Ingestion of Grit by Bighorn Sheep

During spring and early summer in 1970 grit was found to comprise a considerable percentage of the dry weight of feces in two Alberta bighorn sheep (Ovis canadensis) herds. Similar percentages of fecal grit in domestic sheep in New Zealand have been correlated with high tooth wear, a factor which results in such impaired metabolic performance that premature culling of affected animals becomes necessary. A hypothetical case of ingested grit making a possible contribution to mortality in bighorns is argued. J. WILDL. MANAGE. 38(4):880-883 Tooth wear and ingestion of grit are topics which have occasionally been correlated but about which little seems known in wild ruminants. Even among domestic species, most of the available information refers to Australian and New Zealand sheep. In New Zealand, a country heavily dependent for export earnings on wool, the number of years of economically gainful productivity from each individual sheep is clearly of considerable significance. Excessive tooth wear has for many years been regarded as a factor contributing to a decline in vitality and a variety of causative agents has been suggested. An early inquiry was that of Barnicoat (1957) who suggested that wear was due to the abrasive action of herbage fiber. Working in Australia, Baker et al. (1959) suggested that the very hard opal phytoliths found in certain pasture species might play a part in wear of sheep's teeth, and Barnicoat and Hall (1960) focused attention on the chemical process of proteolysis as a possible cause of wear. Baker et al. (1961) reported the ingestion of grit by sheep but, rather than to tooth wear, related this and certain plant inclusions to abrasion of the gut wall, a feature which they suggested may pave the way for infection. The experimental study of Cutress and Healy (1965), how ver, convincingly demonstrated that plant juices were only of minor significance while in a companion paper Healy and Ludwig (1965) showed that the most significant causative agent in tooth wear was in fact particles of ingested soil. Support for this contention has come from Healy (1967) and from a study undertaken in Ireland by Nolan and Black (1970). Arnold et al. (1966) have observed that high stocking rates, resulting in severe tooth wear, are also accompanied by increases in both wool production and body weight, even many months after the return of the animals to easier conditions. The authors attributed the increases to absorbed silica. Healy et al. (1967) have none the less claimed that "the saving of 0.2 inches of incisors would mean that one or possibly two more breeding seasons could be obtained from ewes." Against this background it was of interest to discover that the amount of grit present in the feces of Canadian bighorn sheep was comparable with the highest levels measured in New Zealand domestic sheep. This study was made possible through the courtesy and facilities made available by the University of Calgary. Especial thanks are due to V. Geist.