Habitat Quality in Association with Herd Health in Two Bighorn Sheep (Ovis canadensis canadensis) Populations

Multiple factors have been identified as elements of the respiratory disease complex in Rocky Mountain bighorn sheep (Ovis canadensis canadensis). We hypothesized that differences in health factors and Pasteurellaceae in the upper respiratory tracts could exist between populations of bighorn sheep with and without histories of pneumonic epizootics. We evaluated bighorn sheep in the Big Creek area of Central Idaho which had a history of respiratory disease, and hunter-harvested bighorn sheep from the Montana Spanish Peaks Range which had no history of respiratory disease. Factors evaluated included Pasteurellaceae, indicators of exposure to respiratory viruses, lungworm (Protostongylus spp.) loads, nutritional status and forage nutrient availability. Pasteurellaceae were isolated from both populations; however, significant differences (P < 0.01) in β-hemolysis and cytotoxicity were detected between isolates from the two populations; 64% of isolates cultured from Idaho were β-hemolytic and 38% of those produced >50% cytotoxicity. In contrast, 19% of the isolates from Montana were βhemolytic and none of those produced cytotoxicity >50%. Low serum antibody titers against bovine viral diarrhea, and bovine respiratory syncytial virus were detected in Idaho bighorn sheep following a pneumonic epizootic and in both herds against parainfluenza-3 virus. Low lungworm loads were detected in both herds. Forage nutrient values were similar for the two populations; however, the selenium level present in the Montana forage was significantly higher (P = 0.06) than that detected in the Idaho forage. It is concluded that variances in Pasteurellaceae virulence factors and dietary selenium, important in immune function, may be critical factors to consider when identifying conditions favoring a pneumonic epizootic.