EFFECTS OF ACUTE THERMAL-STRESS ON THE IMMUNE-SYSTEM OF THE NORTHERN BOBWHITE (COLINUS-VIRGINIANUS)

We tested the hypothesis that exposure of Northern Bobwhites (Colinus virgi nianus) to acute temperature stressors impairs their immune-syst em function and resistance to disease. Birds were randomly assigned to either a thermoneutral (constant 21 degrees C), cold-stress (cycled f rom 3.6 to -20 degrees C over 24 h), or heat-stress (cycled from 30.8 to 39.0 degrees C over 24 h) treatment for four consecutive days. Immu nocompetence of each bird was evaluated on day 5 using a panel of assa ys, including a measure of resistance to a Pasteurella multocida Type 3 challenge. Neither thermal stressor had an influence on spleen mass or measures of cell-mediated and humoral immunity. Disease resistance of Northern Bobwhites to P. multocida was not influenced by heat stres s but increased following cold stress. Cold stress may have increased the activity of phagocytic leukocytes, which are important in resistan ce of birds to bacterial pathogens. A concomitant decrease in lymphocy te numbers suggested that resistance to viral pathogens was compromise d during cold stress.