Cats have different dietary needs compared to dogs. Many of the special needs are due to a difference in liver and digestive enzymes
between the two species. The Association of American Feed Control Officials (AAFCO
) has developed separate minimum requirements for dog and cat foods (See Table 1), and from these, it becomes evident why dog food should NOT be fed to cats. Special feline nutritional needs include:
Protein is a source of nitrogen, and cats require a higher protein level than dogs. This may be due to the cat's inability to regulate the rate at which liver enzymes break down protein. If dietary protein is in low quantities or not available, the cat's body will soon start breaking down the protein in its own muscle.
Taurine is an amino acid, which is necessary for proper bile formation, health of the eye, and functioning of the heart muscle. Cats require a high amount of taurine for their body functions, yet have limited enzymes which can produce taurine from other amino acids such as methionine and cysteine. Therefore, they need a diet high in taurine. If taurine is deficient, signs such as a heart condition called dilated cardiomyopathy, retinal degeneration, reproductive failure, and abnormal kitten development can occur.
Arginine is also an amino acid. Most animals manufacture the amino acid ornithine through various processes, some of which require arginine. In cats, the only method to produce ornithine is to convert it from arginine. Ornithine is necessary because it binds ammonia produced from the breakdown of protein. If cats are deficient in arginine, there will not be enough ornithine to bind the ammonia, and severe signs such as salivation, vocalization, ataxia, and even death can result from the high ammonia levels. These signs often occur several hours after a meal, when most of the ammonia is produced. Although deficiencies are rare, they cat occur in cats who are not eating or have certain liver diseases such as hepatic lipidosis.
Arachidonic acid is one of the essential fatty acids. Dogs can manufacture arachidonic acid from linoleic acid or gamma-linolenic acid. Cats can not. Arachidonic acid is necessary to produce an inflammatory response. In many cases, such as in allergies, the goal is to suppress the inflammatory response. But in other cases, the response is a necessary means by which the body can protect itself. Arachidonic acid also helps to regulate skin growth, and is necessary for proper blood clotting, and the functioning of the reproductive and gastrointestinal systems. Arachidonic acid is found in animal fats which must therefore be included as part of the diet. Like dogs, cats also require linoleic acid, another fatty acid.
Active form of Vitamin A
Cats lack the enzyme which can convert beta-carotene to retinol, the active form of Vitamin A. Therefore, they require a preformed Vitamin A, which is present only in foods of animal origin, and is usually included in cat foods as retinyl palmitate. Deficiencies of Vitamin A are rare, but signs include night blindness, retarded growth, and poor quality skin and hair coat.
Many animals can synthesize niacin, a B vitamin, from the amino acid tryptophan. Cats can not manufacture it in sufficient quantities, thus require higher amounts in their diet. Deficiencies in niacin can lead to loss of appetite and weight, inflamed gums, and hemorrhagic diarrhea.
Cats have less need for starch, and a decreased ability to digest it. Dogs need, and can tolerate, higher starch levels in their diet than cats.
Table 1. Differences between AAFCO cat and dog food nutrient profiles