Studies on water and salt metabolism in sheep and goats

Abstract

Taxonomically, sheep and goats are closely related and some varieties are difficult to distinguish. They are widely distributed in the world, and thrive in a variety of climates. In Australia, for example, most of them live in the arid and semi-arid areas (Squires, 1979; Harrington, 1982) where availability of preferred food and fresh water are frequently limited. In these areas, salt bush (Atriplex sp.) and blue bush (Kochia sp.) can constitute the main food sources (Wilson, 1966a), and bore water supplied may also contain a significant level of sodium chloride (Pierce, 1957). In the Galapagos Islands, there have been many sightings of goats on beaches apparently drinking from the sea (Dunson, 1970). Numerous studies on comparisons between sheep and goats in aspects of nutrition and digestion (Jones, Larsen, Javed, Donefer and Grudreau, 1972; Maloiy, Taylor and Clements, 1978; Alam, Poppi and Sykes, 1985; Quick and Dehority, 1986; Dominique, Dellow and Berry, 1991), and water metabolism (Maloiy and Taylor, 1971; MacFarlane and Howard, 1974; Ghosh, Singh, Verma, Saxena and Ranjhan, 1980; Aganga, Umunna, Oyedipe and Okoh, 1989) have been reported. Most of the results indicated that goats have greater efficiency than sheep in digesting a low quality roughage diet, and in using the limited water. Concerning salt loading, however, investigations comparing sheep and goats carried out up to now are scarce and incomplete, being largely part of the nutritional experiments listed above. The wealth of information available is only for the sheep. ... In view of the somewhat restricted information available on comparisons between sheep and goats in their water and salt metabolism, the studies reported in this thesis were designed to investigate the effects of several factors on water and sodium dynamics. These factors included method of salt presentation, animal species and roughage diets, level of salt loads and thermal load.