With the improvement of living standards, the national attention to the safety of meat quality is increasing day by day. The negative effects of high doses of antibiotics are highly regarded in the country. Limiting the use of antibiotics and seeking new alternatives have become the focus of animal nutrition scholars. Studies have shown that the addition of oligosaccharides to the diet has the effects of enhancing animal performance, improving immunity and reducing mortality (Chen Xi et al., 2011; Qi Guiling et al., 2008; You Jinming et al., 2010). As a new type of green feed additive, yeast mannooligosaccharide (MOS) is widely used in animal husbandry because of its strong stability, high safety and environmental protection, and overcoming the shortcomings of previous antibiotics and acidifiers. Etc., 2013).
1 yeast MOS
Currently, MOS for feed is mainly an extract of yeast cell walls. The MOS extracted from the yeast cell wall is an oligosaccharide composed of mannose or mannose and dextran through only α-1, 2, α-1, 3 and a-1,6 glycosidic linkages (Mitsuoka et al., 1987; Fishbein et al., 1998). The composition of MOS has a great influence on its physical and chemical properties. Under normal circumstances, it is easily soluble in water, insoluble in organic solvents, and precipitates when a certain amount of organic solvent is added.
Yeast cell wall-derived MOS is stable under physiological conditions, and MOS can withstand high temperature processing of feed processing (121 ° C, 20 min), and maintain its structural and functional integrity is not destroyed (Zhang Jiangang et al., 2012). MOS with low molecular weight has low viscosity in animals, is easy to transport and transport in the body, and digestive enzymes secreted by monogastric animals cannot decompose mannose. Flickinger et al (2000) found that MOS can directly enter the intestine and be selectively fermented by beneficial bacteria. MOS with relatively high molecular mass can not be used by probiotics, and has strong adsorption disease
The ability of the original bacteria.
2 MOS biological function
2.1 Interfering with pathogens to colonize H to reduce gastrointestinal diseases
Nathan et al. (1993) studied surface pounds, and the pathogenic bacteria (E. coli, Salmonella, and Clostridium, etc.) contained exogenous lectins on the cell wall or villi. These lectins can bind to sugar residues on intestinal wall cells. Specific binding occurs (D-mannose, β-galactose, L-fucose, etc.). Many intestinal pathogens such as Salmonella, Escherichia coli, Klebsiella, and Shigella flexneri have mannose-specific lectins (Ofek et al., 1978; Oyofo et al. 1989). Studies have shown that methyl-α-D-mannopyranoside has strong adsorption capacity with E. coli and has the ability to interfere with the colonization of E. coli (Ofek et al., 1978; Eshdat et al., 1981). Mirelman and other studies found that after E. coli adhered to the intestinal epithelial cell wall, the addition of oligomannose quickly sheds E. coli from intestinal epithelial cells, while common glucose and galactose have no effect. Since the probiotics of the intestine do not have a lectin specifically bound by mannose, MOS does not cause adhesion and elimination of beneficial bacteria. Intestinal probiotics have a competitive rejection relationship with intestinal pathogens. Because MOS effectively limits the colonization of intestinal pathogens, MOS has the function of promoting the growth and reproduction of intestinal probiotics and effectively maintaining the intestinal micro-ecological balance (Spring et al. , 2000).
2.2 Optimizing the intestinal micro-ecological environment
The digestion of carbohydrates by amylase in the gastrointestinal tract of monogastric animals is mainly limited to only -1,4 glycosidic bonds, and the ability to decompose other forms of glycosidic bonds is limited. The glycosidic bonds in yeast MOS are mainly α-1,2. Α-1,3 and α-1,6, therefore monogastric animals cannot decompose yeast MOS. Studies have shown that MOS can promote the growth of various Lactobacilli, and a large number of volatile fatty acids (acetic acid, propionic acid and butyric acid) produced by lactic acid bacteria can reduce intestinal pH and inhibit the proliferation of acid-sensitive pathogens (Flickinger et al., 2000; Spring et al. 2000). Yue Wenbin et al (2002) showed that MOS can significantly reduce the concentration of E. coli in the cecum and colon in piglets, and significantly increase the concentration of Lactobacillus and Bifidobacteria (P<0.05). Reduce the frequency of piglet diarrhea by 54%. MOS can promote the proliferation of intestinal probiotics by interfering with pathogens, effectively reducing intestinal pathogenic bacteria content, lowering intestinal pH, providing nutrients for intestinal epithelial cells, and promoting probiotics to better exert immunity, barrier and nutrition. And other functions.
2.3 stimulate the secretion of mannose-binding protein, activate the complement system
Ezekowitz et al (2003) believe that mannose-binding protein is an acute phase protein secreted by the liver, an important effect system and effect amplification system in the body, and an important part of the body's immunity. According to Janeway (1993), MOS has the ability to stimulate the liver to secrete mannose-binding proteins. Mannose-binding protein can specifically bind to a variety of glycoproteins with mannose residues and N-acetylglucosamine as terminal glycosyl groups on the surface of microorganisms, independent of antibody initiation regulation or complement activation level combination to protect themselves from Invasion of microorganisms and harmful substances (Gu Yuanyuan, 2008). Mannose-binding protein is the only lectin that can be found to activate the complement system. It is the natural immune factor of the body's first line of defense. It plays a huge role in activating the complement system, identifying pathogens and eliminating pathogens. If the body lacks enough mannose-binding protein, it will lead to repeated infections.
2.4 Improve cellular immunity and humoral immunity
Foreign studies have shown that piglets can increase the concentration of interleukin-2 in the blood after feeding MOS, and the activity of T lymphocytes and small intestinal lymphocytes are enhanced. At the same time, MOS can also promote the release of IFY from activated lymphocytes. -1 cytokine, which activates macrophages and causes them to move to the site of infection (Spring, 1998). There are also many domestic literatures showing that MOS can increase the conversion rate of PHA lymphocytes and the phagocytic power of phagocytic cells in animal organisms (Shao Liangping, 1999; Shao Liangping, 2000). Yue Wenbin et al (2006) on 35-day-old Duroc piglets showed that adding 0.3 010 MOS to the feed can increase the immune organ index of piglets and significantly improve serum immunoglobulin A (IgA) on the 7th day after weaning. Serum immunoglobulin M (IgM) levels on day 21 after weaning (P < 0.05). Xu Lei et al. (2012) showed that MOS significantly increased alkaline phosphatase activity, significantly increased serum globulin concentration, and significantly increased serum total antioxidant capacity compared with the control group (P< 0.05).
2.5 Adsorption of mycotoxins
In recent years, many literatures have shown that MOS has the effect of adsorbing mycotoxins, reducing the negative effects of mycotoxins on animal organisms, and not affecting the nutrients in the feed. Raju et al. (1998) showed that MOS had different degrees of adsorption on aflatoxin, zearalenone and ochratoxin in vitro, and the adsorption rates were 82.5%, 51.6% and 26. 4%. Zaghini et al. (2005) showed that MOS can adsorb aflatoxin Bl. Compared with the control group, MOS can reduce the absorption of aflatoxin Bl in the intestinal tract of laying hens and the level of aflatoxin Bl in tissues. .
3 Summary
The EU has completely banned the addition of antibiotics to animal feed, and domestic restrictions on the use of antibiotics have also increased. Finding new types of additives that can replace antibiotics has become the focus of the farming industry. Yeast MOS is a natural and stable new green feed additive. It has the functions of improving immunity, reducing pathogen colonization, promoting intestinal micro-ecological balance and adsorbing mycotoxins. MOS has the potential to reduce or replace the use of antibiotics.
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