Nutritional Regulation Methods for Improving Intestinal Health of Weaned Piglets

The intestinal tract of piglets is the main place for digestion and absorption of nutrients, which plays an important role in maintaining the healthy growth of piglets. Due to the development of the digestive tract of weaned piglets is not perfect, more sensitive to changes in external factors, weaning brought great stress and changes in feed form to the destruction of intestinal mucosa, resulting in reduced digestion and absorption of nutrients, decreased immune function, affecting the growth and development of weaned piglets. Therefore, it is of great significance to study the factors and control measures affecting the intestinal health of weaned piglets by analyzing the intestinal structure and function of piglets.

　　1Structure and Function of Intestinal Tract in Pigs

　　1.1morphological structure

Although the various sections of the pig digestive tract are different in thickness, thickness and shape, the basic structure is roughly the same. The digestive tract from the inside out can be divided4layer, namely the mucosal layer, submucosal layer, muscular layer and serosal layer. The length of the small intestine of an adult pig is15-20m, for body length11-12Times.

The mucosal layer is composed of epithelium, lamina propria and muscularis, and there are a large number of functional structures such as folds, villi and microvilli on the surface of the mucosal layer. Intestinal mucosa is mainly composed of epithelial cells and goblet cells scattered between them, which is the main site of animal absorption of nutrients. In the embryonic stage, the intestinal epithelial cells differentiate from the cells of the intestinal submucosa, and the differentiated cells stay in the crypt, where they undergo mitosis. The cells that complete mitosis gradually migrate from the crypt to the villi under the impetus of other cells, and finally reach the top of the intestinal villi and fall off, and the exfoliated intestinal epithelial cells enter the intestinal lumen and are excreted with feces. Through continuous division and shedding, intestinal epithelial cells are always in a dynamic balance. This process is called the migration of intestinal mucosal cells, and the time required for migration is called cell turnover. The transfer rate is higher in the ileum than in the jejunum because of its shorter villi. Mucosal epithelial cells are tightly connected, epithelial cells are constantly updated, and their turnover rate is the highest in all tissues. adult animal intestinal epithelial cells3-4dCompletely updated once. Mature intestinal epithelial cells protrude at the top of the villi, and cell turnover in newborn animals takes approximately7-10dTherefore, its epithelial cells are more difficult to recover than adult animals if damaged.

　　1.2Function

　　1.2.1digestion and absorption

There are numerous villi on the surface of the intestinal mucosa, and the outer layer of the villi is columnar epithelial cells, which have special absorption capacity. Hundreds of microvilli are arranged on the edge of the intestinal lumen of the epithelial cells, increasing the absorption area hundreds of times. The total intestinal surface area increases with the increase of mucosal folds, villi and microvilli. One10Age,3kgThe weight of the small intestine of the piglets has114m2Absorption area. Microvilli are covered by glycoproteins to form a brush border, which contains various digestive enzymes that hydrolyze carbohydrates and proteins. There are many transport proteins on the surface, which absorb amino acids, glucose, salt, etc. into the blood. If the top of the villi is damaged, the mature absorption cells are lost, and the immature crypt cells produce net secretion, the consequence will be a decrease in the functional area of the mucosa and a decrease in digestion and absorption capacity.

　　1.2.2Secretion of small intestinal fluid

Small intestinal fluid is a mixture of various glandular secretions in the small intestinal mucosa. Pure intestinal fluid is a colorless turbid fluid,pHValue8.2-8.7It contains sodium bicarbonate and a variety of digestive enzymes, and is mixed with exfoliated intestinal mucosal epithelial cells. These exfoliated epithelial cells are also rich in digestive enzymes, which participate in the digestive process in the small intestine together with the digestive enzymes free in the small intestine, hydrolyzing protein, fat and carbohydrate into a form that can be used by the body.

