ISSUE FOCUS FEED & ADDITIVE MAGAZINE July 2022 43 About Geoffrey Dahl Geoffrey Dahl, Harriet B. Weeks Professor, President, American Dairy Science Association. Dr. Dahl conducts applied and basic research with direct impact on animal production and health. Specifically, his program focuses on understanding the physiological impact of management interventions, notably photoperiod and heat stress abatement, at various stages of the lactation cycle, in an attempt to harness that knowledge to optimize cow health and performance. The fundamental aspects of Geoff ’s research have led to application in other agriculturally important species, including sheep, goats and pigs. About Glenn Holub Dr. Glenn Holub, Executive Dairy Technology Manager with Phibro Animal Health, was raised on a small dairy farm on the Texas gulf coast. He received his B.S., M. Ag, and PhD from Texas A&M University in Animal and Dairy Science. He served as a county agent for 12 years, as lecturer and faculty manager of the A&M Dairy Cattle Center for five years, feed company nutritionist and quality control with Land O’ Lakes/Purina and Gores, Inc. for five years, and professor of Animal Science at Texas A&M University for eight years before joining Phibro Animal Health over eight years ago. Each and every one of these positions over 36 years of his career has developed his thought process and ideals of the dairy industry from various points of view. that were heat stressed and fed OmniGen during the dry period performed better once they freshened than those that were heat stressed and not fed OmniGen during the dry period. That suggests there is some benefit to feeding OmniGen. We also saw a reduction in respiration rates and rectal temperatures - which was similar to research responses done with heat stress cows - in the cows fed OmniGen. What factors determine how a cow recovers from heat stress? The severity and duration of the heat stress and the stage of lactation affect how a cow responds to and recovers from heat stress. Based on our data, it seems like cows that are further along in lactation may be more profoundly affected long-term from heat stress than animals that are early in lactation. And certainly, cows that are dry are going to be profoundly impacted by heat stress. So, it’s really a combination of how severe that heat stress is, how long it persisted, and what physiologic stage the animal is in. All these factors determine how much of a recovery the animal will be able to make, if any, from heat stress. What surprises people the most about heat stress? People are always surprised how much time of the year, and where, heat stress poses an issue. Really the only state where you don’t have to worry about heat stress is Alaska, but there obviously aren’t a lot of cows there either. Places that always tend to surprise people are the upper Midwest or the Northeast in terms of how much time of the year they experience heat stress. On average, across the top dairy states in the U.S., we’ve got about three months of heat stress each year, defined by an average THI for the day being greater than 68. This means that for at least a quarter of the year, animals are potentially heat stressed. And it’s not just in southern states like Florida or Arizona. There’s also significant potential impact of dry period heat stress in places like Indiana, Pennsylvania and even Michigan and Wisconsin. That’s a lot of unrecognized heat stress. 1. Key et al., 2014. Climate Change, Heat stress and U.S. Dairy Production, Rep. No. 175.
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