Piglets' intestines are the main place to digest and absorb nutrients and play an important role in maintaining healthy growth of piglets. Because the digestive tract development of weaned piglets is still not perfect, it is sensitive to the changes of external factors. The huge stress caused by weaning and the change of feed morphology cause the intestinal mucosa to be destroyed, resulting in lowering of nutrient absorption rate and lowering of immune function. The growth and development of weaned piglets. Therefore, by analyzing the intestinal structure and function of piglets, it is of great significance to study the factors affecting the intestinal health of weaned piglets and the means of regulation.
1 pig intestinal structure and function
1.1 Morphological structure
Although the segments of the pig's digestive tract are different in thickness, thickness and shape, their basic structures are roughly the same. The digestive tract can be divided into four layers from the inside to the outside, namely the mucosa layer, the submucosa layer, the muscle layer and the serosa layer. The length of the small intestine of adult pigs is 15-20 m, which is 11-12 times of body length.
The mucosal layer is composed of epithelial, lamina propria and mucosal muscle layer structure. There are a lot of functional structures such as wrinkles, villi and microvilli on the surface of the mucosa. The intestinal mucosa is mainly composed of epithelial cells and goblet cells dispersed therebetween, and is the main part of the animal's absorption of nutrients. During the embryonic period, intestinal epithelial cells differentiate from cells in the intestinal submucosa, and differentiated cells remain in the crypt and undergo mitosis here. The mitotic cells gradually migrate from the crypt to the villi under the push 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 the feces. By continuous division and shedding, intestinal epithelial cells are always in a dynamic equilibrium. This process is called migration of intestinal mucosal cells, and the time required for migration is called cell turnover. The rate of metastasis of the ileum is higher than that of the jejunum because of its shorter villi. Mucosal epithelial cells are tightly connected, epithelial cells are constantly renewed, and their turnover rate is highest in all tissues. Adult animal intestinal epithelial cells were completely renewed 3-4d. Mature intestinal epithelial cells protrude at the top of the villi, and nascent animals require about 7-10 days of cell turnover, so that their epithelial cells are more difficult to recover than adult animals if they are damaged (Li Defa, 2003).
1.2 function
1.2.1 digestion and absorption
There are numerous fluff on the surface of the intestinal mucosa, and the outer layer of the villi is columnar epithelial cells. This epithelial cell has a special absorption capacity. Hundreds of microvilli are arranged at the edge of the intestinal lumen of the epithelial cells, which increases the absorption area by hundreds of times. The total surface area of ​​the intestine increases with the increase of mucosal folds, villi and microvilli. A 10-day-old, 3 kg-weight piglet has a 114 m2 absorption area in the small intestine. The microvilli are covered with glycoprotein to form a brush-like edge. They contain various digestive enzymes that hydrolyze carbohydrates and proteins. On the surface, there are many transport proteins, which absorb the digested and absorbed amino acids, glucose, salt and the like into the blood. If the villus top is damaged, the mature absorbed cells are lost, and the immature crypt cells produce a net secretion, which will result in a decrease in the functional area of ​​the mucosa and a decrease in digestion and absorption capacity.
1.2.2 Secretion of intestinal fluid
Small intestinal fluid is a mixture of various glandular secretions in the small intestinal mucosa. Pure intestinal fluid is a colorless turbid liquid, pH 8.2-8.7, containing sodium bicarbonate and various digestive enzymes, and 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 free digestive enzymes in the intestinal juice, and hydrolyze proteins, fats and carbohydrates into a form that can be utilized by the body.
1.2.3 barrier protection
Mucus composed of mucous epithelial cells and mucinous cells secreted by gelatinous glycoproteins has an important protective effect on the intestinal wall. Its function is: lubrication, to avoid mechanical damage to the intestinal mucosa; and to prevent acid and protease from affecting the intestinal mucosa. Erosion; provide a suitable living environment for normal flora; avoid damage from parasites and harmful microorganisms and toxins.
1.2.4 immune protection
Intestinal-associated lymphoid tissues include intestinal lymph nodes, lamina propria lymphocytes, and intraepithelial lymphocytes, which are the largest immune organs in animals and perform local immune function in the intestine. For example, the lamina propria lymphocytes are the site of the immune response, and S-IgA cells can be differentiated into IgA plasma cells under the synergistic induction of interleukins to produce S-IgA. S-IgA is the main immune defense factor against the invasion of pathogens on the surface of intestinal mucosa. It is also an important anti-inflammatory factor and plays an important role in maintaining the integrity of intestinal mucosa.
