The research and application of feed additives is a major issue related to the sustainable development of animal husbandry and the quality of human life. In order to meet the demands of international and domestic markets for green food, it is important to make full use of China's abundant plant and microbial resources to develop a “green†feed additive industry and promote the construction of a safe animal production system. Looking at the development of the world feed industry, every new feed additive technology has brought the feed science and technology level to a new level. In order to ensure the effective operation of safe animal production systems, the application of "green" feed additives has become the key to the production system. At present, the widely used "green" feed additives are mainly oligosaccharides, Chinese herbs, feed enzymes, biological viable bacteria, organic acids and organic trace elements.
Glycan additives
Oligosaccharides are non-degradable carbohydrates that are water-soluble and have a small number of molecules. Different forms of oligosaccharides form oligosaccharides, mannan-oligosaccharides, xylo-oligosaccharides, galacto-oligosaccharides, and isomaltose. Oligosaccharides. Because this kind of material has the similar function to the live bacterium preparation, some people call it "chemical probiotics". In recent years, modern biotechnology has been used to combine the production of synbiotics with oligosaccharides and biogenic microbial preparations. In the mid- to late-1980s, Japan first developed oligosaccharides as feed additives and used them in the feed industry. In the mid-1990s, one-third of the oligosaccharides produced in Japan were used as feed additives, and 40% of pig feed was supplemented with these substances. In the late 1990s, the feed industry in China began to research and develop oligosaccharides, which has become a new growth point for feed additives. Oligosaccharides have no residues, no toxic and side effects, and have the potential to become alternatives to antibiotics. They are very promising additives. At present, there are many researches on the use of feeds such as fructooligosaccharides, oligosaccharides, and xylo-oligosaccharides. According to comprehensive reports, after the use of oligosaccharides, animal growth has increased to varying degrees, and the feed-to-meat ratio has decreased. The rate of death scouring is reduced.
Physiological action mechanism of oligosaccharides feed additive: (1) Selectively proliferate bifidobacteria and other animal intestinal beneficial bacteria. The use of oligosaccharides in the intestinal tract of animals produces a large number of proliferating oligosaccharides, resulting in a competitive advantage for microorganisms. At the same time, short-chain fatty acids such as acetic acid and lactic acid and some antibacterial substances are produced, which directly inhibit Salmonella, Shigella, and gas production in the intestinal tract of animals. Clostridium perfringens, Escherichia coli and other spoilage bacteria and exogenous pathogenic bacteria growth and proliferation, reduce the damage of harmful organisms to animals, and ensure the health of animals. 2 Oligosaccharides can adsorb intestinal pathogens and promote their excretion through the feces. Studies have shown that many pathogenic bacteria have an exogenous coagulation protein (a type of protein for recognition) on the surface that binds free carbohydrates (receptors) that are present on the cell surface. The process of pathogenic bacteria harming animals must first be combined with the carbohydrates on the surface of intestinal wall cells through this exogenous coagulation protein before they can adhere to the intestinal epithelium. The pathogens that adhere to the intestinal epithelium can rapidly proliferate. The carbohydrates on the surface of the intestinal wall cells of animals are short-chain branched carbohydrates. When oligosaccharides enter the animal's intestine, they bind competitively to the exogenous coagulin on the surface of pathogens, thus preventing the pathogens from being found in animals. Adhesion on intestinal epithelial cells promotes the excretion of pathogenic bacteria with the feces, reduces the concentration of bacteria in the intestinal tract of animals, and reduces the damage of pathogens to animals. 3 The proliferation of beneficial bacteria using oligosaccharides can promote the activity of phagocytic cells in animals and enhance the immune function of animals. 4 Oligosaccharides can also bind to bacteria, viruses, etc., and act as adjuvants to these foreign antigens, slow down the absorption of antigens, increase the titer of the antigen, and enhance the host's immune function. 5 The use of the beneficial bacteria of oligosaccharides can synthesize B vitamins and at the same time promote the use of other nutrients by animals.
