An essential amino acid, added when the proteins in a food fall short of the required level. Meat is rich in lysine, so it is usually added when a recipe leans on plant protein, which is lower, or to replace lysine lost in cooking. In cats, lysine supplements were long given for herpesvirus flare-ups, but controlled studies found no benefit and some suggestion of harm at high doses; the small amounts in a complete food are there for nutrition and sit far below those doses.
How it appears on labels
You may see it listed as l- lysine, lysine, l-lysine monohydrochloride.
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Sources
- Merck Veterinary Manual, nutritional requirements of dogs and cats
- Bol and Bunnik, BMC Veterinary Research 2015, lysine supplementation in cats
