Animal feed, including herbage, may be contaminated with organic and inorganic compounds and with particulates. Organic chemicals comprise the largest group and include plant toxins, mycotoxins, antibiotics, prion proteins, animal toxins and pesticides. Inorganic compounds include heavy metals and radionuclides. Particulates such as weed seeds and certain bacterial pathogens are common contaminants of feed.
The effects of feed contaminants and toxins range from reduced intake to reproductive dysfunction and increased incidence of bacterial diseases. Residues transferred to edible animal products represent another reason for concern. Comprehensive legislation is in place for the control of several of these chemical compounds and pathogens in feed. However, in many developing countries including India, the statutory control of contaminants is at best rudimentary. Fortunately, the chemical nature, mode of action and counteractive measures for many of substances have been well documented but the procedures for total elimination or destruction of toxins are not only cumbersome but also expensive, making them practical. The adequacy of elimination of toxins by breeding strategies may not be compatible with high production. Satisfactory processing is essential for the profitable inclusion of some of the byproducts of novel oil seeds in livestock diets.
Various chemicals were attempted for the removal of toxic components for upgrading the feedstuffs. These methods usually degrade the toxicants but these also cause substantial loss of nutrients through leaching. Moreover, chemical treatments are not used due to environmental concerns. Therefore, the scope for decontamination of feeds is limited and generally uneconomical and prevention is the most effective practical strategy. Detoxification was often achieved but economical feasibility remains questionable in many circumstances. Processing technologies that are economic and practical are urgently required. The alternative is to restrict the level of the inclusion of toxin-containing feedstuffs such that the levels are within tolerable limits.
1 – Mycotoxin formation may occur when the causative fungi grow on crops in the field, at harvest, in storage, or during feed processing; essentially whenever favorable conditions for their formation prevail. Generalizations about geographical distribution of particular types of mycotoxins are difficult due to widespread distribution of the causative fungi. However, aflatoxins and fumonisin tend to prevail in warmer climates, while cooler regions with higher moisture are subject to ochratoxin, zearalenone, vomitoxin (deoxynivalenol, DON), T2 toxin, and others. Each mycotoxin has its own particular effect, and all can be devastating. Co-contamination by one or more types of mycotoxin occurs naturally, and exerts a greater negative impact on health and productivity of livestock than contamination by individual mycotoxins.
The physical effects of mycotoxins range from reduced feed intake and poor feed conversion to a general inability of an animal to thrive. Symptoms vary according to toxin. Vomitoxin, called the feed refusal factor, affects mainly pigs.
Zearalenone affects the reproductive organs of pigs and dairy cattle. Fumonisin causes a nervous disorder in horses due to its impact in the brain. Ochratoxin causes kidney damage. Poultry and pigs are sensitive to ochratoxin, whereas dairy cattle can tolerate higher levels of ochratoxin because of its biotransformation into a nontoxic form by ruminal bacteria. Aflatoxins, the most common mycotoxin, cause increased susceptibility to disease. At the organ or cellular level mycotoxins differ in their effects with severe damage done to the liver and kidney by aflatoxins and on reproductive organs by zearalenone. Other indices of mycotoxicosis include mammary gland swelling and ovarian atrophy (zearalenone), oral lesions in chicks (T2 toxins), nervous system disorders and necrosis of the extremities (ergot alkaloids). Mycotoxins may also impact human health, as many are transferred into milk or meat following ingestion by the animal.
2- For several decades, scientists in the field of vegetable oils tried unsuccessfully to detoxify cottonseed by a practical method. By using 20-30% (by wt) of ethyl alcohol (90% in vol) with commercial hexane as a mixed solvent, we were able to extract effectively both gossypol and oil from cottonseed prepressed cake or flakes. Free gossypol in meal was reduced to ca. 0.013-0.04%; total gossypol was reduced to 0.32-0.55%; residual oil was reduced to ca. 0.5% or less. Any aflatoxin present also can be eliminated by this process. The detoxified cottonseed meal can be used as animal feed. Cottonseed protein can be used to substitute for soy protein. The extracted oil is of better quality than that obtained by the usual hexane extraction method, and gossypol is a valuable byproduct
Because aflatoxin contamination is unavoidable, numerous strategies for their detoxification have been proposed. These include physical methods of separation, thermal inactivation, irradiation, solvent extraction, adsorption from solution, microbial inactivation, and fermentation. Chemical methods of detoxification are also practiced as a major strategy for effective detoxification.
