methionine is always classified as the first limiting amino acid in poultry. Methionine has many physiological functions, e.g. as an important methyl donor to provide the methyl group (CH4) necessary for metabolism in the body. Methionine is also known to reduce oxidative stress in the body by increasing antioxidative compounds such as glutathione. Methionine not only serves as a constituent of body protein but also is involved in the development of the digestive tract and growth performance. Furthermore, it has a function of increasing muscle mass, feather development and improving egg production in poultry.