Mannan oligosaccharides are oligosaccharides composed of several mannose molecules or mannose and glucose through α-1,2, α-1,3, α-1,6 glycosidic bonds. It is generally obtained by yeast cell wall fermentation enriched with mannooligosaccharides. Mannan oligosaccharides can improve the performance and health of poultry, pigs and cattle by promoting the health of the gastrointestinal tract. Studies have shown that mannose-oligosaccharides can inhibit Escherichia coli, Salmonella typhimurium, Clostridium botulinum, Clostridium spp. and other pathogens; Promote the growth and reproduction of Bifidobacterium longum, Lactobacillus casei, Lactobacillus acidophilus and Lactobacillus delbrueckii. In E. coli, 66% of the cells contained mannose-sensitive pilus, and Salmonella typhi and Salmonella enteritidis adhered to the mannose receptor accounted for 80% and 67% of the test bacteria, respectively.
In vivo animal experiments showed that mannose-oligosaccharide reduced the concentration of Salmonella typhi in the cecum by 2 logarithmic units, and that E. coli pathogenic bacteria in cecum type I pilus decreased from 75% to 15%, reducing the infection of Salmonella with livestock in Dublin. . Mannan oligosaccharides have a strong ability to adhere to harmful bacteria. Mannan oligosaccharides can promote the activity of animal macrophages, enhance non-specific immune systems, and increase the ability to phagocytose and kill invading microorganisms. After ingesting mannooligosaccharides in sterile pigs, the concentration of immunoglobulin in intestinal tissue increased by a factor of four. After mannose-oligosaccharides were fed, the digestibility of cellulose in broiler chickens was increased, the depth of the follicles in the turkey intestinal tract was decreased, the length of the villus was increased, the epithelial cell turnover rate was decreased, and the energy conservation was used to increase the body weight and improve the feed conversion rate. .
Xylo-oligosaccharides are straight-chain sugars in which 2 to 6 xylose are bound by β-1,4 bonds. It is generally extracted from natural plants. After hydrolyzing the cellulose contained in the natural plant (enzymatic or physical method, etc.), the low molecular weight xylooligosaccharides with different molecular weights, such as xylobiose, xylotriose, xylotetraose, and xylopentose, are separated according to need. The effective component of xylose products. Xylo-oligosaccharides have a wide range of sources of raw materials. In particular, by-products of crops such as stems, leaves, husks, rice bran, etc. can be used. Compared to other functional oligosaccharides, xylo-oligosaccharides have the following characteristics: 1 Xylo-oligosaccharides are difficult to break down by animal digestive enzymes. 2 Highly selective proliferation of Bifidobacterium. 3 has a unique acid stability and thermal stability. Studies have shown that: 5% of xylo-oligosaccharide solution in the range of pH 2.5 ~ 8.0, no significant change after heating for 1 hour; pH value of about 3.4 xylose-containing acidic feed stored at room temperature for 1 year, which is low The amount of xylose retained was more than 97%. 4 The compatibility with feed is good, and if it is added in small quantities, it can exert good effect. The experiment found that the addition of xylo-oligosaccharides to layer chicken diets can significantly increase the average daily egg production rate and laying weight of laying hens; significantly reducing the ratio of material to eggs of laying hens, and the feed remuneration increases by 3.6% to 5.7%. There is no significant effect on egg quality.
Fructooligosaccharides are oligosaccharides formed by the binding of sucrose molecules by β-1,2 glycosidic bonds to 8 or less D-fructose, and are mainly used for feed additives, including fructose, fructose, and oligopentaose. They are found in nature at higher concentrations in plants and yeasts such as barley, wheat, rye, potatoes, lettuce, bananas, onions, chicory, and the like. Studies have shown that FOS has the functions of improving the absorption of nutrients and feed utilization of livestock and poultry, and promoting the growth and production of livestock and poultry. Experiments have found that adding 0.17% fructo-oligosaccharides to the diet can increase the daily gain of the pigs by 3.88% and the feed-to-weight ratio by 4.67%; 0.2% fructo-oligosaccharides can significantly increase the daily gain and feed intake of the weaned pigs. Reduce the feed-to-weight ratio and the incidence of diarrhea in weaned pigs to increase economic efficiency.
