|Cat eating rat - plenty of arginine - Photo by aj_1328|
Arginine is an amino acid. Most species of adult animals synthesize arginine. "Synthesize" refers to a chemical reaction in which arginine is made. However cats and dogs have a limited capacity to synthesize it. It needs therefore to be in the diet as a dietary supplement. It is a "dietary essential"¹.
The metabolism of a high protein diet results in large amounts of ammonia being generated which has to be eliminated by conversion to urea for excretion from the body in urine. Arginine is essential in this process.
A lack of arginine causes an immediate and severe problem. Cats develop severe hyperammonemia "within several hours of consuming a single arginine-free meal" ¹ ("hyperammonemia" is excess ammonia in the blood).
Symptoms include: vomiting, muscular spasms, ataxia (lack of coordination), hyperesthesia, tetanic spasms, leading to coma and death. This indicates the importance of arginine. It is a hidden importance as this nutrient is almost always included in the cat's diet because it is present in nearly all protein sources.
Note: (1) The Cat It's Behavior, Nutrition & Health page 305 ISBN 978-0-8138-0331-9