It’s common for mildew to contaminate feed, mildew is everywhere, we can say all feed can be as existed environment for mildew, according to the un fao estimates, more than 25% food and feed were contaminated by mildew in global each year. with development of feed industry, in process of production, stock, sell, a large number of feed products and feed material are easy to be contaminated by mildew, then cause mold. so the problem that feed was mold and mycotoxin contamination can not be ignored in the feed industry and livestock production. as we all known, mycotoxins are harmful to humans and animals. after feed contaminated by mildew, it will cause two hazards: one is that mildew will cause deterioration of feed, feed which was contaminated by mildew, its feed nutrition will be reduced, then cause huge economic losses; second is that after feed was contaminated by mildew, except make livestock poisoning to dead by mycotoxins, the more serious is to reduce immunity system and production performance of livestock and poultry, long-term sub-health state, cause many immunity failure and serious disease which frequently happen and difficult to control, meanwhile it is harm to human health through meat, eggs, milk etc other food chain.  

generally speaking, this problem is serious in the countries and regions with higher average annual temperature, especially developing country in tropical and subtropical, because these countries often lack adequate drying, storage of feed and feed ingredients of facilities and equipment, and high temperature, high humidity climates in tropical and subtropical but also conducive to mold growth and toxin production. thus, feedmill and researchers at home and abroad, attach great importance to mildew, mold removal measures, research and application.

1、common mycotoxins in feed

so far, mildew contamination in feed is almost 100%, bacterial carrier is more than 50% compared with national standard. it mainly exists 6 kinds of toxins, that is aflatoxin, vomitoxin(don), t-2 toxin, zearalenone, fumonisins and ochratoxin, the most hazards for pigs are aflatoxin, zearalenone and don. wang ruojun etc (2003) have been investigated samples of corn, complete feed, protein feed from 13 provinces, it’s found that inspection rate of 6 kinds of mycotoxins in compete feed(aflatoxin, t-2 toxin, don, zon, ocharatoxin, fumonisin) are all more than 90%, especially inspection rate of aflatoxin, t-2 toxin, don and zon is as much as 100%; inspection rate of aflatoxin in protein feed is as much as 100%, others are all above 70%, and there are different levels of overweight; inspection rate of don and zon in corn sample is as much as 100%, and there are different levels of overweight.

1.1 aflatoxin

aflatoxin is a hazard especially big strong carcinogen in humans mainly produced by yellow aspergillus and parasitic aspergillus, which is the most common mycotoxins. aflatoxin was first extracted from moldy peanut powder in1961, after further study found that there were many the derivatives of aflatoxin and similar objects, so it refers to a class of compounds of similar structure instead of a compound. there are four kinds of mycotoxins produced by natural aflatoxin (afb1、afb2、afg1、afg2), in addition there are many kinds of aflatoxin metabolites, heterogeneous and similar objects, such as afm1、afm2、afb2a、afg2a、afbm2a、afgm2a etc, the biggest toxicity is afb1.

the main effects of aflatoxin on animals are tumorigenicity, immune suppression, mutagenicity and degeneration. different animals have different sensitivity to aflatoxin, for example, birds and poultry are particularly sensitive to aflatoxin. the study found, aflatoxin can cause liver damage and lead to the occurrence of liver cancer.

1.2 zearalenone

　　zon is a mycotoxins of non-steroidal and estrogenic activity by fusarium fungi produced by fusarium fungus, and the body has a special affinity estrogen receptors, thus it will affect reproductive performance of animals, lead to infertility, abortion, false heat etc, the emergence of male livestock express female trait.

1.3 t-2 toxin

　　t-2 is one of fusarium fungi, it has main effects on bone marrow, liver, and epithelial lymphocytes etc, it will cause animals loss of appetite or poor feeding, slow response and weight loss and other symptoms, can also cause diarrhea, bleeding spleen, mucous membranes, lymph organs, hematopoietic tissue proposed radioactive damage.

1.4 ochratoxin

ochratoxin is a kind of secondary metabolites with similar structure produced by certain of aspergillus and penicillium species, the strongest toxicity is ochratoxin a. ochratoxin a has strong nephrotoxicity and hepatotoxicity, can cause acute toxic reaction, low intake can cause reproductive performance of chicken.  long-term intake such kind of toxins are carcinogenic. the latest study shows, ochratoxin a has genotoxicity, can increase the likelihood of a cell chromosome breakage.

