Changes in the rate of heat production of calves during grazing and eating

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Abstract
The rates of O2 consumption by young Friesian cattle were measured before, during and after consumption of cut or standing pasture; the animals were restrained in a paddock during these measurements. Mean increases in heat production during eating were 2.38 and 2.80 kJ/h per kg live weight for the eating of cut pasture (dried and fresh) and the grazing of standing pasture, respectively. Mean rates of eating were 1.20, 1.26, and 0.84 kg DM/h for the cut dried, cut fresh and standing pasture, respectively. When expressed per kg DM consumed, mean increases in heat production during eating were 253 and 489 kJ/kg DM consumed for the cut pasture (dried and fresh) and standing pasture, respectively. The rate at which metabolizable energy is ingested is likely to exert a major influence on the overall energy expenditure of an animal. The implications of this to the grazing animal are discussed.