Our previous study found that malnutrition significantly enhanced the levels of diamine oxidase, D-lactate, lipopolysaccharide, and histamine in the serum and reduced the expression level of tight junction, indicating an impaired barrier function, thereby decreased the body weight and average daily gain (ADG) of yaks, while Gln supplementation can alleviate them [27]. The gene discussed is AOC1; the disease is malnutrition.