L-lysine Cat Powder provides the amino acids essential for antibody production to promote normal immune system response and help fight infection. 60 Day Supply. Support your cat’s immune system and respiratory health. This easy-to-use powder supplement contains a generous amount of L-lysine, an amino acid essential for the production of antibodies needed for normal immune system response. Beneficial in helping to manage upper respiratory issues such as conjunctivitis, and other symptoms of feline herpes, our veterinarian-formulated Cat L-lysine Powder is manufactured in Vermont, free of corn, artificial flavors and dyes, and has a great chicken liver taste your kitty will love!