Duck has become a very popular ingredient in many cat and dog foods, especially advertised new protein and limited-ingredient diets. For example, duck and rice, duck and potato or sweet potato, and duck and oats used in canned, dry and treat products.
The implication of a limited ingredient diet is that the food avoids a protein that might cause a hypersensitivity or allergic response in the dog or cat, leading to any number of issues, such as skin conditions, diarrhea, and vomiting to name a few.
In theory, limited ingredient diets for pets afflicted with true ingredient hypersensitivities, eliminate the possibility of closely-related species that may cross-react and, therefore, cause an adverse reaction, (e.g. beef with buffalo, chicken with turkey). Duck might cross-react if the pet has a poultry sensitivity, but so far duck has generally been well accepted by dogs and cats.
Reported in Pet Food Industry magazine by Greg Aldrich, PhD