OVERWINTER SURVIVAL OF MALLARDS FED SELENIUM

Adult male mallards (Anas platyrhynchos) were fed diets supplemented w ith 0, 10, 20, 40, or 80 mug/g selenium in the form of selenomethionin e. Mortality in each of these treatments was 0, 0, 25, 95, and 100%, r espectively, during a 16-week exposure that started in November. After one week of treatment, body weights were significantly depressed by t he 20, 40, and 80-mug/g selenium treatments, but not by 10 mug/g selen ium. Four weeks after being returned to an untreated diet, the body we ight of birds fed 20 mug/g selenium had increased to the point of bein g statistically inseparable from the weight of controls. Signs of sele nium poisoning in the dead included severe emaciation, mottling of the liver, empty gizzard, and the presence of a yellowish fluid around so me organs. Concentrations of selenium in blood were related to dietary treatments, but mortality was not clearly related to a threshold conc entration of selenium in blood.