Views: 33 Author: Site Editor Publish Time: 2023-04-25 Origin: Site
Feed antibiotics are considered the greatest biotechnology in animal husbandry production in the 20th century, with a history of over 60 years. Since the first report in the 1950s on the growth promoting effect of chloramphenicol on pigs, antibiotics have been widely used as antibacterial and growth promoting agents in feed abroad. Antibiotics have played a huge role in preventing and treating animal diseases, improving livestock and poultry productivity, and meeting the needs of human animal products. However, due to the development of antibiotic resistance by pathogenic bacteria, the residue of antibiotics in animal bodies and animal products, as well as the destruction of the ecological environment caused by the residue of antibiotics in the environment after animal metabolism, and the acceleration of the production of drug-resistant bacteria by this residue have attracted widespread attention. Therefore, since the 1960s, the use of antibiotics as feed additives has been controversial.
In 1974, the European Community banned penicillin, tetracycline, neomycin, streptomycin, chloramphenicol, sulfonamides, quinolones and other drugs from being used as feed additives. Sweden has completely banned the addition of antibiotics to feed since January 1, 1986. In April 1997, the European Union banned the use of averomycin; In January 1999, the use of tylomycin, virginiamycin, zinc bacitracin, and spiramycin as feed additives was prohibited. In January 2006, the last four antibiotics allowed to be used in feed (moneomycin, salinomycin, averomycin, and flavomycin) were also banned, and the European Union completely banned the addition of any type of antibiotic to feed. The Ministry of Agriculture of China released the first variety of feed drug additives in 1987, and the fourth edition of the "Guidelines for the Use of Feed Drug Additives" strictly distinguishes continuously added feed drug additives from short-term added varieties.
In recent years, the search for new feed additives that have similar antibacterial effects to antibiotics and are safe and harmless has become a hot topic in animal husbandry research. In recent years, some antibiotic substitutes have been continuously developed, and the research on yeast polysaccharides has also deepened with the development of science and technology. Domestic and foreign researchers have made many new achievements in the study of yeast polysaccharides, discovering that yeast polysaccharides have multiple important functional activities. This article mainly reviews the functional activity and application research of yeast polysaccharides.
Yeast polysaccharides are an important component of yeast cell walls, widely present in the cell walls of yeast and fungi, accounting for 40% of the dry weight of yeast cell walls. The main components of yeast polysaccharides are β- Dextran and mannan
Beta glucan is one of the main components of yeast cell wall, located in the inner layer of the cell wall. Most of it is a polymer composed of D-glucose bound through beta-D - (1-3) bonds, while a small portion is a highly branched beta-D - (1-6) bond bound glycan that is insoluble, unabsorbable, and does not produce viscosity in the digestive tract. In the cell wall of yeast β- Glucan can participate in immune regulation and enhance the body's non-specific immunity. Through phagocytosis, it can absorb, destroy and eliminate damaged, aging and dead self cells and pathogenic microorganisms invading the body, increase the ability of animal body to produce natural killer cell and improve the survival rate.
Mannan is located in the outer layer of the cell wall and consists of 2-10 monosaccharides, with the monosaccharides separated by α- 1,2、 α- 1,3、 α- The 1,6 keys are connected, and the main chain is α- 1,6 engagement, side chain is α- 1,2 and α- 1,3 engagement. The mannan in the yeast cell wall can specifically cut off the main chain through selective acetylation reaction α- (1,6) - glycosidic bond, which generates several kinds of oligosaccharides, namely mannan oligosaccharides (MOS for short). MOS has functions such as optimizing the microecological environment of animal gastrointestinal tract, reducing gastrointestinal diseases, and activating immunity.
Yeast polysaccharide is a broad-spectrum immune enhancer, which can significantly improve the anti disease and anti stress ability of the body, and significantly increase the number of lactobacilli in the intestinal tract, while reducing the number of Escherichia coli; Promote vitamin synthesis and stimulate intestinal peristalsis, assist in food digestion and nutrient absorption. Yeast polysaccharides can also promote animal metabolism, avoid excessive intestinal decay, reduce serum endotoxin levels, and promote the growth and development of the body. Yeast polysaccharides have the characteristics of being insoluble and non absorbable during the digestion process. They can be used instead of antibiotics to promote the growth and development of piglets and improve disease resistance. Tan Benjie et al. (2011) added 0.15% yeast polysaccharides to the diet of broilers, which showed the most significant weight gain effect, increasing by 6.66% compared to the control group. Li Haiyan et al. (2004) added 0.8% yeast polysaccharides to the feed of high-yield crucian carp, and the results showed that the body length and weight of high-yield crucian carp were significantly increased, and they could effectively resist the occurrence of red skin disease, greatly improving the survival rate of fish.
