Chicken Protein Nutrition and the Rational Application of Protein Feed

Protein is one of the most important nutrients for poultry and the material basis of life. It is an important component of the body, participates in the vast majority of biochemical reactions vital to life, and plays an important role in the life activities of animals. The building blocks of protein are amino acids. Feed protein is composed of 22 amino acids, and amino acids form protein molecules of different shapes through different arrangements and combinations. According to whether they can be synthesized in the chicken's body or the speed at which they are synthesized, amino acids can be divided into two major categories: one is essential amino acids, and the other is non-essential amino acids. The essential amino acids for chickens include 13 kinds, among which methionine, lysine, threonine, tryptophan, and isoleucine are present in relatively small amounts in general feed. When deficient, they often affect the utilization rate of other amino acids, so these amino acids are also called limiting amino acids.

Protein feed refers to feed in which the crude protein content in the dry matter reaches or exceeds 20% and the crude fiber content is lower than 18%. It is further divided into plant-based protein feed and animal-based protein feed. Plant-based protein feed is mainly composed of cakes and meals left after oil extraction from various oilseeds (mainly soybean, cottonseed, peanut, rapeseed and other cakes and meals); animal-based protein feed includes fish meal, meat meal and meat-and-bone meal, blood meal, leather meal, feather meal, silkworm pupa meal (powder), etc. The quality of protein is measured by the quantity and proportion of amino acids. The crude protein content and quality vary greatly among various feeds. In terms of content, it is highest in animal-based feed (40%-80%), followed by oil cakes (30%-40%), and relatively lower in bran and cereal grains (7%-13%). In terms of quality, the protein quality in animal-based feed, legume feed, and oil cake feed is relatively good.

When formulating compound feed, the application of protein feed should pay attention to the following issues:

1. Amino acid balance issue: the types, quantities, and mutual proportions of various essential amino acids in dietary protein match the needs of the animal, that is, amino acid balance. A protein with balanced amino acids is called an "ideal protein." When a diet is formulated according to "ideal protein," the utilization rate of dietary protein is relatively high, feed costs are relatively reduced, and @#@230@#@ benefits are relatively high.

2. Formulate diets according to digestible amino acids: most dietary amino acids cannot be completely digested. In many commonly used raw materials such as corn and soybean meal, about 90% of limiting amino acids can be digested, and differences may exist among individual amino acids. The amino acid digestibility of some plant protein feeds is very low, while the amino acid digestibility of animal protein raw materials varies greatly with different degrees of heating. At present, the data on digestible amino acids in feed are not yet very complete, and the determination of digestible amino acids is also affected by factors such as cecal activity of chickens, endogenous nitrogen loss, and urinary nitrogen loss, causing slight differences in measurement results. However, formulating diets according to digestible amino acids is the trend of future feed formulation. In this way, raw materials can be used rationally, poultry production performance can be improved, and environmental pollution from excreted nitrogen can also be reduced.

3. Synergistic effect among protein raw materials: in actual feed formulation, using more than 2 kinds of protein feed is better than using a single protein feed. For example, appropriately adding peanut meal and cottonseed meal to a corn-soybean meal diet makes it easier to balance amino acids, reduces the amount of limiting amino acids such as methionine, lysine, and threonine added, and lowers feed costs.

4. Some raw materials should be used in limited amounts: soybean cake contains trypsin inhibitor, urease, hemagglutinin, saponin, goitrogenic factor, anticoagulant factor, etc. However, most of these harmful substances are not heat-resistant and can be decomposed by heating under suitable moisture, thereby eliminating the harmful effects. Soybean meal contains fewer of these nutritional inhibitors, and its usage can reach 35%. Cottonseed meal contains nutritional inhibitors such as gossypol, cyclopropene fatty acids, phytic acid, and tannins. The amount of undetoxified cottonseed meal generally does not exceed 5%. Rapeseed meal contains nutritional inhibitors such as glucosinolates, sinapine, phytic acid, and tannins. General usage: chicks: 4%-5%; growing chickens: 7%-8%; laying hens: 5%-8%; later-stage broilers: 5%. It is prohibited to use spoiled and deteriorated animal protein feed, such as fish meal and blood meal contaminated with Salmonella.