Behavioural Responses of Beef Cattle to Hot Conditions.

Simple Summary: A better understanding of cattle behavioural responses during high environmental temperatures could be beneficial for the diagnosis of heat loads. In the current study, 24 Black Angus steers fed a finisher diet based on cereal grain or a substituted diet (8% of the grain replaced by an isoenergetic amount of lucerne hay) were exposed to hot conditions, and changes in their behavioural and physiological dynamics were assessed. Compared to the recovery period, hot conditions increased respiration rate and were associated with increased stepping behaviour, especially by left limbs. Cattle also increased the orientation of their heads downward, their ears backward, and their tail vertically or raised, and they reduced eating, grooming, and scratching during the heat load period. Changes in head, ear and tail position, breathing changes persisted during the heat load period, suggesting that these behaviours have diagnostic value. Cattle that were fed a diet based on the cereal grain stood for longer and were more likely to hold their ears backward and tail vertically, whereas those on the substituted diet were more likely to display axial ears and hold their head in a neutral position. We conclude that cattle have subtle changes in behaviour in response to hot conditions, which may be of value for diagnostic purposes. Cattle are increasingly exposed to hot temperatures as a result of climate change, and a better understanding of behavioural responses could be beneficial for the diagnosis of heat loads. The changes in the positioning of key body parts, feeding behaviour, body maintenance, and respiratory dynamics were assessed in 24 Black Angus steers individually exposed to hot conditions and fed a finisher diet based on cereal grain or a substituted diet (8% of the grain replaced by an isoenergetic amount of lucerne hay). Increased respiration rate during the heat load period, compared to the recovery period, was associated with increased stepping, especially by left limbs. Cattle also reduced eating, grooming, and scratching during the heat load period. The lowered head, backward ear, vertical or raised tail, and increased respiration rate and panting persisted in cattle during the heat load period. Cattle on the cereal grain diet stood for longer and were more likely to hold their ears backward and tail vertical than those on the substituted diet. We conclude that these behaviours could be used to detect animals that are most affected and that changing from a cereal-based diet to a substituted diet containing a higher amount of fibre, such as lucerne hay, can reduce hyperthermic behavioural responses to a heat load. [ABSTRACT FROM AUTHOR]