Yeast polysaccharides have non-specific immune effects, and their use can stimulate the development of host immune organs and accelerate immune maturation. It can fully develop the lymphoid tissue, strengthen the lymphocyte reproduction ability, promote the formation of plasma cell, increase the time of immunological memory, and activate megalophils. Therefore, yeast polysaccharides are a broad-spectrum immune enhancer that can enhance the cellular immune capacity of animals and enhance their humoral immune response levels. It can significantly improve the body's ability to resist disease and stress. Gao Shiying et al. Zhu Yanjun et al. (2009) studied the effect of yeast polysaccharides on the proliferation activity of mouse spleen cells in vitro. The results showed that yeast polysaccharides had a significant proliferation effect on T and B lymphocytes, and could significantly improve the function of the mouse immune system.
Yeast polysaccharides have a certain regulatory effect on the gut microbiota of animals. It is mainly manifested in the following aspects: yeast polysaccharide has the ability to adsorb pathogenic bacteria, which can reduce the number of pathogenic microorganisms in animals' intestines, such as Salmonella and Escherichia coli, promote the reproduction of lactobacillus in the intestinal flora, and make the dysfunctional flora in the intestinal tract corrected and restored in a short time; Eliminate pathogenic microorganisms such as Escherichia coli and Salmonella that invade the body through the immune function of the body; By regulating the balance of the body's microecology, it promotes the proliferation of beneficial physiological active bacteria that are Gram positive in the intestine, inhibits Gram negative saprophytic bacteria, and effectively reduces the content of endotoxin in plasma, achieving the goal of reducing serum endotoxin levels, inhibiting the colonization of exogenous bacteria in the intestine, and preventing the transfer of Gram negative bacteria from the intestine to the outside (Dong Xiaoying et al., 2005). Wang Yunchao (2005) confirmed that adding appropriate dosage of brewer's yeast and yeast polysaccharide to the feed can improve the antibody level of ND vaccine and Escherichia coli vaccine for laying hens and improve the intestinal environment.
Generally speaking, young animals have immature immune organs, relatively low immune function, and poor resistance to various stresses, especially young birds. Therefore, it is of great significance for young birds to promote the rapid development of their immune organs by feeding immune enhancing factors. The research results of Wang Yuanxiu et al. (2011) showed that the optimal extraction conditions of yeast polysaccharide were pH 7.2, temperature 40 ℃, citric acid concentration 0.02mol/L, and the main component of the extracted polysaccharide was glucan. The thymus index, spleen index, bursa of Fabricius index, and cecal tonsil mass or volume of the test group chickens were significantly increased compared with the control group, indicating that yeast polysaccharide had a significant role in promoting the maturation of the chicken immune system.
At present, there may be several factors that affect the effectiveness of yeast polysaccharide use: firstly, the effective substance content of yeast polysaccharide. Different types of yeast, manufacturers, and extraction methods may all affect the content of active ingredients in yeast polysaccharides. The second is the addition time and amount of yeast polysaccharides. In general, continuous use with a certain amount of stimulation is sufficient. However, in cases of epidemic or stress, it can be doubled in a short period of time and fed directly or after granulation. The third is that the amount of animals added varies among different species, age stages, physiological stages, and environments. There should be differences in practical applications.
In summary, yeast polysaccharides can balance the gut microbiota and enhance immunity, making them an immune enhancer with dual effects of antibiotics and probiotics; In production, it can significantly enhance the disease resistance of animal bodies; Improve the production performance of animals, improve economic benefits, and have no pollution, drug resistance, and non-toxic side effects. With the continuous deepening of research on yeast polysaccharides, their practical applications are becoming increasingly popular and will play a huge role in increasingly strict animal production in the future.
