amino acid is the basic unit of protein, which is composed of carbon, hydrogen, oxygen, sulfur and other elements. It is an amino-containing organic acid. Protein in the feed is decomposed into amino acids by protease in the gastrointestinal tract, enters the blood circulation, participates in the metabolism process in vivo, and synthesizes chicken protein.

There are more than 2 kinds of amino acids that make up protein, which can be divided into two categories: essential amino acids and non-essential amino acids. Essential amino acids refer to amino acids that cannot be synthesized or synthesized slowly in chickens and cannot meet the needs of chicken growth and development, and must be supplied by feed. There are 11 kinds of essential amino acids in chicken, namely methionine, lysine, arginine, threonine, isoleucine, leucine, tryptophan, phenylalanine, histidine, valine and glycine. Although cystine can be synthesized from methionine and tyrosine can be synthesized from phenylalanine in chickens, it means that when cystine and tyrosine are insufficient in the diet, the requirements of methionine and phenylalanine in the diet are increased. Therefore, cystine and phenylalanine in broiler diets are also called semi-essential amino acids. Non-essential amino acids in chicken refer to amino acids that can be synthesized in chicken, such as serine, alanine and proline.

In the practice of raising chickens, methionine, lysine, arginine, threonine and isoleucine are often not up to the standard of nutritional requirements when mixed with common grass seeds and oil cakes, and their lack will affect the utilization rate of other amino acids, so these amino acids are also called restricted amino acids.

protein itself is like a wooden barrel, and amino acids are every plank that makes up the wooden barrel. Chickens' utilization of protein in feed is like water in the wooden barrel. If the planks (amino acids) that make up the wooden barrel are all the same height, they can be filled with water. If one or two boards are only 7% as tall as other boards, then this barrel can only hold 7% of its water (7 barrels), and the higher boards (extra amino acids) will not work. Therefore, the demand of chickens for protein should be both quantitative and qualitative. That is to say, the requirement of protein in chicken diet should first consider whether the essential amino acids can fully meet the nutritional needs. When all the essential amino acids in the diet meet or exceed the requirements, the protein can be considered as meeting the needs. So, how can we meet the needs of chickens for amino acids? This requires that a variety of protein feeds should be used in the diet, so that the amino acids in the protein of each feed can complement each other. For example, the content of lysine and tryptophan in corn is less than that in bean cake, while the essential amino acids in various animal feeds are relatively perfect. If corn, broken rice, wheat, wheat bran, bean cake, fish meal, silkworm chrysalis and other feeds are mixed into chicken's diet, the amino acids in the diet may tend to be balanced, which is conducive to improving feed reward and chicken's production performance.