bile acids, which can significantly increase the trypsin and chymotrypsin activity of intestinal contents. In "Zhao Xiaofang, Zhang Hongfu. Physiological function of bile acids and their application in animal husbandry[J]", it was shown that after the added bile acids were absorbed into the liver through the enterohepatic circulation, they promoted the secretion of bile, thereby promoting the secretion of intestinal digestive enzymes, which could regulate the pH value in the intestine and enhance the activity of digestive enzymes. Jiulijia bile acid, protect the liver and gallbladder and intestines!
The intestinal tract is an important organ for the digestion and absorption of feed nutrients, and it is also an important immune protective barrier. Gut health is an important condition for efficient livestock and poultry production, maintaining high survival rates and producing high-quality products. In the post-antibiotic era of restricting and banning antibiotics, the intestinal problems of livestock and poultry are becoming increasingly prominent, especially under the conditions of poor environmental conditions of livestock and poultry breeding and lack of scientific feed nutrition in China, the incidence of intestinal diseases remains high, and comprehensive technical measures are needed to solve the intestinal health problems of livestock and poultry.
1. The relationship between intestinal health and immunity.
A healthy gut is the key to ensuring the health of livestock and poultry. A healthy gut requires the involvement of a large number of physiological and functional components, including nutrient digestion and absorption, host metabolism, energy production, gut microbial balance, mucus layer, barrier function, and mucosal immunity. A healthy gut is not just a disease-free gut, a healthy gut is also an efficient digestive organ that can effectively fight off disease and cope with change.
The intestine is the largest organ in livestock and poultry, and it is also the organ with the most extensive exposure to the surface of the organs in the body. It is a physical, chemical, immunological and microbiological selective barrier where digested feed and water are absorbed and disease-causing vectors are controlled. The intestinal tract is also the organ with the most immune cells in the body (nearly 70%), and most immune cells are located in gut-associated lymphoid tissue (GALT). These immune cells are the first line of defense against pathogens, and most of them are located in the large intestine. Immunity is defined as: "a physiological state that can defend against a specific disease, in particular by preventing the proliferation of pathogenic microorganisms or by neutralizing the effects of their products". Immunity is the body's internal line of defense against pathogen invasion. We can think of immunity as a fortress, the gut is the wall of the fortress, and the intestinal cells and mucosal barrier make up this wall, and the gut-associated lymphoid tissue (galt) is the tower equipped with the warrior, and the immune cell is the warrior, and the "authorized" food enters through several entrances to support the fortress (nutrient absorption). The enemies to defend against are various viruses, bacteria, and protozoa, and sometimes they also use poisons**, such as bacterial toxins or mycotoxins, to destroy the fortress. The symbiotic gut microbes are the natives inside the gut, preventing external enemies from invading the fortress while preventing them from attacking the city walls. The lungs are the sky above the fortress and their airborne defense mechanisms are active. Once the enemy has passed through the wall, there is an additional layer of defense inside the gut to prevent them from invading the wall. Obviously, this defense mechanism is intricate, takes a certain amount of time to establish, and is also easily damaged by numerous factors. 2. Composition of the intestinal barrier system.
The maintenance of normal intestinal barrier function depends on the intestinal mucosal epithelial barrier, intestinal immune system, normal intestinal flora, intestinal endocrine and peristalsis, among which the most critical barriers are the intestinal mucosal epithelial barrier and the intestinal mucosal immune barrier.
2.1. Mechanical barriers.
The barrier function of the intestine is maintained by well-organized intercellular structures, including tight junctions, adherent junctions, and desmosomes that surround the top of intestinal epithelial cells. The integrity of a healthy intestinal barrier is extremely important for protecting animals from microbial infections as well as for efficient nutrient absorption. 2.2. Chemical barriers.
The intestinal epithelial cells are mainly closely connected, and the alkaline phosphatase is densely distributed on the surface of the brush margin, which forms an intestinal barrier between the animal body and the outside world with the mucus and secretory Iga (SIGA) secreted by goblet epithelial cells, preventing the invasion of most foreign pathogenic pathogens. The acidic environment of the gut is also an important factor in inhibiting the reproduction of gut microorganisms. 2.3 Biological barriers.
There are more than 640 microorganisms in the gut of livestock and poultry, 90% of which have not yet been identified. It settles in different areas of the animal intestine, and the species and number are basically stable, on the one hand, it prevents the colonization and reproduction of foreign microorganisms or more virulent microorganisms; On the other hand, it stimulates the body to produce natural antibodies, which play a nutritional role in the host by helping digestion and synthesizing vitamins. 2.4. Immune barrier.
Secretory IgA is a major effector in the mucosal immune response. In addition to its ability to neutralize viruses and prevent bacteria and viruses from binding to mucous membranes, it also has the function of immune rejection, due to the presence of specific IgA, mucosal exposure to external soluble antigens can reduce the absorption of the same antigen, but has no effect on unrelated antigens. IE located in intraepithelial lymphocytes of the small intestine has intracellular granules similar to cytotoxic T cells and NK cells, and its main function is to kill cells, and at the same time, it has auxiliary activity to produce cytokines related to Th1 and Th2 functions. Intestinal epithelial cells can express major tissue-compatible antigens I, II and CD1 to perform antigen presentation functions. It is involved in the secretion of SIGA by producing secretory components (SC), which effectively transport SIGA from the lamina propria into the intestinal lumen. In addition, M cells can take up antigenic foreign bodies in the intestinal lumen and transport antigens through adsorption, pinocytosis and endocytosis, especially granular antigens to the tissues below them, and transport them to macrophages and dendritic cells in the fovele in the form of vesicles, which then provide antigens to lymphocytes to induce mucosal immunity. 3. Nutrients regulate the intestinal barrier.
