Lysine

Lysine is an essential amino acid that dogs and cats cannot make and must obtain from food. It is needed for growth, for building body proteins, for forming collagen and for calcium absorption, and it is often the amino acid used to judge the quality of a protein source. There is a processing pitfall worth knowing: excessive heat can bind lysine to sugars in the Maillard reaction, locking it up and lowering its availability even when the [crude protein](/glossary/crude-protein) figure looks fine, which is why gentle, controlled cooking matters for protein quality. Deficiency slows growth in young animals and degrades tissue quality. The best sources are animal proteins such as meat, fish and egg, while some plant proteins are comparatively low in lysine, another reason animal protein suits these species. Cats give lysine a second, non-nutritional storyline: it was long supplemented in an attempt to limit feline herpesvirus signs, which cause respiratory and eye problems, but recent evidence on this use is conflicting and the benefit is now widely questioned, so it should not be assumed to work and is best discussed with a veterinarian. This therapeutic use is quite separate from lysine's basic dietary role. As one of the [essential amino acids](/glossary/essential-amino-acids), lysine sits alongside [methionine](/glossary/methionine) on premium labels. See the [Petipedia glossary](/glossary).

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General documentary information. For an individual animal, a veterinarian's advice takes precedence over any online content.