Effects of ambient temperature and head cooling on energy expenditure, food intake and heat tolerance of Brahman and Brahman × Friesian cattle working on treadmills

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Abstract
Energy expenditure, food intake and some physiological reactions of Brahman and Brahman × British Friesian cattle working on an inclined treadmill at 33°C were studied. The effect of work at a lower ambient temperature (15°C) and local cooling of the head region while at 33°C were also investigated. Whilst walking up a 6° gradient at 1 m/s, animals expended about four times as much energy as when standing. Heat production during work (W/kgM0·75) was similar in both breeds and was not influenced by the treatments imposed. Crossbred animals showed significantly higher respiration rates and sweating rates than the Brahmans immediately after working for 30 min at 33°C. Food intake and body-weight changes in the crossbreds at 33°C compared with Brahmans provided further evidence that these animals were less tolerant of the conditions. Head cooling during work appeared to reduce depression in food intake associated with work at 33°C in both breeds although it had no effect on physiological changes.