Abstract
Theanine is a naturally occurring amino acid, including two forms, D-theanine and L-theanine. L-theanine is the most common nonprotein amino acid and is soluble in water. Theanine can be found in some plants, such as green tea and some mushrooms. Under stress conditions, theanine is proposed to be a naturally effective additive in preventing reactive oxygen species, thus reducing oxidative stress. In addition, as immune booster in animal body, L-theanine can be applied in the diet to help animals improve their performance, especially their immunity during stress conditions. The digestion of L-theanine improves γδ T cell growth and development. Thus, it is considered an essential compound in boosting immune function. Moreover, the immune function of L-theanine is also shown in immune-related organs through increasing their weights. Theanine seems to be widely used in pigs, mice, and humans. However, the study of theanine in poultry species is scarce. Therefore, to fill the knowledge gap regarding the use of theanine in enhancing poultry immunity, this study aims to synthesize all information on the application of theanine in poultry, focusing on its immune-boosting role.

Key words: animal welfare, animal behavior, immunology, theanine