2、prevention of mycotoxins in feed

so far solving hazards of mildew and mycotoxin for feed, the key point is to deal with anti-mildew and remove mildew. anti-mildew agent is the main measure to reduce pollution of mildew. but anti-mildew agent doesn’t have effect on existed mycotoxins, once mycotoxins have existed, anti-mildew agent is unable to protect animals which fed the feed, thus, it needs to use others measures to degrade toxins in feed, so far, the common measure is to add mycotoxin adsorbent. thus it’s the ideal measure to prevent mildew and mycotoxins in feed through combining anti-mildew agent with remove mycotoxin.

2.1 application of mildewproofing in feed

in recent years, the main measures to anti-mildew in feed are radiation sterilization, add fungicide, use mildew bags, chemical disinfection, and radiation combined with mildew, to control fungal genetic code. so far the main measure to anti-mildew in feed is to add anti-mildew agent in feed. feed anti-mildew agent is a kind of feed additive that can reduce the number of mildew, inhibit mycotoxin, prevent nutrition loss during feed storage, prevent feed mildew and extend storage time. common anti-mildew agent has three kinds, one is organic acids and organic acid salts mildewproofing; second is natural extract mildewproofing; third is others anti-mildew agent.

2.1.1 organic acids and organic acid salts mildewproofing

released by the ministry of agriculture to allow the use of feed fungicide varieties are formic acid, calcium, ammonium formate, acetic acid, sodium diacetate, propionic acid, calcium propionate, sodium propionate, ammonium propionate, butyric acid, lactic acid, benzoic acid , sodium benzoate, sorbic acid, sodium sorbate, potassium sorbate, fumaric acid, etc. these organic acid mildewproofing exists some problems when used alone is antibacterial spectrum narrower, a larger amount of usage, relatively high prices, stringent requirements for mildew conditions. part of organic acid will affect feed nutrition, greater corrosive and irritating, feeding animals residue. thus limited or prohibited by part of countries and areas. so use many kinds of antifungal compound to solve a single fungicide defects. so far compound anti-mildew agent has broader application, it overcomes defects of single anti-mildew, antibacterial wide, good effect on anti-mycotoxin, less effect on feed factor, small usage, low requirement on moisture and acid, non-corrosive and irritating, the defects are antibacterial uneven, high demand on feed mixing uniformity, high price, such as propionic acid and propionate is the most common feed antimildew agent in domestic and international market, is acidic mildew / preservatives, non-toxic to humans, has strong inhibitory effect on various types of mold, bacillus and gram-negative bacteria, no influence on the growth of yeast, still has strong inhibitory effect in high ph. the anti-mildew effect of a mixture of propionic acid and its salts for use in animal feed has been confirmed in long-term practice. they can also be used in conjunction with sodium diacetate to achieve good results. 

2.1.2 natural extract mildewproofing

there are rich plants resources in china, it has huge penitential to develop natural anti-mildew. the study found salvia, ginkgo biloba, skullcap, rosemary, sage, clove, mint, pepper, ginger, sesame seeds, garlic, fennel, pepper, pepper, water weng leather, blackberry lily, licorice extract, eucommia extract has mildew action. among them, allicin can not only kill bacteria, and can effectively kill aspergillus flavus, aspergillus niger, aspergillus fumigatus and other fungi. sun hongxiang (2001) studied minimum inhibitory concentration of mold in feed  of 9 chinese herbs citrus, rugosa, leaves, pepper, chrysanthemum, arrowhead mountain, cinnamon, angelica, fennel, the results showed all have inhibitory effect, and dried tangerine peel, agastache, leaves have a significant antifungal activity. lv wuxing etc (2004) add eucommia extract and propionic acids, organic acids anti-mildew compound tested in corn-soybean meal diet, the results showed three anti-mildew agent had low effect on feed moisture, temperature, while adding eucommia extract in feed can efficiently inhibit growth performance, reduce nutrition loss, and had significant effect on feed appearance, had similar mildew preservation effect with complex organic acids anti-mildew.

　　in recent years, it’s very positive to study and develop bamboo leaves extracts in domestic market. in addition, foreign reports, dry distillation liquid of oak tree, chrysanthemum, maple, cypress, after extracted, it obtains a kind of natural plant resources anti-mildew agent. especially chinese herbs anti-mildew, preservation, more sterilization advantage, no residue, no pollution, abundant resources, low cost, if enhance research and development , it will be prepared the ideal type fungicide.

　　used for anti-mildew in feed, it should be economic green feed additive. in short, it’s the trend that developing natural anti-mildew will replace chemical synthesis mold inhibitor. in recent years, some developed country transfer the point to marine biology for developing new natural mold inhibitor, for example, japan developed a kind of mold inhibitor which use oyster shell as the main ingredient. extracted carapace polysaccharide from crab shell and shrimp shell, that is chitosan, also known as acetyl chitin, is also a natural mold inhibitor, and  as in the sargasso sea, wakame, kelp and other algae, join the potassium iodate, potassium iodide, calcium iodate, mixing into a kind of special compound mould inhibitor. 

