Antibiotics once played a huge role in animal feeding. The rise of antibiotic industry has greatly promoted the development of animal husbandry. Especially in some developing countries, the application of antibiotics in animal husbandry is more common due to the poorer feeding environment. However, a large number of studies have shown that long-term and large-scale application of antibiotics can cause drug resistance in harmful strains and drug residues in animal products. After a person has eaten an animal product with antibiotic residues, physical health will be seriously harmed. With the improvement of human living standards and the emphasis on health, the prohibition of the use of antibiotic additives in animal husbandry production is increasing, and the development of antibiotic substitutes is more urgent.
1 Antibiotic substitutes and effects
1.1 Enzyme preparation
Enzyme preparation is a substitute for antibiotics that has been researched at home and abroad, with mature technology and good use effect. Enzyme preparations have developed rapidly in foreign countries, especially in recent years, the application of protein engineering, genetic engineering and other new technologies in this field has promoted its rapid development. China's enzyme preparation industry started late, but it has developed rapidly. Since the establishment of the first enzyme preparation factory in Wuxi in 1965, after more than 30 years of hard work, our country's enzyme preparation products have continuously increased and the quality has been continuously improved. There are hundreds of products such as amylase, β-amylase, protease, lipase, cellulase, pectinase, β-glucanase, mannase, and phytase.
At present, most researchers believe that the role of enzyme preparations mainly in the following points: 1. The deficiency of supplemental endogenous enzyme activity has disadvantages such as lack of digestive tract enzymes and low activity in young animals. Adding enzyme preparations can effectively compensate for the adverse effects of enzyme deficiency and low activity; 2. Reduce or eliminate anti-nutritional factors in feeds; 3. Reduce the viscosity of digestive chyme, increase the effective absorption area of ​​intestinal wall, and promote the contact and absorption rate of nutrients and digestive tract mucosa; 4. Change the distribution of intestinal flora.
Researchers at home and abroad believe that the addition of enzyme preparations to feeds can significantly increase the animal's daily gain, feed utilization, and reduce the diarrhea rate and mortality of young animals. Selinger (1995) reported that feed enzyme preparations can reduce the rate of diarrhea in piglets by 80%. Zhang Ailing et al. (2001) used a compound enzyme preparation containing protease, amylase, xylanase, and cellulase, and a compound enzyme preparation mainly containing xylanase and cellulase to add 0.1% to piglets. Grain. The test results showed that the two experimental groups had an increase of 12.9% (P<0.05) and 7.55% (P>0.05) of daily weight gain compared with the control group; the rate of diarrhea was reduced by 26.85% and 11.26%. %. Feed enzyme preparations can effectively reduce the viscosity of chyme and increase feed utilization. Han Zhengkang (1996) reported that enzyme preparations can reduce the viscosity of pig intestine chyme by 50% to 80%. Increased utilization of feed nutrients can increase protein digestibility by 6.21% to 20.5% and increase absorption by 21%. Wang Zongpei et al. (2001) added non-starch polysaccharide enzymes to growing barley diets. The test results show that the utilization rate of barley and other energy feeds and the amount added in feed can be significantly improved. Mu Yuelin et al. (2001) reported that adding phytase to laying hens' diets increased the utilization of organic phosphorus, completely replaced inorganic phosphorus, and improved egg production performance. The addition of enzyme preparations can act as some of the hormones in the body. Yu Tao et al. (1996) reported that the addition of enzyme preparations in diets of barley-based chicks can act as thyrotropin-releasing hormone (TRH)-like physiological effects and promote the secretion of T3. Liu Yanqiang et al. (1998) reported that enzyme preparations have the effect of lowering blood glucagon concentrations and increasing blood growth hormone (GH) and insulin-like growth factor (IGF-I).
1.2 Prebiotics
Probiotics are also known as probiotics, live bacteria preparations, probiotics or microbial preparations. The earlier concept of probiotics was that a cultured, living microbe that entered the animal could improve the balance of the gut flora and produce a beneficial effect on the host. The current concept is that probiotics should enter the digestive tract of animals and live there, produce enzymes, inhibit the growth of harmful bacteria, in order to improve the health of the host. At present, probiotics have been produced and applied in large quantities in more than 60 countries in the European Union, the United States, Japan, and Brazil. In the United States, annual usage is 8 000 tons, and in Japan it is around 1 000 tons. It is mainly used for feed additives for pigs and chickens. China's microecological preparations started in the early 1980s but developed rapidly. In 1992, the China Micro-ecological Association was established to include research on forage micro-ecological preparations and applied technologies in the national "Eighth Five-Year Plan" research project.
