The endogenous amino acid excretion is a key index on measurement of true digestibility of amino acid in feedstuffs, and isotope labeled endogenous nitrogen method is one of the effective methods on measurement of the endogenous amino acid excretion. 内源氨基酸排泄量(LEAA)是测定饲料氨基酸真消化率的重要指标,而同位素标记内源氮法是直接测定内源氨基酸排泄量的有效方法之一。