Feed & Additive Magazine Issue 17 June 2022

ISSUE FOCUS FEED & ADDITIVE MAGAZINE June 2022 29 In dairy cows, the impact of heat stress can be easily measured, in particular through reduced milk production. Although there is less visibility, fattening cattle suffer just as much as dairy cows in warm temperatures. Detecting the signs of heat stress as early as possible is essential to preserving the herd full production and health potential by adjusting its management, with a particular focus on nutrition. HEAT STRESS: A STILL UNDERESTIMATED ISSUE IN BOVINE From 24°C onwards, the animal immediately decreases its feed intake, which then takes several days to stabilize again, even at lower temperatures. The animals increase their respiratory rate and use up energy to dissipate excess heat, which contributes to a significant increase in maintenance needs: this is heat stress. Susceptibility to heat stress also depends on genetic traits: for example, dark coat breeds suffer more than the light coat ones. Fat layer also plays the role of thermal shield, slowing down the dissipation of heat. Finishing cattle are also more impacted due to their smaller body surface area in proportion to their body weight. HOW TO ASSESS HEAT STRESS IN BEEF CATTLE The temperature–humidity index, or THI, is a common indicator of heat stress risk level (Table 1). This means that not only temperature is important but also the air relative humidity level, which exacerbates the effect of temperature. For beef cattle, the heat stress threshold is estimated at 72 (Orange zone in the THI table) (Gatson, et al., 2019). This means that for example, at 50% humidity, cattle suffer from heat stress from 25°C. By placing a thermo-hygrometer — or new generation of sensors that continuously monitor THI within the barn, — close to the animals, producers can monitor and anticipate heat stress risks. The negative impact of heat stress is linked to the THI level and to the duration of exposure, both in terms of the number of hours/day and the number of consecutive days of stress. ANIMAL OBSERVATION IS KEY TO DETECT EARLY SIGNS OF HEAT STRESS The first visible sign of heat stress is a change of feeding behavior: feed intake is reduced and animals show erratic feeding behavior, feeding at the coolest hours of the day. With more severe HEAT STRESS MANAGEMENT: THE IMPORTANCE OF BEEF CATTLE NUTRITION Bruno Martin Ruminant Technical Support Lallemand Animal Nutrition

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