Duck

It often is. Duck is a protein most cats have not eaten before, which is why it is a frequent choice for cats with food allergies.

Duck is poultry meat that cat foods use as an alternative to chicken. Cornell Feline Health Center explains that cats are obligate carnivores that rely on nutrients found only in animal products, and duck is one such source. It is slightly higher in fat than chicken. If your cat has a medical condition, needs to lose weight or has a food allergy, ask your veterinarian.

Source: vet.cornell.edu

Duck gives cat food makers a named poultry protein other than chicken. Many cats have never eaten it, so it shows up in recipes built around a less common protein. It adds iron and B vitamins. The label may also list it as roasted duck, which Pettings counts as the same ingredient.

No protein is truly hypoallergenic, duck included. Tufts veterinary nutritionists say that feeding a diet with duck, kangaroo, lamb or venison does not prevent food allergies. It only changes which protein a pet might react to later. The closest thing to a hypoallergenic diet, they explain, is a hydrolyzed diet sold through veterinarians.

Source: sites.tufts.edu

Yes, duck is a little higher in fat than chicken, so it supplies more calories per gram. That can suit active cats with higher energy needs. For a less active or overweight cat, the overall fat and calorie content of the food matters more than any single ingredient. Check the guaranteed analysis and calorie statement on the bag.

Pettings gives duck 5 out of 5 and lists it as a named animal protein. It appears on 6 of the 149 dry cat foods we list, counting labels that say roasted duck. The score covers the ingredient alone. Each food's page shows how the full recipe scores overall.