Effects of Thermal Stress, Breed and Stress Susceptibility on Corticosteroid Binding Globulin in Swine

Day-to-day variations in binding capacity and association constant of corticosteroid binding globulin (CBG) and plasma Cortisol levels were determined in crossbred gilts maintained under controlled or fluctuating environmental temperature and humidity regimes. In addition, effect of breed and stress susceptibility of swine on CBG properties and plasma Cortisol concentrations were also studied. Results of these studies indicated that the binding capacity and association constant of CBG in swine plasma did not vary significantly among samples of plasma collected on subsequent days. Exposure of gilts to a high environmental temperature-high relative humidity stress did not affect the CBG binding properties or plasma Cortisol level. Binding capacity of CBG and plasma Cortisol concentration varied significantly between breeds and herds tested, but the variation was not related to their stress susceptibility status. No differences in binding capacity, association constant or plasma Cortisol level were found between littermate pigs which were either negative or positive to the halothane screening test for stress susceptibility. It was concluded that breeds or strains of swine may differ in CBG activity independently of their stress susceptibility status.