ISSUE FOCUS 48 FEED & ADDITIVE MAGAZINE July 2025 THERMAL STRESS IN COWS: UNDERSTANDING THE METABOLIC BURDEN Dr. Melinda Culver Veterinarian Biochem Thermal stress in cows disrupts the delicate balance between heat production and dissipation, leading to a cascade of physiological effects that impact digestion, immunity, and reproduction. While cows are efficient feed-to-food converters, their limited ability to sweat makes them vulnerable in hot, humid conditions. As climate challenges rise, innovative solutions are being explored to safeguard performance and welfare—especially outside the thermoneutral zone. Cows have superpowers. Humans and cows share a long history, with humans relying on these animals for a stable food source. The symbiotic relationship between cows and their ruminal microorganisms is crucial to produce highly nutritious food from poor-quality feed— using plants, stems, and by-products that are unsuitable for other production animals. Consequently, they play a substantial role as a valuable source of food. A 4-LEGGED HEATING POWER STATION The cow is a so-called homeothermic animal. That is, they can maintain their body temperature through metabolic activity. With a constantly active metabolism, cows are excellent feed-to-food converters. However, these superpowers come at a cost; they generate an incredible amount of heat. In an adult cow, this can be almost 1.2 kWh of heat, enough to theoretically heat a small house with the excess heat from three cows. A fact that has been exploited by farmers for centuries. A cow’s metabolism is a complex interplay of microbial activity and physiological efficiency, which generates heat from basal metabolism, activity, digestion, and production. Basal metabolic heat comes from basic cell functions that keep the body alive. It also comes from muscle activity, and from the heat produced by other bodily processes that help with growth, lactation, pregnancy, and the production of proteins or fats. The digestion of feedstuffs also releases heat. At the center of digestion is the rumen—a large-volume anaerobic bioreactor system containing billions of bacteria, protozoa, and fungi—and much of the heat generated is from the intense microbial activity here (Figure 1). Ruminal fermentation generates enough heat to raise the rumen temperature to about 1° C higher than the core body temperature of 38 – 39° C. These microorganisms in the rumen break down carbohydrates from the diet fermentation into volatile fatty acids (VFAs) such as acetate, propionate, and
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