Globulin proteins play a critical role in protecting against infection. Trained Alaskan sled dogs have low blood globulin concentrations at rest with a further decline in blood globulins during long distance exercise. The cause and prevalence of this phenomenon and the specific globulin fractions affected (immunoglobulins A, E, G, and M) are currently unknown. To determine the prevalence and severity of depressed blood globulin concentrations in trained Alaskan sled dogs prior to and following a long distance endurance race, and to determine the specific immunoglobulin fractions affected, venous blood samples will be collected from 100 randomly selected Alaskan sled dogs that successfully complete the Iditarod Trail Race. Samples will be retrospectively matched with each dogs pre-race blood sample and all samples will be analyzed for total globulin concentration and immunoglobulin A, E, G and M concentrations. The information derived from this study may aid further investigations into possible causes of low serum globulin concentrations in racing sled dogs, and the potential impact of low blood globulin concentrations on sled dog health.