Probiotics inhibit the growth of harmful microorganisms by competing for nutrients with harmful bacteria in the digestive tract. Stars (1993) reported that probiotics inhibit the growth of Salmonella. K. The BH (1992) study concluded that probiotics have a significant effect on the environment in the digestive tract. Shi Baoming et al. (2000) added probiotics to the diets of piglets. Tests showed that there were a large number of beneficial bacteria in the intestine of piglets, the in vivo environment was significantly improved, the destruction of the intestinal wall was reduced, the utilization of nutrients was improved, and the rate of diarrhea was increased. reduce. Probiotics produce enzymes and increase endogenous enzyme activity in animals. Some researchers believe that most Bacillus can produce protease, amylase, xylan cheese and pectinase. Austin et al. (2000) reported that the addition of probiotics to piglet diets significantly increased intestinal xylanase, pectinase, protease and amylase activity. Probiotics inhibit harmful bacteria and eliminate toxins, which can prevent the absorption of antigens and enhance cellular immunity and body immunity. At the same time, increase the level of antibodies and macrophage activity, and enhance the host's immune function.
A large number of test results have shown that the addition of probiotics to the feed of pigs and chickens can achieve the same effect without or with minimal use of antibiotics.
1.3 Acidifiers
As early as the 1960s, the United Kingdom added organic acids to piglet feed to reduce harmful bacteria and promote piglet growth. Since then, more studies have been conducted in several countries in Europe, mainly on single acids such as organic acids and inorganic acids, and have achieved certain results. However, these single acids have the disadvantages of high cost, poor palatability, toxic side effects, uncontrolled acid strength, and low acidification effects. In the 1990s, some complex acidifiers were studied. And it shows great advantages, and it has the advantages of small dosage, low cost, good acidification effect, safety, wide range of action, etc. compared with single acidifier.
The specific mechanism of action of acidifiers is currently not fully understood. However, most researchers believe that acidifiers mainly provide an acidic environment for the digestive tract. Maintaining a certain pH value in the digestive tract is a necessary condition for enzyme activity, microbial growth, and digestion of nutrients. However, for young animals, the digestive tract oxyntic acid system is not perfect, and the maintenance of the pH value in the digestive tract is largely influenced by the external acid. Zheng Dezhi (1999) reported that adding a compound acidifier to the feed of piglets can significantly reduce intestinal pH and inhibit the growth of harmful microorganisms. Scipinaic et al. (1979) reported that the addition of citric acid reduced the number of E. coli in the stomach, colon and rectum by 38.1, 62.5, and 66.7%. Cao Guowen (1992) reported adding 0 to piglet diets. L% citric acid can reduce E. coli and enterococci by 10.2% and 68.8%, respectively, and the beneficial bacteria lactic acid bacteria and yeast increased by 5.1% and 29.5%, respectively. In addition acidifiers can improve feed efficiency and promote animal growth. Zheng Jianhua et al. (1994) reported that the addition of calcium formate to piglet diets increased protein and energy digestibility by 10.3% and 9.8%, respectively. Li Defa et al. (1993) reported that adding citric acid to the feed of piglets can increase the utilization of feed nitrogen. Some researchers believe that the acidifier can improve the body's immunity, such as citric acid, fumaric acid and other organic acids have the role of promoting antibody synthesis. Acidifiers can also play an important role in the resistance to heat stress. Most of the organic acids can act on the nerve center and reduce the activity. In addition, it can relieve the alkalosis caused by excessive exhalation of carbon dioxide during heat stress.
1.4 Prebiotics
Prebiotics, also known as chemical probiotics, mainly refer to some oligosaccharides and oligosaccharides. Probiotics were originally applied to human health foods. In recent years, a probiotic source added to animal feeds has been successively developed. Currently used species are alpha-glucosyl oligosaccharides, beta-glucosyloligosaccharides, alpha-galacto-oligosaccharides, beta-galacto-oligosaccharides, fructooligosaccharides, mannooligosaccharides, xylans, arabinans, galactosides, and the like. .
The oligosaccharide itself is not a nutrient required by the animal body (except for ruminants), so the oligosaccharides are not digested and absorbed by the passive body or are only slightly digested. Therefore, the role of oligosaccharides mainly in the improvement of the digestive tract environment. It has been reported that oligosaccharides promote the growth and reproduction of beneficial microorganisms in the intestine, and stabilize the obvious role of microflora. Ammerman et al. (1998) and WaldrouP et al. (1993) reported that oligosaccharides reduce the effects of Salmonella and E. coli in the gut. Drink in chicks
The addition of mannose oligosaccharides or lactose in water reduces the proliferation of Salmonella in the small intestine. Zhang Yuntao et al. (1999) added 0.1% and 0.5% zymosan to chicken drinking water respectively. The test results showed that E. coli and Salmonella in the cecum of chickens were reduced by 19.32 and 19.21, respectively (P<0. 01) and 28.60, 29.20% (P<O.01). Moreover, as the amount of added oligosaccharides increases its reduction effect increases. Mirelman (1980) reported that the interception rate of mannan to E. coli was 45% and that of Aeromonas salmonella was 71.4%, while the interception rate for Salmonella enteritidis and Proteus mobilis was 100%.