2.1.3 others mildewproofing

lysozyme( widely used in albumen of birds, poultry and plasma, urine, tears, saliva, breast milk, placenta, and internal body fluids or tissues inside the cell of the mammalian, among them, the richest in albumen is protamine( around 3.5%), protamine is a kind of basic protein, primarily as a fish (such as salmon, trout, herring, etc.) mature sperm nucleus and dna binding of nuclear protamine exist, such as polylysine research and development as a new generation mold inhibitor it has been expanded.

2.1.4 problems should be paid attention during application of mold inhibitor

　　fao/who has strict demand on mold inhibitor: 1. inclusion rate of mold inhibitor should be smaller, non-toxicity and non-irritating; 2. can dissolved to efficient concentration; 3. stable nature, no change in storage, no reaction with feed or others ingredients; 4. no odor; 5. a wide inhibitory spectrum. with the above points are relatively good mold inhibitor. in the effective dosage of feed mold inhibitor, it cann’t cause the animal to acute and chronic poisoning and drug residues in ultra-limited; there should be no carcinogenic, teratogenic and mutagenic and other adverse effects.

　　the effect of using alone mold inhibitor in feed is usually not good effect, because any mold inhibitor mechanism is much single, only has effect on fixed mycotoxins, while there is no good effect on others mycotoxins, and such special effects affected by the environment relatively large, while feed is a mixture with many the raw material, wherein contains a variety of molds and yeasts, fodder moisture and mildew density are inconsistent, therefore, often using a variety of mold inhibitor complex with of approach to solve single mold inhibitor of defects.

2.2 detoxification methods in feed

　　detoxification methods in feed were mainly physical detoxification, chemical detoxification, enzymatic method, physical adsorption method. (chen xue feng etc, 2007)

2.2.1 physical and chemical detoxification methods detoxification

　　physical detoxification method mainly contains washing method, culling, degermed detoxification method, solvent extraction, heating to poison, radiation, etc. chemical detoxification method mainly contains alkali or oxidant detoxification treatment. the above detoxification methods, in the practical application and the current feed industry, aquaculture are not applicable, because the operation is not only difficult, and can not be in the feed lot, effective and low cost implementation.

2.2.2 enzymatic method

　　enzymatic method mainly choose some enzyme, using its degradation, so that mycotoxins destroy or reduce the toxicity. compared with physical method and chemical method, enzymatic degradation treatment method has less losses and the impact on the nutritional composition, but in practical application, there are still existing many problems, one is that enzymes are not heat , it’s easy to inactivated at high temperature, the production pressing process of finished feed pellets is particularly required high temperature; second is high cost of using enzymatic detoxification method, hard to accept; third is that in the use of enzymatic degradation toxic mycotoxins, some mycotoxins needed complete enzymes, that can completely degrade toxicity, such as in the use of degrading zon( f-2 toxin), part of enzyme only transfer it into another material, the transferred material is still with toxicity, it needs a series of enzyme to completely degrade into non-toxicity material, however, the series of enzyme are still developing.

2.2.3 physical adsorption method

so far physical adsorption method is the general used method. physical adsorption method is a kind of detoxification method that add material in feed that can adsorb mycotoxins, make toxins not adsorbed by animals in animal intestinal, expelled to outside of animals. this kind of method is more feasible method until now, it’s a more feasible common, convenient, efficient detoxification method for feedmill and farm. but need to pay attention to the selection of the adsorbent, according to the actual situation to choose a adsorbent with highly efficient, practical, low price, no negative effect.

at present in the feed industry is mainly used for physical adsorption material in the aluminum silicate class mycotoxins adsorbent. natural aluminum silicate, such as zeolite, diatomite, kaolinite, bentonite etc, because of larger surface area and ion adsorption capacity, has a certain adsorption capacity on mycotoxin, so attract interest of researchers. studies have shown that bentonite can stop adsorption of t-2 toxin in mice small intestinal, increase its excretion from feces, adding 5% bentonite in feed can eliminate the phenomenon of  animal growth inhibition and refused to feed caused by t-2 toxin. however, natural aluminum silicate mineral material has low adsorption capacity, low effective, capture feed volume, has a certain adsorption on nutrition, so no good effect on applying on feed directly. after modified natural aluminum silicate can improve its ability to selectively adsorb mycotoxins. for example, extracted hydrated sodium calcium aluminosilicate from zeolite has better selectively adsorption capacity on aflatoxin b1. but studies shown that hscas is limited to adsorb zon, has poor detoxification effect on ochratoxin a, t-2 toxin etc. with the mycotoxin-depth study in recent years found that montmorillonite (hscas) apply more as a mycotoxin adsorbent in the feed industry and aquaculture, the effect is better.

