Energy costs of feeding activities and energy expenditure of grazing sheep

Abstract

The energy costs of standing, of rumination, of eating prepared meals, and of grazing were determined in laboratory experiments by indirect calorimetry. Sheep with body weights ranging from 30 to 110 kg were used. Energy expenditure due to standing amounted to 0.34 ± 0.02 kcal/hr/kg body weight. The energy cost of rumination was 0.24 ± 0.03 kcal/hr/kg. Rate of food intake varied from 60 g dry matter/hr with sheep grazing a poor sward to 800 g/hr with sheep eating hay, but in general this did not affect energy expenditure appreciably. The cost of eating prepared meals of either fresh herbage or hay was 0.54 ± 0.05 kcal/hr/kg body weight. It tended to be greatest when rate of food intake was greatest. Energy expenditure due to grazing was also 0.54 ± 0.05 kcal/hr/kg, irrespective of the type of sward and associated grazing behaviour. It is estimated that muscular work, mainly standing and eating, could account for nearly 40% of the daily energy expenditure of a sheep at maintenance, grazing a poor but level pasture, with drinking water available, and only 10% of that of a caged animal. Such a grazing animal could thus have requirements over 40% greater than those of a caged one. With sheep on hilly pasture or a long way from water, the cost of walking could become a major item.