Akdeniz, if natural ventilation does not work, the next best option is tunnel ventilation.

“In tunnel-ventilated buildings, the air moves perpendicular to the stalls,” Akdeniz said. “The ventilation fans are placed on the end wall. We want the air to come in from one side and leave the other side.”

In addition to the tunnel fans, Akdeniz said circulation fans are needed throughout the animal area to circulate the fresh air where cows are housed.

“If you don’t have the circulation fans, only the feed alley is ventilated,” Akdeniz said.

Another option for mechanical ventilation is cross-ventilated barns, Akdeniz said. Cross-ventilation uses exhaust fans to pull air that comes in through baffles across the barn and directly over the stalls.

As more producers are utilizing automated milking systems on their farms, Akdeniz urges them to consider ventilation, including dead spots created by automated milking systems and high-traffic areas in their plans.

“Added ventilation and cooling are crucial for the success of AMS facilities,” said Akdeniz.

While increased ventilation is necessary for optimum cow health, Akdeniz said research projects are underway looking at the use of micro-climate ventilation as a way of decreasing overall ventilation needs.

“In a calf barn, we can use positive-pressure tubes to ventilate only the area where the calf is living,” Akdeniz said. “We are looking at ways to do the same with larger animals — to ventilate only the areas where the milking cows are living, rather than ventilating the entire barn.”