Domestic ducks can eat chicken layer feed supplemented with brewer's yeast. Adding 5 percent brewer's yeast to chicken feed helps provide ducks with the right amount of niacin to grow properly. Ducks can also eat commercial-quality duck feed if it is available.
Ducks also require an adequate amount of leafy greens. Ducklings can eat greens such as grass, Swiss chard and regular lettuce. As ducklings grow, other foods such as fresh peas, cucumber, corn kernels, tomatoes and watermelon can be added to the diet.
Ducks that are kept in enclosed areas without dirt need grit sprinkled on their food once a week. Ducks that are laying eggs may also need crushed oyster shells. However, non-laying ducks and certain breeds do not need oyster shells.