With the development of modern intensification and large-scale aquaculture, the risk of aquatic animals infecting various diseases has increased greatly. In order to prevent aquatic animal diseases, promote the growth and development of aquatic animals and improve feed utilization, a large number of antibiotics and other drugs are used as feed additives. However, with the long-term, large-scale use of antibiotic additives, the negative effects are increasingly exposed. Therefore, the research and development of green feed additives that can replace antibiotics with strong functions, low prices, excellent performance, non-toxic side effects, and environmental protection have attracted wide attention of researchers.
First, the side effects of antibiotic feed additives
1. Long-term use of antibiotics causes bacteria to develop resistance
Although the frequency of drug resistance factor transmission is only 1/106, due to the large number of bacteria and rapid reproduction, at this frequency, the spread and spread of drug-resistant strains are still caused, and a variety of drug resistance can be produced in one cell. . Antibiotic abuse leads to an increase in resistant strains, and long-term, large-scale unreasonable use of antibiotic feed additives is the main reason. In aquaculture, some bacterial diseases that were not severe or less frequent in the past have now risen to the main infectious diseases of aquatic animals, which is directly related to the long-term abuse of antibiotics.
2. Long-term use of antibiotics leads to decreased immunity of aquatic animals
A large number of antibiotics will be distributed to various tissues and organs with the blood circulation after being ingested into the body, and the immunity of the aquatic animal body will be gradually weakened. Antibiotics also cause a decrease in the quality of the antigenic body, which directly affects the immune process, thereby adversely affecting the vaccination of the vaccine.
3. Long-term use of antibiotics causes residues in aquatic products and the environment.
After the antibiotics are absorbed into the body, the metabolic pathways are various, mainly based on liver metabolism, and excreted from the feces by bile. Some stable antibiotics are released into the environment, causing environmental drug residues. The remaining drugs are accumulated in the human body and other plants through aquatic products and the environment, and finally collected in the human body in various ways, resulting in a large number of drug-resistant strains in the human body, losing resistance to certain diseases, or generating a large amount of accumulation on the body. Toxic effect.
Second, green aquatic feed additives and their applications
1, live bacteria preparation
The live bacterial preparation is a microbial agent produced by industrial anaerobic fermentation of beneficial bacteria of animals. The mechanism of action of live bacterial preparations on aquatic animals can be summarized as follows: After the beneficial microorganisms in the live bacterial preparation enter the aquatic animal body, they form a dominant flora, compete with harmful bacteria for oxygen, attachment sites and nutrients, and competitively inhibit harmful bacteria. Growth, thereby regulating the intestinal flora to normalize; microbial metabolism produces organic acids, lowering the pH value in the intestine, killing acid-resistant harmful bacteria; producing lysozyme, hydrogen peroxide and other substances, can kill potential pathogens; Various digestive enzymes are beneficial to nutrient decomposition; synthesis of B vitamins, amino acids, unknown growth factors and other nutrients; directly stimulate intestinal immune cells to increase local immune antibodies and enhance the body's disease resistance. The use of live bacterial preparations in aquaculture is characterized by the following three directions: The first is the diversity of functions, which promotes growth and increases the yield of aquatic products such as fish, shrimp and crab. According to reports, it can increase production by 10-30%; improve the quality of aquatic products; have multiple functions such as disease prevention and disease resistance, can improve the survival rate of fish species by 5-20%, and secondly, wide adaptability, existing aquatic products. The live bacterial preparations were demonstrated in Sichuan, Liaoning, Guangdong and other places, and all showed obvious effects. The main reason is that it is mainly affected by the living environment of aquatic organisms. The influence of external environment on its action is relatively small. At present, there are only a few reports on live bacteria preparations for shrimps and fish at home and abroad. The third is Highly safe, most of the aquatic live bacterial preparations are separated and purified from the micro-system of healthy aquatic animals, and then act on aquatic animals without any harm to aquatic animals, and there will be no residue in water and body. Its function only plays an active role in a certain period of time, after which the aquatic animals return to the relatively stable living bacteria system before using the live bacteria preparation.
2, glycosides
Glucosin is a natural biological substance composed of sugar (≥30%), glycoside (≥30%) and organic acid, and is a brownish yellow, ashless fine crystal. It is insoluble in ether, chloroform, acetone, benzene, petroleum ether and other bulk agents, soluble in warm water, carbon disulfide, ethyl acetate, soluble in aqueous methanol, n-butanol and glacial acetic acid. The glycosides react chemically with acetic anhydride, ammonium molybdate, ferric chloride and vanillin. The active ingredient of glycosides is stable in performance, safe to use, and has no contraindications with other feed additives. The dosage of glycosides in the feed is 200-500g/t, which can completely replace the antibiotic drugs, and has no residue and does not pollute the environment. After feeding, it can significantly enhance the immunity and disease resistance of aquatic animals, promote growth, increase daily weight gain and feed conversion rate, and have anti-stress and anti-oxidation effects. At the same time, it has a comparative effect on intestinal bacterial diseases. Strong preventive effect. According to the test, the quality of aquatic products fed with glycosidic feed additives is improved, which meets the requirements for green production of animal foods, and the social and economic benefits are very significant.
