ISSUE FOCUS 40 FEED & ADDITIVE MAGAZINE July 2022 As the Harriet B. Weeks professor in the Department of Animal Sciences, University of Florida, Dr. Geoffrey Dahl has led numerous studies examining the effects of heat stress on dairy cows at all phases of production. He recently teamed up with Dr. Glenn Holub, Executive Dairy Technology Manager, at Phibro Animal Health Corporation to host a free webinar titled Milking Us Dry: Dairy’s Most Profit-Draining Challenges – Heat Stress, now available on demand from Phibro Academy. Dr. Dahl answered some common questions about dairy cattle heat stress. What should producers look for as potential early signs of heat stress? The first sign of heat stress is typically that lactating cows, and all cows, are going to have decreased dry matter intake. We know how important DMI is to maintaining milk yield - when DMI decreases, so does milk yield. What’s interesting, though, is that the reduction in milk yield is really beyond what we might expect based on decreased DMI. What’s happening is those cows must use additional energy to get rid of that extra heat — so that’s energy that is not available for milk production purposes. How significantly can heat stress affect milk yield, according to your research? We conducted a study that consistently showed the effects of heat stress on a cow’s next lactation compared to the milk production of cows that were cooled when they were dry or cows that were heat stressed when they were dry. This and other studies indicated we are looking at about an 8 to 10 lb per day reduction in milk yield if cows are heat stressed STOP HEAT STRESS FROM MILKING YOUR PROFITS DRY "Rumen fermentation and lactation require high metabolic heat production, making dairy cows particularly sensitive to heat stress whenever the temperature humidity index (THI) exceeds 68. Heat stress can affect cows’ milk production, reproduction and health, and it costs the average U.S. dairy farmer an average of $264 per cow1 per year. It’s no wonder that heat stress is a popular research topic." Dr. Glenn Holub Executive Dairy Technology Manager Phibro Animal Health Corporation Dr. Geoffrey Dahl Harriet B. Weeks Professor Department of Animal Sciences, University of Florida
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