Restrictive amino acids refer to essential amino acids that cannot meet the needs of animals in feed or diet. Their shortage limits the utilization of other amino acids in feed or diet, thus reducing the nutritional value of the whole feed or diet protein. Generally, the most serious one is the first restrictive amino acid, which is correspondingly the second, third and fourth restrictive amino acids.

According to the comparison between the analysis results of feed amino acids and the requirements of animals, it can be inferred which essential amino acids in feed are restricted amino acids. The more the difference between the supply and requirements of essential amino acids, the greater the degree of deficiency and the stronger the restrictive effect.

Lysine is the first restrictive amino acid of chicken in cereal feed. In most corn-bean cake diets, methionine and lysine are the first restrictive amino acids for poultry.