Tiki PetsDuck

A poultry protein, fattier and richer in iron than chicken. As with other fresh meats, the wet weight pushes it up the list; duck meal is the dried form. Duck is a different family of bird from chicken and turkey, which is why it is used as a novel protein, though pets that react to chicken sometimes react to duck as well.

The most common protein in pet food, and for dogs one of the most common food allergens, with beef and dairy. If chicken is what your pet reacts to, it hides everywhere: chicken fat, chicken broth, chicken meal, natural flavor. On a label, chicken listed first is weighed with its water still in, so a food leading with fresh chicken often has less chicken protein than one leading with chicken meal. Neither is better; they are different measures.

A complete, highly digestible protein, which is why formulators like it. It is also a documented allergen in about 4% of dogs with food reactions. Egg allergy does not implicate chicken meat; the proteins are different. Dried egg product is the same thing with the water removed. A good ingredient for most pets and a fine-print one for the allergic few.

A fish used mostly in cat foods, where its strong flavor is the point. Tuna is a good protein and a source of omega-3 fats. Two cautions apply to tuna fed often: it is higher in mercury than smaller fish, and cats can become fixated on it and refuse other foods. Both cautions apply to the cat eating tuna every day, and much less to tuna as one ingredient in a complete food fed in rotation.

Fish with no species stated. The maker may use whatever is available, so the fish can change between batches. Nutritionally it is a fine protein and often a source of omega-3 fats. The gap is for pets with a known fish allergy, or whose owners are trying to track which protein causes a reaction, because an unnamed ingredient makes that very hard. Named fish such as salmon or whitefish give you that information.