　　1.2.3Barrier protection

Mucus, composed of gelatinous glycoproteins secreted by mucosal epithelial cells and mucus cells, has an important protective effect on the intestinal wall, and its function is to lubricate and avoid mechanical damage to the intestinal mucosa.;Preventing the erosion of the intestinal mucosa by acids and proteases;Provide a suitable living environment for normal flora;Avoid being injured by parasites and harmful microorganisms and toxins.

　　1.2.4immune protection

Gut-associated lymphoid tissue, including the intestinal collection of lymphoid sections, the propria membrane lymphocytes and intraepithelial lymphocytes, is the largest immune organ in animals, in the intestinal tract to perform local immune functions. Such as the propria membrane lymphocytes is the effector site of the immune response, under the synergistic induction of interleukinS-IgAcells differentiateIgAPlasma Cells, ProducingS-IgAAnd play a role.S-IgAIt is the main immune defense factor to prevent the invasion of pathogens on the intestinal mucosal surface, and it is also an important anti-inflammatory factor, which also plays an important role in maintaining the integrity of the intestinal mucosa.

　　2Factors Affecting Intestinal Health

　　2.1dietary anti-nutritional factors

Dietary anti-nutritional factors include trypsin inhibitor, lectin, antigen protein in soybean meal, gossypol in cottonseed meal, phytic acid and so on, among which the antigen protein in soybean meal is the main cause of intestinal function damage in piglets.LiWait(1991)Reports, Globulin and Beta-Chaperin is the two most important antigenic proteins in soybean meal, the former stimulates the release of histamine from mast cells, causing increased epithelial cell permeability and mucosal edema;The latter causes intestinal morphological changes, manifested as atrophy and shedding of intestinal villi.

　　2.2pathogenic microorganism

The gastrointestinal tract of newborn animals is sterile, and then the microorganisms of maternal origin and external environment are colonized in the intestinal tract, which constitutes a relatively stable micro-ecological system.MackieWait(1999)The study found that about14a genus400-600species of microorganisms, the number reached1014A, is somatic10Times.ZoetendalWait(2006)The study showed that after weaning, the number of Lactobacillus, Forte's lactic acid bacteria and Lactobacillus acidophilus decreased significantly, which is due to the need for complex nutrient supply of lactic acid bacteria by the post-weaning piglet feed intake decreased.;On the other hand, changes in dietary components, such as anti-nutritional factors and crude fiber contained in the diet, cause intestinal damage and inflammation, and increase the chance of infection by external pathogenic microorganisms.

　　2.3feed processing modulation

Weaned piglets from breast milk intake to feed intake, experienced a huge change, feed processing methods are different, the impact on the intestinal health of piglets is also different, such as raw material maturation or not, granular and powder and solid and liquid feed. Ao Zhigang et al(2010)reported, from the point of view of digestibility, grain and plant feed(Corn, soybean meal, soybean, wheat)need at least50%The above aging treatment is to ensure the gelatinization of starch and the inactivation effect of antigen. After aging and granulation, the number of anti-nutritional factors and pathogenic microorganisms in the diet can be reduced, thereby reducing the allergic reaction and damage to the intestinal mucosa. Tang Renyong(2004)The effects of different material shapes on the digestive physiology of weaned piglets were studied, and compared with powder, granules can significantly increase the daily feed intake of piglets and increase the activity of endogenous enzymes.;Compared with solid feed, liquid feed can significantly reduce the diarrhea of piglets, improve the height of intestinal villi.

　　2.4mycotoxin

Mycotoxins are toxic secondary metabolites produced by toxigenic fungi in the growth and reproduction of food or feed, which have a great impact on animal intestinal health. Soviet Army(2008)Deoxynivalenol in Fusarium toxins, as indicated by in vitro tests(DON)and zearalenone(ZEN)It can cause oxidative damage to intestinal epithelial cells of newborn piglets, inhibit their proliferation, damage the integrity of cell membrane, inhibit the activity of digestive enzymes and the absorption of nutrients.