Characteristics of Nutrition and Metabolism in Dogs and Cats

Domestic dogsand cats have evolved differentially in some aspects of nutrition, metabolism, chemical sensing, and feedingbehavior. The dogs have adapted to omnivorous dietscontaining taurine-abundant meat and starch-rich plant ingredients. By contrast, domestic catsmust consumeanimal-sourced foodsfor survival, growth, and development. Both dogsand catssynthesize vitamin C and many amino acids (AAs, such as alanine, asparagine, aspartate, glutamate, glutamine, glycine, proline, and serine), but have a limited ability to form de novo arginineand vitamin D3. Compared with dogs, cats have greater endogenousnitrogen losses and higher dietary requirements for AAs (particularly arginine, taurine, and tyrosine), B-complex vitamins (niacin, thiamin, folate, and biotin), and choline; exhibit greater rates of gluconeogenesis; are less sensitive to AA imbalances and antagonism; are more capable of concentrating urine through renal reabsorption of water; and cannot tolerate high levels of dietary starch due to limited pancreatic α-amylase activity. In addition, dogs can form sufficient taurinefrom cysteine(for most breeds); arachidonic acidfrom linoleic acid; eicosapentaenoic acid and docosahexaenoic acid from α-linolenic acid; all-trans-retinol from β-carotene; and niacinfrom tryptophan. These synthetic pathways, however, are either absent or limited in all cats due to (a) no or low activities of key enzymes (including pyrroline-5-carboxylate synthase, cysteinedioxygenase, ∆6-desaturase, β-carotene dioxygenase, and quinolinate phosphoribosyltransferase) and (b) diversion of intermediates to other metabolic pathways. Dogs can thrive on one large meal daily, select high-fat over low-fat diets, and consume sweet substances. By contrast, cats eat more frequently during light and dark periods, select high-protein over low-protein diets, refuse dryfood, enjoy a consistent diet, and cannot taste sweetness. This knowledge guides the feeding and care of dogsand cats, as well as the manufacturing of their foods. As abundant sources of essentialnutrients, animal-derivedfoodstuffs play important roles in optimizing the growth, development, and health of the companionanimals.