ApplawsTuna Fillet with Mackerel Mousse

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.

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 plant oil added as a source of linoleic acid, the omega-6 fat dogs and cats need for skin and coat. It is cheap, stable and well tolerated. Sunflower oil contains no omega-3, so a food that uses it as the main fat will usually add fish oil or flaxseed for balance. The high-oleic variety is lower in linoleic acid and used mainly for shelf stability.

The familiar white potato, used as a carbohydrate source in many grain-free foods. Potato starch binds kibble; potato protein is a concentrated plant protein that lifts the protein figure on the bag. Cooked potato is safe and well digested. Grain-free foods built on potatoes and legumes were part of the FDA's 2018 to 2022 look at diet-associated heart disease in dogs, which did not establish a cause; the agency has not asked for any to be withdrawn.