Herbal additives
In the early 1980s, herbal additives began to be used in feeds. In recent years, with the introduction of regulations restricting or prohibiting the use of antibiotics in the European Union and some countries, Chinese herbal medicine and plant extract additives have become the first-choice alternatives for antibacterial substances in feeds. Chinese herbal medicine has become one of the most important feed additives for people.
Chinese herbal medicine has both nutritional and medicinal properties. It has the functions of regulating the metabolism of animal body, invigorating the spleen and stomach, inhibiting bacteria and sterilizing, strengthening the body's immunity, supplementing and regulating nutrition, promoting the growth of animals and improving feed utilization. Compared with other feed additives, Chinese herbal additives have unique advantages: 1 Wide range of resources, raw materials are cheap. 2 The efficacy is stable, and a variety of herbs are combined to exert the comprehensive effect of treatment. 3 Herbs are not only nutritious but also non-nutritional and fully functional. Tests have shown that Chinese herbal medicine additives can replace antibiotics, and do not require withdrawal period and safe use; Chinese herbal medicine also has anti-oxidation, anti-mildew and other functions, can promote animal growth and increase feed remuneration. 4 no toxic side effects, no drug resistance. Most of the active ingredients in Chinese herbal medicine are in organic state, such as oligosaccharides, polysaccharides, alkaloids, polyphenols, and flavonoids. They are digested, absorbed, and redistributed by animal organisms. They are not resistant to pathogens and parasites, and there is no drug residue in the body. , It can be used continuously for a long time and it is a "green" feed additive with no residual pollution.
China has developed many varieties of Chinese herbal medicine and plant extract additives. There are roughly 200 kinds of herbs used in additives, including anti-inflammatory, anti-bacterial, immune enhancement, and digestion. However, in production, due to different sources of herbs, processing methods, etc., the active ingredients change greatly, and the quality control standards are lacking. In addition to the problems of drug source, volume, dose, side effects of long-term use, synergy with other additives, etc., the extraction and concentration of effective ingredients in the production of Chinese herbal medicine additives, the enhancement of application effects, and the reduction in the amount of feed added have become Research hotspots.
Feed enzyme preparation
Enzymes are a class of biocatalytic proteins. Feed enzyme preparations mainly include two major categories: one is exogenous digestive enzymes, including proteases, amylases and lipases. Its function is mainly to supplement animal endogenous digestive enzymes and improve the digestibility of feed nutrients. The other is exogenous degrading enzymes, which cannot be synthesized in animal tissue cells, but microorganisms can synthesize them. They include cellulase, hemicellulase, β-glucanase, xylanase and plant. Acid enzymes and so on. Its main function is to degrade anti-nutritional substances or substances that are difficult for animals to digest or completely indigestible, improve feed utilization, and reduce pollution of the aquaculture industry to the environment. Due to the specificity of enzyme selection for substrates, its application effects are closely related to feed components, animal digestive physiology, etc. Therefore, the selection of enzyme preparations should be based on the specific feed and livestock species and their age physiological stages, and Avoid high temperature and other environmental influences during use.
At present, commercial feed enzymes are generally stabilised preparations and are mostly used for pigs, poultry and yaks. At present, there are nearly 30 companies in China that produce single or complex feed enzyme preparations, and the production of feed enzyme preparations has come a long way. Feed enzyme preparations are non-toxic, non-residue, and degradable. The use of enzyme preparations can not only improve the production performance of livestock and poultry, fully tap the utilization of existing feed resources, but also reduce the emissions of organic matter, nitrogen and phosphorus in livestock manure, and ease the development of animal husbandry and the protection of the ecological environment. Contradictions, broad prospects for development and application. With the development of feed science and biotechnology, more enzyme preparations will be used as feed additives in the future. The potency of enzymes and heat resistance of enzymes will also be constantly improved and improved, making them more suitable for the development of the feed industry. need.
(Author: Wang Tian College of Animal Science and Technology, Nanjing Agricultural University)