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2 factors affecting intestinal health
2.1 Dietary anti-nutritional factors
Dietary anti-nutritional factors include trypsin inhibitors, lectins, antigenic proteins, gossypol, phytic acid, etc. in soybean meal. The antigenic protein in soybean meal is the main cause of intestinal damage in piglets. Li et al. (1991) reported that globulin and β-conglycinin are the two most important antigenic proteins in soybean meal. The former stimulates mast cells to release histamine, causing increased permeability of epithelial cells and mucosal edema; the latter causes intestinal tract Morphological changes, manifested as intestinal villi atrophy, shedding.
2.2 pathogenic microorganisms
The gastrointestinal tract of newborn young animals is sterile, and then the microorganisms of the maternal and external environment are colonized in the intestine to form a relatively stable micro-ecological system. According to Mackie et al. (1999), there are about 400-600 microorganisms in 14 intestines in pigs, the number of which is 1014, which is 10 times that of somatic cells. Zoetendal et al. (2006) showed that the number of lactobacilli, lactic acid bacteria and Lactobacillus acidophilus was significantly reduced after weaning, because lactic acid bacteria requiring complex nutrient supply were affected by the decreased feed intake of piglets after weaning; On the other hand, changes in dietary composition, such as anti-nutritional factors and crude fiber contained in the diet, cause intestinal damage and inflammation, increasing the chance of infection by external pathogenic microorganisms.
2.3 Feed processing modulation
Weaned piglets undergo a huge transformation from feeding breastfeeding to feeding feed. Different feed processing methods have different effects on the intestinal health of piglets, such as raw material ripening, pellets and powders, and solid and liquid materials. Qi Zhigang et al. (2010) reported that from the perspective of digestibility, cereals and plant feeds (corn, soybean meal, soybean, wheat) need at least 50% ripening treatment to ensure starch gelatinization and antigenic Inactivated effect. After aging and granulation, the amount of anti-nutritional factors and pathogenic microorganisms in the diet can be reduced, thereby reducing allergic reactions and damage to the intestinal mucosa. Tang Renyong (2004) studied the effects of different shapes on the digestive physiology of weaned pigs. Compared with the powder, the pellets can significantly increase the daily feed intake of piglets and increase the activity of endogenous enzymes. Compared with solid materials, liquid materials It can significantly reduce the diarrhea of ​​piglets and increase the height of small intestine villi.
2.4 mycotoxins
Mycotoxins are toxic secondary metabolites produced by the toxin-producing molds in the growth and reproduction of food or feed, which have a great impact on the intestinal health of animals. Su Jun (2008) showed in vitro that deoxynivalenol (DON) and zearalenone (ZEN) in Fusarium toxin can cause oxidative damage in intestinal epithelial cells of newborn piglets and inhibit their proliferation, resulting in Damage to cell membrane integrity, inhibition of digestive enzyme activity and absorption of nutrients.
3 nutrition control measures
3.1 Freshness of raw materials
Feed crops may be contaminated by mold and mycotoxins in the fields, harvesting, storage, processing, etc., thus affecting animal health and production performance. When producing feed, the feed manufacturers should regularly check for mycotoxins, such as corn, corn gluten meal, fish meal, DDGS, etc., which are susceptible to mycotoxin contamination, and control the mycotoxin to a reasonable range. For corn and fishmeal that exceeds mycotoxins. It is necessary to make return processing in time. For the sake of the season, consider adding anti-fungal agents as appropriate to inhibit the growth of mycotoxins and ensure the freshness of raw materials.
3.2 Use of low antigen legume protein materials
In the nutrition research of weaned piglets, the selection of high-quality, low-cost, low-antigenic protein materials is one of the research hotspots. Soybean meal has high protein content, comprehensive nutrition and balance, but anti-nutritional factors such as antigen protein (globulin and β-conglycinin) cause allergies and damage to the intestinal tract of weaned piglets, resulting in diarrhea in piglets. Therefore, low-antigen bean protein raw materials, such as soy protein concentrate, fermented soybean meal, enzymatic hydrolyzed soybean meal, and expanded soybean meal, should be used to reduce the amount of common soybean meal in the diet of weaned piglets, thereby reducing the intestinal antigen to soybean antigen in piglets. Allergic reaction. Visser and Bremmers (1999) compared the effects of skim milk powder, fish meal, soy flour and soy protein concentrate on the apparent digestibility of protein ileum after weaning in piglets of different ages. The results showed that the ileal digestibility of the soy protein concentrate group was similar to that of skim milk powder and fish meal, which was significantly higher than that of the soybean meal group. Feng et al. (2007) showed that feeding piglets with fermented soybean meal not only improved the structure of intestinal villi, but also increased the activity of protease in the duodenum by 8.35%, the activity of amylase by 7.47%, and the activity of lipase. Increased by 4.68%, which promoted the digestion of the diet.
