摘要Domestic cats and dogs are carnivores that have evolved differentially in the nutrition and metabolism of amino acids.This article highlights both proteinogenic and nonproteinogenic amino acids.Dogs inadequately synthesize citrul-line(the precursor of arginine)from glutamine,glutamate,and proline in the small intestine.Although most breeds of dogs have potential for adequately converting cysteine into taurine in the liver,a small proportion(1.3％-2.5％)of the Newfoundland dogs fed commercially available balanced diets exhibit a deficiency of taurine possibly due to gene mutations.Certain breeds of dogs(e.g.,golden retrievers)are more prone to taurine deficiency possibly due to lower hepatic activities of cysteine dioxygenase and cysteine sulfinate decarboxylase.De novo synthesis of arginine and taurine is very limited in cats.Thus,concentrations of both taurine and arginine in feline milk are the greatest among domestic mammals.Compared with dogs,cats have greater endogenous nitrogen losses and higher dietary requirements for many amino acids(e.g.,arginine,taurine,cysteine,and tyrosine),and are less sensitive to amino acid imbalances and antagonisms.Throughout adulthood,cats and dogs may lose 34％and 21％of their lean body mass,respectively.Adequate intakes of high-quality protein(i.e.,32％and 40％animal protein in diets of aging dogs and cats,respectively;dry matter basis)are recommended to alleviate aging-associated reductions in the mass and func-tion of skeletal muscles and bones.Pet-food grade animal-sourced foodstuffs are excellent sources of both proteino-genic amino acids and taurine for cats and dogs,and can help to optimize their growth,development,and health.