Effects of cadmium ingestion and food restriction on energy metabolism and tissue metal concentrations in mallard ducks (Anas platyrhynchos).

The single and combined effects of cadmium ingestion and food restriction were examined in a 42-day experiment with male, juvenile mallard ducks. A 2 X 3 factorial design was employed consisting of two levels of food supply (ad libitum and 55% of ad libitum intake) and three levels of cadmium in the food (0, 5, or 50 micrograms Cd/g food). Cadmium ingestion alone had no effect on body or tissue weights, liver glycogen, plasma concentrations of glucose, urea, uric acid, nonesterified fatty acids (NEFA), triiodothyronine (T3), thyroxine (T4), or plasma or adrenal concentrations of corticosterone. The food restriction resulted in reduced body weights and reduced weights of livers, kidneys, and testes, increased adrenal weights, reduced liver glycogen, increased plasma NEFA concentrations, reduced plasma T3 and T4 concentrations, and increased adrenal corticosterone concentrations. In combination with the food restriction, cadmium ingestion further reduced plasma T3 concentrations and a similar trend was noted for T4. Additionally, the highest plasma NEFA concentrations and highest plasma and adrenal concentrations of corticosterone were observed in food-restricted ducks receiving the highest level of dietary cadmium. These results suggest the ability of cadmium ingestion to enhance food restriction-induced alterations in energy metabolism at levels of dietary cadmium that are by themselves without apparent effect. Also, cadmium ingestion resulted in increased kidney concentrations of copper and zinc; this effect on kidney zinc concentrations was increased in food-restricted ducks.