An overview of proteins in the nutritional needs of pigs

(I) carbohydrates

Carbohydrate is the most widely sourced and accounts for the largest proportion of nutrients in the diet, and is the main source of energy for pigs. In cereal feed, there is little soluble grass sugar and disaccharide, mainly starch, so it is the main energy source of pigs. Starch is converted into glucose by amylase in the digestive tract and then absorbed into the blood to form blood sugar. Biooxidation and energy supply in the body. The digestibility of soluble sugar and starch in livestock is 95% to 100%. The growth of piglets fed with large amount of starch feed was poor due to the lack of pancreatic amylase and intestinal disaccharidase secreted by the pancreas in the digestive tract of piglets before 3 weeks of age. Before 7 days old, feeding glucose and lactose piglets can be used effectively. Fructose and sucrose can be used after 10 days of age, but feeding young pigs generally lead to severe dysentery, weightlessness and high mortality. Crude fiber, after a certain concentration of acid and alkali treatment, the remaining residue is called crude fiber, the determination of this method is incorrect, the general feed crude fiber contains cellulose, hemicellulose and lignin, and its composition proportion is unstable. The contents of cellulose, hemicellulose and lignin in typical feed crude fiber are 50%, 80%, 20% and 10% 50%, respectively. Cellulose and hemicellulose are polysaccharides. Cellulose is a glucose polymer and hemicellulose is composed of hybrid sugars (glucose, fructose, mannose, galactose, digebose, xylose, rhamnose, uronic acid). Lignin is a group of complex and indigestible polymers of ─-phenyl (phenyl) propane derivatives. These substances are the main components of plant cell wall. Neutral detergent fiber (NDF) in VanS0esf analysis estimated that the total plant cell wall was mainly composed of cellulose, hemicellulose and lignin, acid detergent fiber (ADF) included cellulose and lignin, and the difference between NOF and ADF was hemicellulose in feed. There is no enzyme to digest fibrin in the small intestine of pigs, and it cannot digest cellulose, hemicellulose and hemicellulose, but the main tail product digested by the fermentation of crude fiber to the large intestine is volatile fatty acids, which provides about 5% and 28% of the energy needed to maintain energy. The digestibility of crude fiber is generally 30%-39%, and its digestibility depends on the source of fiber. The Lignification degree, dietary content and processing degree were affected by the degree of Lignification, dietary content and processing degree, so there was a great variation. The utilization of fiber was affected by dietary physical and chemical composition, dietary nutrition level, animal age and so on. The variation of crude fiber digestibility was 0-97%. There is no empty theory on the dietary fiber level of growing and finishing pigs. It is generally believed that the dietary crude fiber level of growing pigs with about 20kg weight is 6%, and that the neutral detergent fiber level of low lignin should be less than or equal to 15%. Some experts believe that the level of crude fiber in sow diet is 10%-12%. The high level of crude fiber in diet decreased the digestibility of organic matter and energy in feed. An increase of 1% crude fiber in the diet reduces the total energy digestibility by 3.5%. It has also been reported that it has an effect on protein digestibility. In the later fattening period, a higher level of crude fiber could be used to limit the feed intake, which could reduce the deposition of body fat and improve the body quality. the content of crude fiber in the diet increased by 1%, and the thickness of backfat decreased 0.5mm.

