DL-Methionine

Methionine is an essential amino acid: pets can’t make it, and they use it to build protein and to make other sulfur compounds, including taurine in dogs. Plant proteins such as peas are low in it, so foods that rely on them often add it to balance the protein.

DL-methionine is the form made for this purpose. It also makes urine slightly more acidic, so it’s sometimes part of foods formulated for urinary health. AAFCO lists it among the amino acid additives seen on labels.