The seasonal nutritional physiology of polar bears (Ursus maritimus) under human care

Despite the seasonal ecology of polar bears, zoos feed their captive bears a high-protein, high-calorie diet year-round. This approach to polar bear husbandry has been associated with poor welfare and death by liver/kidney disease. I assessed the effects of diet – calories and macronutrients – on the physiology and behaviour of 5 bears at The Toronto Zoo. Diet varied seasonally in caloric intake, and bears were fed a high-protein diet from January 2018 to February 2019, and a high-fat diet from January 2022 to June 2023. During both periods, the body mass and fat, blood chemistry, and body temperature of bears were recorded. Behavior was observed under the high-fat diet. Diet had significant effects on body and blood variables. Calories had significant effects on activity and body temperature, while macronutrients had no effect on these variables, suggesting thermal stress and laziness are not relevant welfare concerns for captive bears on this diet.