Water, energy and heat balances of sheep exercising in hot conditions

The aim of the project was to improve the understanding of water, energy and heat stresses on livestock grazing out from water sources in semi-arid environments. To do this, water, energy and thermal balances were studied on shorn and unshorn sheep during exercise and rest in thermoneutral and hot conditions. Initially, water and energy turnovers and thermoregulatory responses of animals of various fleece lengths were determined indoors while they exercised on a treadmill. Heat production at rest was virtually constant whereas during exercise it increased 2-3 fold. During exercise, unshorn sheep reached higher rectal temperatures, respiratory frequencies and evaporative heat and water losses than shorn animals. Thermoregulatory responses increased in the heat, but lack of solar radiation made direct applicability to field conditions uncertain. A second laboratory trial studied the effects of drinking saline or fresh water on fluid intake, osmoregulation and thermoregulation. Saline intakes did not impair thermoregulatory responses of animals. Under field conditions, the effects of high-or low-protein food intakes on tritiated water turnover, voluntary water intake, live-weight and grazing patterns were measured in commercial flocks grazing lupin or cereal stubble. The lupin diet may have induced greater water turnover and weight gain, and led to more concentrated grazing around the water point. For undetermined reasons grazing of cereals occurred more at the margins of the paddock. A second set of field measurements examined the effects of exercise and rest, and of long and short fleeces; both exercise and short fleece led to greater water turnover. with cereal grazing again being greatest at a distance from water. Finally, these data were used to calculate probable energy and water balances of sheep grazing semi-arid pastures. The emergent patterns were compared with existing models of grazing (from CSIRO), and of thermal balances (from the University of Nottingham). In moderate environments data were in close agreement, but some large differences under field conditions indicated that mathematical modelling of livestock performance, though useful, needs further development