Studies have shown that nutrition can regulate intestinal barrier function and maintain intestinal health. For example, our common butyric acid, glutamine, trace elements, prebiotics and oligosaccharides.
3.1 butyric acid.
Butyric acid plays an important role in regulating intestinal cell growth and differentiation, and the energy of intestinal mucosal epithelial cells comes from bacterial fermentation products, the most important of which is butyric acid, which is directly absorbed by colonic epithelial cells through a specific carrier-mediated transport system, produces butyryl-coenzyme through oxidation, and rapidly generates ketone bodies for ATP synthesis. At the same time, along with the absorption of water and sodium and the secretion of bicarbonate, it plays an important role in the preservation of water and electrolytes in livestock and poultry. Butyric acid does not need to go through a complex tricarboxylic acid cycle and directly provides maintenance energy to intestinal epithelial cells. Even in the presence of large amounts of glucose in the small intestine, butyric acid can still be used as the primary energy source for intestinal epithelial cells**. 3.2 trace element zinc (Zn).
ZN has been shown to play a very important role in maintaining the integrity and function of the gastrointestinal epithelial barrier in animals. The addition of ZN to the diet can reduce the intestinal permeability of humans and animals under conditions such as disease, malnutrition, stress and intestinal bacterial infection. However, Zn deficiency can lead to a decrease in the transepithelial resistance of Caco-2 cells and changes in tight junctions and adhesion junctions. Studies in poultry have shown that the addition of ZN (in the form of zinc sulfate) to the diet can significantly increase the villi height to crypt ratio and the expression of occludin and claudin-1 mRNA in the ileum of Salmonella typhimurium-infected broilers, and can effectively reduce plasma endotoxin levels, thereby slowing down the damage to intestinal barrier function caused by Salmonella infection. However, Hu et al. believed that zinc oxide and montmorillonite did not improve intestinal morphology, microbial number and barrier function. Compared with the control, montmorillonite, zinc oxide and zinc sulfate, the addition of 60 mg kg ZN in the form of zinc oxide montmorillonite complex significantly reduced the number of clostridium in the chicken intestine, significantly increased the rectal transepithelial electrical impedance, and significantly reduced the permeability of rectum to mannitol and ileum and rectum to inulin. 3.3 Probiotics and prebiotics.
Numerous human and animal trials have confirmed that probiotics and prebiotics can protect and improve intestinal barrier function. In recent years, research on the effects of probiotics and prebiotics on intestinal barrier function in poultry has also begun to increase. The addition of Saccharomyces boulardii and Bacillus subtilis B10 to broiler chicken diet significantly increased the mRNA expression of occludin, claudin-2 and claudin-3, and significantly increased the height and width of villi in the small intestine, the number of goblet cells, and jejunal IgA-positive cells, and significantly improved the intestinal interleukin-6 (IL-6), Tumor necrosis factor- (TNF-) interleukin-10 (IL-10), transforming growth factor- (TGF-) and SIGA content, thereby comprehensively improving intestinal barrier function. The mixed probiotic preparation composed of Lactobacillus salivarius and Lactobacillus reuteri significantly increased the depth of duodenal villous crypts and significantly decreased the depth of ileal villous crypts, thereby improving the morphology of intestinal villous tissues. The ability of intestinal mucosa to transport glucose and tissue conductivity were measured by Yuss perfusion chamber technology, and it was believed that the mixed probiotic preparation could increase the glucose transport between jejunum and large intestine, but had no effect on the conductivity of intestinal tissue, indicating that the mixed probiotic preparation improved its function while maintaining the intestinal epithelial barrier structure. Lactobacillus fermentum 1 2029 treatment reduced the degree of intestinal damage, improved the ileal epithelial microvilli, and increased the mRNA expression of claudin-1 and occludin, indicating that it has the effect of protecting intestinal barrier function.
3.4. Oligosaccharides.
In the healthy intestine of livestock and poultry, beneficial bacteria and harmful bacteria are in physiological dynamic balance, the balance changes in the stress state of animals such as abnormal climate and weaning, and harmful bacteria will become dominant bacteria to affect the health of animals, and the regulation of intestinal flora by oligosaccharides mainly lies in the proliferation of beneficial bacteria, especially bifidobacteria, inhibiting harmful bacteria, and promoting the phagocytosis and digestion of macrophages, so as to improve the health level of animals. 3.5 Glutamine.
Glutamine (GLN) is the main energy source of intestinal epithelial cells** and is necessary for the growth and differentiation of intestinal epithelial cells. It has been reported that GLN plays a role in maintaining, promoting, and protecting the intestinal barrier function in various models of enteritis in humans and rodents.
Summary
The intestinal barrier function is crucial to the health of livestock and poultry, and the research on the regulation of intestinal health through nutritional measures is worthy of our continuous in-depth study**.