Structural Degradation Following Chemical Treatment:
A diverse group of chemicals has been tested for the ability to degrade and inactivate aflatoxins. A number of these chemicals can react to destroy (or degrade) aflatoxins effectively but most are impractical or potentially unsafe because of the formation of toxic residues or the perturbation of nutrient content and the organoleptic properties of the product. Two chemical approaches to the detoxification of aflatoxins that have received considerable attention are ammoniation and reaction with sodium bisulfite.
Many studies provide evidence that chemical treatment via ammoniation may provide an effective method to detoxify aflatoxin-contaminated corn and other commodities. The mechanism for this action appears to involve hydrolysis of the lactone ring and chemical conversion of the parent compound aflatoxin B1 to numerous products that exhibit greatly decreased toxicity.
On the other hand, sodium bisulfite has been shown to react with aflatoxins (B1, G1 , and M1) under various conditions of temperature, concentration, and time to form water-soluble products.
Modification of Toxicity by Dietary Chemicals:
The toxicity of mycotoxins may be strongly influenced by dietary chemicals that alter the normal responses of mammalian systems to these substances. A variable array of chemical factors, including nutritional components (e.g. dietary protein and fat, vitamins, and trace elements), food and feed additives (e.g. antibiotics and preservatives), as well as other chemical factors may interact with the effects of aflatoxins in animals.
Alteration of Bioavailability by Aflatoxin chemisorbents:
A new approach to the detoxification of aflatoxins is the addition of inorganic sorbent materials, known as chemisorbents, such as hydrated sodium calcium aluminosilicate (HSCAS) to the diet of animals. HSCAS possesses the ability to tightly bind and immobilize aflatoxins in the gastrointestinal tract of animals, resulting in a major reduction in aflatoxin bioavailability.
- A method of detoxifying a fumonisin or a structurally related mycotoxin, present in harvested grain, the method comprising reacting the fumonisin with an enzyme having the structure of the fumonisin degradative enzyme elaborated by Exophiala spinifera, ATCC 74269, Rhinocladiella atrovirens, ATCC 74270, or the bacteπum of ATCC 55552.
- The method of Claim 1 wherein the detoxification reaction occurs during storage of the harvested grain.
- The method of Claim 1 wherein the detoxification reaction occurs during processing of the harvested grain. 4. The method of Claim 1 wherein the detoxification reaction occurs in processed grain which is to be used as animal feed.
- A method of detoxifying a fumonisin, a structurally related mycotoxin, a fumonisin hydrolysis product, or a hydrolysis product of a structurally related mycotoxin, present in harvested grain, the method comprising reacting the hydrolysis product with an APi catabolase elaborated by Exophiala spinifera, ATCC 74269, Rhinocladiella atrovirens, ATCC 74270, or the bacterium of ATCC 55552.
- The method of Claim 5 wherein the detoxification reaction occurs during storage of the harvested grain.
- The method of Claim 5) wherein the detoxification reaction occurs during processing of the harvested grain.
- The method of Claim 5 wherein the detoxification reaction occurs in processed grain which is to be used as animal feed.
- A method for detoxifying, in harvested grain, a fumonisin or a structurally related mycotoxin and for detoxifying a fumomsin hydrolysis product or a hydrolysis product of a structurally related mycotoxin, the method comprising reacting the fumonisin with an enzyme having the structure of the fumonisin degradative enzyme elaborated by Exophiala spimfera, ATCC 74269, Rhinocladiella atrovirens, ATCC 74270, or the bacterium of ATCC 55552, and reacting the hydrolysis product with an APi catabolase elaborated by Exophiala spinifera, ATCC 74269, Rhinocladiella atrovirens, ATCC 74270, or the bacterium of ATCC 55552.
- The method of Claim 9 wherein the detoxification reaction occurs during storage of the harvested grain.
- Nutrition of Chicken by Leeson and Summer.
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- Eaton,D.L. and Groopman,J.D.1994. The Toxicology of Aflatoxins. Academic Press, New York. p383-426.
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Muhammad Nauman Manzoor
M.Sc. (Hons.) Animal Nutrition