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ToDay's VeTeriNary PracTice | November/December 2015 | tvpjournal.com acVN NuTriTioN NoTes Peer reviewed 70 humans, dogs, and cats need 9, 10, and 11 essential amino acids in the diet, respectively (Table 1). 2 Nonessential amino acids in crude protein can provide nitrogen sources for biosynthetic pathways. Limiting amino acids are those amino acids present in a food in the lowest amounts with regard to what the animal requires. These amino acids can adversely affect effciency of protein utilization and the amount of protein synthesis that occurs. 2 in pet foods, methionine and lysine are often the limiting amino acids. Excess amino acids can be used for fuel and are divided into glucogenic and ketogenic amino acids depending on whether they can be used to produce glucose or acetyl coenzyme a, respectively. in many pet foods, especially those with lower protein content, taurine is added, but it is only essential in cats because, in dogs, enzymatic conversion of cysteine to taurine is more active. Defciency most notably causes dilated cardiomyopathy in dogs and cats and central retinal degeneration in cats. 3 While some species reduce food intake when fed an amino-acid defcient diet, cats are a notable TAble 1. essential & selected nonessential Amino Acids for Dogs & Cats Amino A CiD sele CteD FUnCtions & rePorteD tHerAPeUtiC BeneFits Essential Amino Acids Branched Chain Valine (Val) Leucine (Leu) Isoleucine (Ile) • Common constituents of proteins • Leucine supplementation may enhance lean body mass and prevent muscle catabolism Arginine (Arg) • Stimulator and intermediate of urea cycle, preventing hyperammonemia • Nitric oxide precursor • Supplemented for immune function, cancer, and critical illness Histidine (His) • High in hemoglobin • Precursor to histamine Lysine (Lys) • Precursor to carnitine • Limiting in cooked cereal grains • Lysine and carnitine may be helpful for weight loss • Conficting studies on benefts in cats with herpesvirus Methionine (Met) • Limiting in many pet foods • Hair and glutathione synthesis • Methyl donor • Translation (tRNA decodes mRNA sequences into proteins) • Taurine precursor (dogs) Phenylalanine (Phe) • Thyroid hormones • Catecholamines • Melanin Tryptophan (Trp) • Serotonin and melatonin precursor • Niacin (Vitamin B 3 precursor, dogs) Threonine (Thr) • Provides the site for phosphorylation of many enzymes • Modulates neurotransmitter balance in the brain Cats Taurine (Tau) • Constituent of bile • Positive inotrope • Supplemented in nutritional and nonnutritional dilated cardiomyopathy Selected Nonessential Amino Acids Glutamine (Gln) • Most abundant free amino acid • Nitrogen store in muscle • Primary fuel of enterocyte • Supplemented to stabilize gastrointestinal barrier and combat cachexia Asparagine (Asn) • Uncommonly supplemented • Essential for some cancer cells • Drug target of L-asparaginase, which converts to aspartic acid