Differences between cats and dogs: a nutritional view.

Cats and dogs have been associated with man for many centuries, and in modern society they probably represent the two most popular companion animals. In 1992 there were approximately forty million cats and thirty-eight million dogs in Europe, representing 18 and 21% of households respectively. Despite their popularity, the nutritional requirements of both species have only been studied in detail during the last 20 years. Regarding zoological classification, both cats and dogs fall into the order Carnivora. However, a comparison of the nutritional requirements of the cat and the dog supports the hypothesis that specialization consistent with the evolutionary influence of a strict carnivorous diet has occurred in the cat. In addition, there appears to be more variety in the diets of Canids than in those of Felids. The ancestors of dogs are known to eat mammals, fish, birds and amphibians as well as vegetable matter (berries, apples, pears) whereas wild cats only eat animals (small antelopes, rodents, birds, fish, etc; Rohrs, 1987). Examples of the cat specializations can be summarized as follows: 1. the cat has limited ability to regulate the catabolic enzymes of amino acid metabolism, which causes the cat to require a higher level of dietary protein for maintenance than the dog; 2. the cat has a lower capacity to synthesize the sulphonic acid taurine than the dog and is unable to conjugate bile acids to glycine. Thus the cat, unlike the dog, cannot meet its taurine requirement from dietary S-containing amino acids; 3. the cat cannot synthesize sufficient nicotinic acid from tryptophan because of an increased activity of a-picolinic acid decarboxylase (EC 4.1.1.45) leading to the endproduct glutamate rather than nicotinic acid; 4. the cat is unable to convert carotene to retinol and, therefore, cannot satisfy its vitamin A requirements with a herbivorous diet alone; 5. the cat cannot convert sufficient linoleic acid to meet its requirement for arachidonic acid; 6. the cat seems to be unable to cope with high levels of carbohydrate in its diet and appears to be in a constant state of gluconeogenesis. These feline specific peculiarities (which will be presented in the present paper) appear to confirm that, unlike the dog, the cat is an obligate carnivore and is dependent on a supply of at least some animal-derived materials in its diet.