Rising overnight temperatures escalates risk of heat stress in cattle

As spring arrives and temperatures begin to rise, ventilation in livestock buildings gains importance. The Wisconsin Initiative on Climate Change Impacts reports that the average summertime lows in Wisconsin have increased by 5.4 degrees since 1970, exceeding the national average rise of 2.6 degrees.  Such a rise in overnight temperatures escalates the risk of heat stress in cattle by limiting their chance to cool off during the night. Consequently, improving ventilation becomes a key strategy for mitigating heat stress and maintaining the productivity of the animals. However, it should be noted that ventilation fans vary significantly in their design and effectiveness.

When purchasing a ventilation fan, a variety of factors come into play such as:

Ventilation rates: The size and number of fans are determined based on the air exchange requirements of the dairy buildings, typically aiming for 40-60 air exchanges per hour for lactating dairy cows during summer.

Ventilation efficiency ratio (VER): Just as cars are compared based on their fuel efficiency, ventilation fans are chosen based on the energy they use for the amount of air they move, measured in watts per cubic foot per minute (watt/CFM). The BESS Laboratory at the University of Illinois at Urbana-Champaign is one of the certified labs in the US that evaluates livestock ventilation fan efficiency. They provide VER values for various fans at different static pressures on their website (http://bess.illinois.edu). Generally, variable speed fans with larger diameters that do not operate at full capacity offer the best efficiency. Before purchasing a fan, it is recommended to check its VER value to guarantee energy-efficient performance.

For instance, on a farm with 700 cows, using a summer ventilation rate of 1,000 cfm per cow and a fan with a VER of 16 cfm/watt, the ventilation costs could reach about $8,000 for the summer. However, choosing a different fan model of the same size but with a higher VER of 18.9 cfm/watt could reduce costs to $6,800. This change would result in savings of $1,200 every summer, in addition to environmental benefits.

However, efficiency is not the only concern. Choosing a ventilation fan also involves balancing initial cost, durability, service, warranty, and lifetime of the fan.   

Nesli Akdeniz is Assistant Professor and Extension Specialist, Biological Systems Engineering, University of Wisconsin-Madison