(2) Esters

Esters include fat and oil, feed generally contains about 5% fat, fat is high in energy, 2.25 times the calorific value of carbohydrates, pigs deposit a lot of fat, mainly body tissue synthetic fatty acids. The main raw material for the synthesis of fatty acids is acetyl-CoA, which mainly comes from glucose, the decomposition product of sugars in feed. Fat and some amino acids can also produce acetyl-CoA. Triglycerides were synthesized from acetyl coenzyme A. However, pigs can not synthesize some fatty acids, which must be supplied by diet or formed by specific precursors in the body, and are called essential fatty acids (EFA), which play an important role in protecting the normal function and health of the body. Essential fatty acids include linoleic acid (octadecadienoic acid), linoleic acid (octadecatrienoic acid) and arachidonic acid (eicosatetraenoic acid). Linoleic acid must be supplied from the diet, and the last twenty essential fatty acids can be supplied directly from the diet. Linoleic acid can also be synthesized by intramolecular conversion of sufficient linoleic acid from the body. The mechanism of essential fatty acids in vivo is not clear, wing essential fat deficiency is characterized by skin damage, the appearance of horny scales, capillary blood becomes fragile, immunity decreases, growth is blocked, and young and fast-growing animals are more sensitive. Pigs can get the necessary essential fatty acids from feed, which is rich in essential fatty acids in common feed and generally will not be lacking. NRC stipulates that the linoleic acid requirement of pigs accounts for 0.1% of the diet. 30kg and 30~90kg weight pigs are required for essential fatty acids of 3% and 1.5% of dietary digestive energy, respectively. It is reported that for 5-week-old weaned pigs to 90 or 100kg weight pigs, the linoleic acid requirement for maximum growth and optimal feed utilization is 0.2% of total energy or 0.1% of diet.

Protein and amino acid protein are important components of cells, which involve most of the life-related chemical reactions of animal metabolism and play an important role in the process of life. Protein is not only the structural component of the body, the main raw material for tissue renewal and repair, but also the components of enzymes, hormones, immunity and resistance. Protein can be transformed into energy supply or into sugar and fat in the body. Protein is a large number of nutrients composed of amino acids. Animal need for protein, substantial need for amino acids. The physiological functions of proteins are completely consistent in organs, body fluids and other tissues, and the main differences are caused by different amino acids, quantities and binding modes of proteins. Animal proteins are different from plant proteins, but the proteins needed by animals come from plant proteins. About 30% to 70% of the protein needed by animals is supplied by protein in cereal feed, and the rest must be met by plant meal feed. The protein in feed generally refers to crude protein, that is, the amount of nitrogen in feed multiplied by 6.25 is crude protein. Its definition is mainly based on the assumption that 100g protein contains 16g nitrogen.

(3) essential and non-essential amino acids

There are about 20 kinds of amino acids that make up animal proteins, some of which are synthesized in animals, while others cannot be synthesized; they must be supplied from feed, so amino acids are divided into essential amino acids and non-essential amino acids. The amount of amino acids that cannot be synthesized or synthesized in the body can not meet the physiological needs of pigs, and the amino acids that must be provided by feed are called essential amino acids. Studies have shown that growing pigs need 10 essential amino acids (lysine, methionine, tryptophan, histidine, isoleucine, leucine, phenylalanine, tryptophan, threonine and arginine). Adult pigs can synthesize enough arginine, 50% of methionine requirements can be replaced by glutamic acid, and 30% of phenylalanine requirements can be replaced by glutamic acid. Therefore, cystine and phenylalanine are called semi-essential amino acids. However, it should be noted that cystine and phenylalanine cannot be converted into methionine and glutamic acid. Non-essential amino acids are not pig nutrition. Up and down, but in pigs, the amino acids needed in the body can be synthesized from other amino acids or nitrogen sources. Thus it can be seen that the ability to provide sufficient essential amino acids and non-protein nitrogen to synthesize non-essential amino acids in feed determines the appropriate level of feed protein. The actual protein requirement of pigs is the need of essential amino acids and synthetic non-essential amino acid nitrogen sources.

The nutritional value of feed protein mainly depends on the composition and content of essential amino acids in feed. The more the content and proportion of essential amino acids in feed are close to the content of essential amino acids in pigs, the nutritional value of feed protein is higher, and the quality of feed protein from different feed sources is different. The deficiency of one or some amino acids in feed protein will limit the use of other amino acids, which is called restricted amino acid. In a certain feed or rations, the smallest ratio of an amino acid to the amino acid needed by pigs is the first limited amino acid, a little larger is the second limited amino acid, and so on. The common limited amino acids in pig feed are lysine, methionine, tryptophan, threonine and isoleucine. The first limiting amino acid in pig diet is lysine. In the diet, the combined use of several kinds of protein feed can play the complementary role of protein, improve the utilization rate of feed protein or the biological value of protein, and the addition of synthetic amino acids can improve the biological value of feed protein. Lysine is the commonly deficient amino acid in the day of plant protein source, so lysine is often added to pig diet.