3. Oligosaccharides
An oligosaccharide, also called an oligosaccharide, is a general term for an oligomer having a linear structure in which 2 to 10 glycosyl groups are linked by a glycosidic bond. There are many kinds of oligosaccharides, but currently used as feed additives mainly include isomaltose, isomaltose, isomaltose, fructooligosaccharide, fructose tetrasaccharide, fructose, galactooligosaccharide, and mannooligosaccharide , soybean oligosaccharide, gentian oligosaccharide, xylose oligosaccharide, and the like. Oligosaccharides can selectively promote the proliferation of beneficial bacteria in the gut of aquatic animals. These beneficial bacteria use oligosaccharide fermentation to produce short-chain fatty acids, reduce intestinal pH, inhibit the consumption of nutrients by pathogens, and reduce the production of toxic and pathogenic metabolites, thereby maintaining and enhancing the health of aquatic animals. Certain oligosaccharides can improve the body's immune response to drugs and antigens, and enhance the immunity of aquatic animals. Compared with the live bacterial preparation, the oligosaccharide is more stable, has high tolerance to harsh environmental conditions such as granulation, puffing, oxidation, storage and transportation, can resist the inactivation of gastric acid, and overcomes the live bacteria preparation in the intestine. Determining the defects of planting difficulties. In addition, it is non-toxic and has no side effects. Therefore, although the current annual production efficiency is low and the production is difficult, its development and application prospects in aquatic feed are still very broad.
4, feed enzyme preparation
Feed enzyme preparations are industrial products containing a single enzyme or a mixed enzyme processed by a specific production process. At present, except for phytase, which is a single product, most of the other feed enzyme preparations are composite preparations containing various enzymes. More applications include cellulase, β-glucanase, xylanase, amylase, protease, pectinase, phytase, etc. Some of these enzymes can be secreted by themselves, such as amylase and certain Some proteases; while another part of the aquatic animal itself cannot be secreted, such as cellulase, β-glucanase and xylanase. The enzyme preparation can destroy the plant cell wall and break down the non-starch polysaccharide (NSP), such as cellulose, hemicellulose and pectin, to decompose these unusable polysaccharides into small molecular sugars that can be digested and absorbed. It can expose the nutrients such as starch and protein protected by the cell wall to make it more nutritious. The enzyme preparation can also reduce the adhesion of the sticky chyme caused by soluble NSP, and the enzyme preparation can also destroy the stable phytic acid phosphorus structure and improve the utilization of phosphorus and other nutrients in the feed. There are four main functions in the application of feed enzyme preparations in aquaculture: promoting the feeding and growth of aquatic animals; improving the function of the digestive system and certain anti-inflammatory effects; preventing and slowing the stress response of aquatic animals; improving the feed effect and reducing The amount of nutrients in the excrement.
5, Chinese herbal medicine feed additives
In recent years, Chinese herbal medicine has attracted attention because of its advantages of no drug resistance and drug residues, small side effects, remarkable effects, and abundant resources. Chinese herbal medicine contains nutrients such as protein, amino acid, vitamins, oils, resins, sugars, plant pigments, macro elements and various trace elements. It also contains a large amount of organic acids, alkaloids, polysaccharides, volatile oils, waxes, tannins and some unknowns. Growth-promoting active substance. According to research, Chinese herbal medicine contains a variety of immune active substances. The role of Chinese herbal medicine additives in aquaculture is mainly reflected in the following four aspects: promoting aquatic animals to feed, increasing feed intake; reducing the feed coefficient, increasing the weight gain rate; Disease occurs, increase survival rate; replace some mineral salt additives and vitamin additives.
6, yeast cell wall
Yeast cell wall is a new natural green additive. Its product is egg yellow powder. It is a special by-product of the extraction of soluble substances in the process of draft beer yeast. It is mainly composed of β-glucan, mannooligosaccharide and glycoprotein. And chitin composition, accounting for about 85% of the dry weight of the cell wall. Studies have shown that the yeast cell wall has the function of stimulating and enhancing immunity; maintaining the balance of living bacteria and controlling diseases and other physiological effects. Aquatic animals not only face the stress of water environment changes, but also suffer from a variety of common diseases. Conventional disease control measures are limited, and low-dose yeast cell walls are added to aquatic feed to enhance fish, shrimp, crab, etc. The resistance of various major diseases and environmental changes increases survival. Feeding the yeast cell wall with healthy fish and shrimp can increase the survival rate of seedlings by 20-40% and increase the survival rate of growth season by 10-20%. Therefore, the use of yeast cell wall special feed is considered to be an effective means to strengthen aquatic animals against disease and promote growth.
3. Prospects for green aquatic feed additives
In recent years, returning to nature and advocating green have become the trend of people's living consumption. As far as aquatic products are concerned, quantity is no longer the primary problem of people's living needs, and the quality of products has become the key to people's choice of aquatic products. On May 29, 1995, the State Council issued the Regulations on the Administration of Feed and Feed Additives, which enabled China's feed safety management work to enter the track of legal management. The Ministry of Agriculture implemented the implementation of the regulations and increased the feed and feed additives. The investigation and punishment of illegal drugs is used to replace harmful feed additives such as antibiotics. This is of great significance for solving drug residues, protecting the environment and the safety of people's lives and property, and accelerating the export of aquatic products. It is believed that with the steady development of aquaculture and feed industry, the theory of aquatic animal nutrition is constantly expanding, the people's living standards are generally improved, and the safety awareness is continuously enhanced. There will be more green aquatic feed additives that meet the needs of production and life. come out.
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