Do cats need vitamin supplements? Blog napfcheck L Carnitine for dogs and cats L carnitine is primarily synthesized in the liver from the amino acids lysine and methionine through a series of four enzymatic reactions, with the liver and kidneys converting the precursor butyrobetaine into active Dietary l Carnitine Supplementation in Obese Cats Alters Carnitine Metabolism and Decreases Ketosis during Fasting and Induced Hepatic Lipidosis ScienceDirect