When cows are heat stressed, many dairy producers have seen a drop in milk production and feed intake firsthand. They may have also noticed that the cows spend less time at the feedbunk, more time around the water troughs, and that they may bunch together. Astute observers may also have seen cows spending more time standing up instead of lying down. This pattern has been reported in several research studies, even when cows have heat abatement from feedbunk soakers.
My colleague, Nigel Cook, MRCVS, noticed that in the summer, cows on bedded packs show a behavioral pattern where they appear to lie under the air stream from fans. We received a Critical Agricultural Research and Extension grant from USDA to evaluate whether high-speed air from fans could reduce heat stress, not only to protect milk production in the summer but also to promote adequate resting behavior and animal welfare.
First, we did a controlled experiment at the University of Wisconsin-Madison research dairy farm. We calibrated the fans to deliver at least 200 feet per minute of air speed in every freestall, as measured at cow resting height about 20 inches above the stall. We found that, as expected, fans reduced cows’ signs of heat stress by keeping their respiration rates and body temperatures in the normal range. Furthermore, the fans prevented dry matter intake and milk yield from dropping in warm weather compared to when the fans were off and cows only had the natural ventilation of the barn. Most interestingly, though, was that fans over the stalls also kept lying time from decreasing, even on warmer days.
We followed up with an observational study on 12 Wisconsin dairy farms. Six were naturally ventilated facilities, while six were mechanically cross-ventilated barns. At each facility, we measured the air speeds at cow resting height in a sample of freestalls. We also used data loggers to record lying behavior on a sample of high-producing cows. In these real-world conditions, the variation in air speeds among the stalls, rather than the average, was a key factor. When air speeds differed more between stalls on the same farm, daily lying time also differed more between cows on that farm. This told us that consistency is important.
As summer approaches, consider taking some air speed measurements at cow lying height to check for consistency between locations. Adjustments to the fans or ventilation system setup may be needed to make sure all stalls get air speeds of at least 200 feet per minute. This consistency can help ensure that all cows get adequate rest in warm weather.
