Proteins are complex molecules made up of amino acids, the building blocks of cell growth, maintenance and repair. In companion animals, one of the biggest demands for protein comes from the maintenance of fur and hair, which can use up to 30 percent of the daily protein intake, according to Barbara Fougère, BVSc.
Proteins are made up of 20 amino acids. While dogs, cats and even humans produce about half of these amino acids internally, the other half, termed “essential amino acids,” need to be provided by the diet. The 10 essential amino acids are arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. If even one of these “essentials” is deficient, as Lowell Ackerman, DVM, explains, the body cannot make specific proteins effectively. Amino acids work in a step-by-step fashion to manufacture protein.
If one of the steps is missing, the process stops. The biological value of proteins indicates how efficiently an animal utilizes them. Animal nutrition expert Donald Strombeck, DVM, notes that this value is high for proteins from meat, most meat by-products, eggs and dairy products. “Dogs digest these proteins efficiently and they provide amino acids in proportions suitable for tissue protein synthesis. In contrast, the biological value of most plant proteins is low, due to insufficiencies of specific amino acids and lower digestibility.”