The improvement of the intestinal environment by probiotics is conducive to the digestion and absorption of nutrients and promotes the growth and health of animals. Farnworth et al. (1992) reported that the addition of oligosaccharides to piglets diets significantly increased daily gains. Alltech (1994) added 0.2% mannose oligosaccharides to chicken diets. The test results showed that the chickens' daily gain and feed efficiency can be improved. It has been reported that the addition of oligosaccharides to the diet of pregnant sows has the effect of increasing litter size and survival rate of piglets.
Betaine
Betaine chemical name is also known as trimethyl amino ethyl lactone. Contains three active methyl groups and can act as a methyl donor under certain conditions. Especially when the methyl group in the feed is accepted by the cysteine ​​and causes methionine deficiency, betaine can be used as a supplement to methionine. In the animal's liver, the methyl group provided by betaine can promote the metabolism of fat, strengthen the role of S-adenosyl methionine, promote the synthesis of choline, and prevent fatty liver. Some researchers believe that the efficiency of methylation by betaine is 2.3 times that of choline chloride (50%) and 3.8 times that of methionine. Generally, 1 kg of betaine can replace 2 to 3 kg of methionine. The results of Rumsey (1998) showed that half of the rainbow trout choline requirement can be completely replaced with betaine. Betaine has a lure effect, can improve feed palatability, improve animal feed intake, and promote digestion and absorption of nutrients. Foreign data show that the addition of 0.5% to 1.5% of betaine has a strong stimulating effect on the sense of smell and taste of all crustaceans such as fish and shrimps. In addition, betaine has the function of regulating osmotic pressure. Some researchers believe that betaine is a buffer material for osmotic shock and can prevent the loss of cell water and the entry of salts under conditions of drought, high humidity, high salt, and high permeability. It plays an important role in maintaining the osmotic pressure of young animals, animals under heat stress, and aquatic animals.
l. 6 Chinese herbal medicine preparation
Chinese herbal medicine research and development is mainly in human medicine. At present, some domestic researchers have turned their attention to the research on animal herbal feed additives. Moreover, animal experiments have shown that Chinese herbal medicines have the effects of promoting growth, improving the health of animals, and improving feed utilization.
The development of Chinese herbal medicine preparations is still in its infancy. The production technology is not perfect. Most of the products produced are crude products with unstable effects. Some of the preparations still have toxic and side effects; the compatibility characteristics are not clear; the processing cost is high. However, Chinese herbal medicines are rich in resources, easy to use, and have rich experience in Chinese herbal medicine application. The development of Chinese herbal preparations has great potential in China.
2 Problems with antibiotic substitutes
2. l Incomplete technology
There are still imperfections at various stages of product development, analysis, and testing. In the production of enzyme preparations and probiotics, there is poor adaptability of strains, low enzyme production, low stability, incomplete detoxification treatment, etc.; determination of enzyme activity, viable counts of probiotics, and types of bacteria are not yet available. Uniform analysis of methodological standards and product quality standards, product quality is difficult to guarantee.
2.2 Low adaptability to feed processing conditions
The weak points of enzyme preparations and probiotics are poor thermal stability and they are easily inactivated. Whether it is heat treatment such as quenching, pelleting or puffing, or long-term storage at room temperature, it will cause inactivation. Some researchers believe that the use of carrier adsorption and embedding process can make the enzyme tolerate 75 ~ 85 °C high temperature granulation, and its enzyme activity can be maintained at more than 70% level. However, this requires a high level of carrier. It is necessary to maintain its own stability while ensuring that it does not damage or damage the enzyme preparation. At present, there are disadvantages such as low carrier adsorption capacity, poor specificity of adsorption, and large damage to additives.
2.3 Consumption of Nutrients in Feed
The role of beneficial bacteria in sustaining their own growth and competing with harmful bacteria in animals requires the consumption of nutrients. At present, there is a lack of consideration in this regard when selecting strains, which results in a large consumption of trace components (soluble amino acids, vitamins, trace elements, and beneficial factors) in the feed. In addition, some carriers (eg, carriers of complex acidifiers) can also adsorb nutrients in feeds.
2.4 Application Limitations and Effect Uncertainties
Compared with antibiotics, its use in young animals and monogastric animals is better, and it is not ideal or effective for adult animals or ruminants, and it has little therapeutic effect on diseased animals. At the same time affected by the external environment, such as dry feed, wet feed or other additive mixed feed, the effect of a larger change.
2.5 High cost
When probiotics are used in feeds, the ratio of addition is 0. l% to 0.2%. At present, the market price of probiotics is around 12 yuan/kg, and the cost per ton of raw materials for use in feeds is increased by about 12 to 24 yuan. However, the addition of common antibiotics costs about 8 yuan per ton of batch material. When using probiotics to completely replace antibiotics, the cost per ton of compounded material increases by more than 4 yuan.
3 Summary
Research and development of antibiotic substitutes have achieved good results and show great potential. However, there are still deficiencies in product production, applications and effects. Improving the unfavorable factors that affect current antibiotic substitutes and developing more desirable alternatives are the work to be done.
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