ISSUE FOCUS 26 FEED & ADDITIVE MAGAZINE July 2025 FEED FORMULATION STRATEGIES TO COMBAT HEAT STRESS IN LACTATING COWS Aurélien Piron Ruminant Technical Manager Lallemand Animal Nutrition Feed formulation strategies play a critical role in mitigating heat stress in transition dairy cows, as demonstrated by an August 2023 trial in the Czech Republic where the temperature-humidity index (THI) reached 82. During this period of severe heat, researchers evaluated the effects of a targeted nutritional approach including rumen-specific live yeast, antioxidants rich in enzyme superoxide dismutase (SOD), and organic selenium supplementation. While all cows experienced a drop in milk yield, those receiving the supplement showed significantly less severe declines. This research highlight how nutritional solutions can support resilience, particularly around calving during heat stress events. On August 8, 2023, the temperature-humidity index (THI) in Tatenice, Czech Republic, reached 82 -- well into the severe heat stress range for dairy cattle. For the next two weeks, this elevated THI would test every cow in the 500-head herd. While some cows suffered milk losses of nearly 7 kilograms per day, others maintained their production with losses of less than 4 kilograms daily. The difference wasn't management, genetics or cooling systems; it was a targeted nutritional intervention based on understanding heat stress as a multi-system biological challenge. THE HEAT STRESS CHALLENGE Heat stress begins affecting lactating dairy cows at 21°C. What’s more is that production losses start at just 18°C. The THI combines both factors to reflect what animals actually experience — as humidity rises, even constant temperatures become more stressful because the body's cooling mechanisms become less effective. Once THI values exceed 72, production losses become inevitable. Dairy operations face these conditions with increasing frequency, making heat stress management a €120 annual direct loss cost per cow in milking herds.1,2 These periods lead to reduced feed intake and more standing time, resulting in less milk and poorer-quality milk.3,4 Plus, there are long-term side effects of heat stress that aren’t revealed until years later, including diminished mammary gland tissue development and poor calf health in offspring of heat-stressed cows.5,6 The wide-ranging effects of heat stress on dairy cows indicate this challenge involves multiple systems within the animal.
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