3.3 organic acids
Organic acids are usually divided into two categories: (1) Indirect reduction of the number of bacteria, such as fumaric acid, citric acid, malic acid, and lactic acid, can only be achieved by lowering the pH in the gastrointestinal tract. (2) not only can reduce the pH value of the gastrointestinal tract, but also inhibit Gram-negative bacteria, such organic acids can destroy the bacterial cell membrane and interfere with the synthesis of bacterial enzymes such as formic acid, acetic acid, propionic acid and sorbic acid. Organic acids play a huge role in reducing the pH of the gastrointestinal tract, increasing the activity of digestive enzymes, inhibiting the number of harmful bacteria, and improving the intestinal microflora. Tsiloyiannis et al. (2001) added 1.6% lactic acid to the diet of 28-day-old piglets. The mortality of edema disease in weaned piglets was reduced by 18.75%, and the ratio of beneficial bacteria to harmful bacteria in the small intestine was significantly increased. Hansen et al. (2007) added lactic acid and formic acid-based complex acids to the diet of weaned piglets. The test showed that the number of harmful bacteria in the gastrointestinal tract of piglets decreased by 29.13%. Li Peng et al (2009) added 0.3% lactic acid-type acidifier to the diet of weaned piglets. The test results showed that the small intestine villi height of the test group was increased by 20.91%, and the contents of E. coli and Salmonella were decreased by 4.62% and 4.08%, respectively. Serum IgG levels increased by 69.08%. This test shows that the acidifier protects the intestinal mucosa from damage by inhibiting the proliferation of harmful bacteria.
3.4 sodium butyrate
Short chain fatty acids (SCFA) include acetic acid, propionic acid, butyric acid, of which the main role is butyric acid. Butyric acid plays an important role in maintaining cell differentiation and intestinal epithelial cell integrity. Because of its freeness and volatility, it is made into a stable sodium salt-sodium butyrate in feed production. Kotunia et al. (2004) added sodium butyrate to the diet. The test results indicated that the villus height of the duodenum and ileum of the suckling pigs increased by 19.7% and 6.03%, respectively. Zhong Xiang et al (2009) added 2kg/t sodium butyrate to the diet of weaned piglets. The test results showed that the height of duodenum and jejunum villi in piglets increased by 23.9% and 6%, respectively. Niu Haihua et al (2009) added 1kg/t sodium butyrate to the diet of weaned piglets. The analysis of intestinal contents showed that the addition of sodium butyrate to the diet promoted the proliferation of intestinal lactobacilli and decreased the large intestine. The trend in the number of bacilli.
3.5 glutamine
Glutamine is a conditional essential amino acid, a major fuel for intestinal mucosal epithelial cells, and a nitrogen source for cell proliferation and differentiation. Under normal circumstances, glutamine is mainly taken from the intestines or circulation. Glutamine indirectly stimulates the secretion of hormones with intestinal nutrition, stimulates the release of peptide nutrients, and exerts its nutrient-promoting effect on intestinal mucosa. In addition, supplementation with glutamine can also reduce the permeability of intestinal epithelium under stress, stabilize the intestinal mucus, and maintain the need for intestinal mucosal metabolism and renewal under stress. Zhong et al (2011) orally administered 1 g of glutamine per kilogram of weaned piglets. The results showed that the duodenum and jejunum villus heights were significantly increased, and the diarrhea rate was reduced by 24% compared with the control group. Bianlian Congruent (2006) added 1.2% glutamine to the diet of weaned piglets. The results showed that not only the small intestine villus height and lamina propria thickness were significantly increased, but also the content of GSH (glutathione) in the small intestine increased. 12.37%, the content of CAT (catalase) increased by 5.83%, and the content of MDA (malondialdehyde) decreased by 18.02%, which protected the intestinal mucosa.
3.6 nucleotides
Nucleotides are the main components of the constituent cells and are the basic building blocks of DNA and RNA. They play an important role in the structure, metabolism and energy of cells. In vitro tests have shown that nucleotides can promote the proliferation of intestinal epithelial cells. In the early developmental stages of animals, small intestinal cells proliferate rapidly and are sensitive to nucleotides. Freshly weaned piglets are rapidly growing and stressed, and endogenously synthesized nucleotides do not meet the needs of intestinal mucosal DNA synthesis and mucosal growth and require additional addition. Zhang Yongqing et al. (2007) added 0.2% nucleotides to the diet of weaned piglets. The results showed that the height of duodenum and jejunum villi increased by 11% and 9.34%, respectively. The DNA content of duodenum and jejunum increased respectively. 1.26% and 111.93%.
4 summary
In summary, through the selection of high-quality raw materials, reasonable feed processing technology, and correct selection of nutrient metabolism agents, we can ensure the intestinal health of pigs and improve the production level of piglets. Of course, there are many factors affecting intestinal health, including genetic factors, energy factors, environmental factors, etc., and the means of regulation are not yet mature. By analyzing these factors, we explore and construct a theoretical system to achieve better technical systems and nutritional means to regulate the intestinal health of weaned piglets.
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