　the study found that montmorillonite has special structure property, make montmorillonite have strong adsorption property. particularly montmorillonite have selective adsorption priority on polar, unsaturated, easy polar molecule.many mycotoxins such as molecule structure of afb, zon etc contains polar group, such as -oh, c=o-nh2 or containing polarized groups: c=c, c6h5 etc, can occur strongly adsorption effect on montmorillonite surface, therefore montmorillonite is widely used for adsorbing mycotoxins.  many studies shown that montmorillonite has strong adsorption effect on aflatoxin b1, with increasing of aflatoxin b1 content, adsorption increase, both linearly related. study found that adding 0.5% montmorillonite in diet with aflatoxin 3 mg/kg can eliminate production property and related influence of the enzyme activity of the blood of hog which caused by aflatoxin; adding 0.5% montmorillonite in diet with 500 μg/kg and 800 μg/kg can significantly reduce negative effect on weaned piglets by aflatoxin.

mechanism of montmorillonite adsorption on mycotoxin, it is generally recognized that montmorillonite adsorbed mycotoxins and formed stable complex, prevent mycotoxins in animal gastrointestinal absorption, and thus reduce the amount of toxins into the animal body, make its toxicity reduced or eliminated. charcoal and montmorillonite can be combined with mycotoxins in vitro, but only the montmorillonite can adsorb mycotoxins in the body. the data shows, layered aluminosilicate minerals showed that it had higher adsorption efficiency and stability on aflatoxin.

at the same time, montmorillonite has pharmaceutical value, it has been recorded in the european pharmacopoeia, united states pharmacopoeia, british pharmacopoeia and pharmacopoeia of china. study shown that because of protective effect on intestinal mucosa and adsorption effect on bacterial, virus, thyroid hormone , cholic acid salt , bacterial toxins of montmorillonite, this make it a good choice on piglets diarrhea, especially infective diarrhea.

2.3 a new feed detoxification agent

　　natamycin is also known as pimaricin, is a kind of important polyene antibiotics. the antibiotic is a very strong antifungal agents, can obligate yeast and mould, prevent the formation of aflatoxin forming in filamentous fungi. compared with others antibiotics, natamycin has low toxicity on mammalian cell, can widely used in diseases caused by fungus. us fda suggest natamycin is antibiotic used as food additive, also be categorized as gras products. in 1996, food additive committee in our country, evaluated natamycin and suggested to approved, now has listed it into food additive standard, the name of commodity is mei ke （natamaxintm).

natamycin has a certain thermal processing capacity, respectively stable in dry state, short high temperature resistant(100 degree); natamycin is sensitive to fungus, trace use can play a role, as the dosage of the preservative only 1/50 ~ 1/100 for potassium sorbate. and ph range is wide, ph within 3 ~ 9 is active. study shows that it can directly add into yogurt etc fermented product, only inhibit molds and yeasts, no effect on bacterial in yogurt(bifidobacterium), while others preservative has no this function. qi shan reported the application of natamycin on poultry breeding, adding efficient dosage natamycin in feed, water and environment, can control and cure poultry diseases caused by yeasts and molds, no natamycin residues in poultry body.

3、conclusion

so far, the key points in feedmill and farm are anti-mycotoxin, remove mycotoxin, kill mycotoxin. among feed additives, mildew inhibitor role is to prevent mold growth in feed, and prevent loss of nutrients and production of feed mycotoxins; while mycotoxin adsorbent role is to adsorb existed mycotoxins, expel to outside of body, prevent animals adsorbing these toxins, at the same time, adding detoxification agent, such as natamycin etc, can inhibit and kill mycotoxins in feed and animals’ body and adsorbed mycotoxins. therefore, in the measures of prevention and control of mycotoxin hazards, it can achieve ideal effect by using mildewproof, mycotoxin adsorbed and detoxification measures together.  on the one hand, we feed workers and farmers need to do further research on the nature and function of some mould inhibitor and adsorbent, so that developed some strong function, wide range, low cost and efficient product; on the other hand,  need to study how to economic, effective, favorable and safety use the measures of mildew proof, mycotoxin removal, detoxification , opened up a new way to solve the problem of feed mildew.

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