2-Hydroxy-4-(methylthio)butanoic acid (HMTBA), with CAS number 583-91-5, is a white to off-white crystalline powder. It is a methionine hydroxy analogue, a key organic acid widely used in animal nutrition. Its primary function is as a source of methionine, an essential sulfur-containing amino acid, for livestock and poultry. The main application of HMTBA is as a feed additive to supplement methionine in the diets of monogastric animals such as poultry, swine, and aquaculture species. It is efficiently absorbed and metabolized in the animal's body to provide bioavailable methionine, which is crucial for protein synthesis, feather and hair growth, and overall metabolic functions. Compared to DL-methionine, HMTBA offers advantages in certain physiological conditions and is a vital component in formulating balanced, cost-effective animal feeds to support optimal growth and health. Beyond animal feed, HMTBA also finds use as a nutritional supplement and a precursor in the synthesis of other compounds. It is recognized for its stability and handling characteristics in feed manufacturing processes.