The word mycotoxin originates from the greek word ‘’Mykes’’ meaning mould while toxicum meaning poison. Mycotoxins are produced by moulds (fungi), these are the secondary metabolites that belong to genera Aspergillus, Fusarium and Penicillium.
By : Dr. Muhammad Ali Tahir, Dr. Asghar Abbas, Dr. Muhammad Asif Raza, Dr. Kashif Hussain
These mycotoxins are present worldwide they are heat stable and lipophilic in nature which means they can combine to lipids and fats or can easily dissolve in them. Mycotoxins cause serious threats to poultry and livestock sector, as they negatively affect various parameters like production, performance and quality.
Aflatoxin (B1, B2, G1, and G2), ochratoxin (Ochratoxin A, OTB, OTC) trichothecenes (DON, T2 toxin, diacetoxyscirpenol), zearalenone, fumonisins and moniliform are different important mycotoxins, and their importance depends upon the level of toxicity and occurrence.
Wheat, maize, barley and peanuts are different sources of mycotoxins. If toxins invade crops before harvesting these are called as field fungi. If it invades post- harvest, they are called storage fungi. Mycotoxins cause heavy economic losses. These are common in tropical and sub-tropical countries in and around Asia.The highest occurring mycotoxin in Asia was FUM (fumonisins), detected in 85% of the samples at an average concentration of 1,354 ppb(parts per billion) .
The highest occurrence of FUM in Asia was detected in a Chinese corn sample (169,500 ppb). DON (deoxynivalenol) prevalence and average concentration in Asia were 77% and 735 ppb, respectively. ZEN (Zearalenone) was the third highest occurring mycotoxin in Asian samples, detected in 49% of tested samples at an average concentration of 201 ppb. In Asia, the highest ZEN value was detected in a Chinese grass sample (8,113 ppb). Aflatoxin was found in 38% of the samples at the highest average concentration worldwide (58 ppb).
The highest worldwide value for aflatoxins was detected in a finished feed sample from Myanmar (10,918 ppb).In Pakistan and India, wideexposure to mycotoxins cause contamination of agriculture commoditieswhich leads to decreased growth rate, feed conversion efficacy, poor carcassyield and carcass quality which ultimately leads to immunosuppression in birds and these birds become highly susceptible to other diseases.
In poultry birds, the harmful effects of mycotoxins cause great economic loss include decreased egg production, poor shell quality, feed refusal, leg weakness, infertility, and toxin residues in meat and eggs. Different permissible levels of mycotoxins are aflatoxins B1 35 ppb, ochratoxins 22 ppb, type A trichothecenes 500, type B trichothecenes 30 ppb, fusaric acid 1000 ppb, fumonisins 1000 ppb, zearalenone group 500.
Prevention and control
Various protocol are followed for screening of mycotoxins for future prevention and control.Scientific knowledge based managemental approach is need of the time for proper mycotoxin screening. In the initial stage there should be routine analysis of feed ingredients stuff for mycotoxin contamination prior to formulation of poultry ration. Moisture and temperature are important factors for the fungal growth, so the humidity should be regulated according to the recommended levels. Bulk storage bins should be well ventilated it should be protected from rain and fluctuation of temperature.
The moisture level of 13% should be adopted. Aflatoxins and other mycotoxins tend to grow at temperatures below 5 to 8 C. Periodic cleaning of all feed handling equipment with 5 to 10% bleach solution can control mold growth. If the feed is stored for a relatively long period, it becomes more susceptible to toxins production so the level, so the level of incidence of toxins increases as the feed is manufactured. The time between feed manufacturing and consumption by birds should be as short as possible. The development of resistant crop strains by both breeding and direct genetic modifications is possible.
Harvesting is an important phase in preventing toxins at various stages of crop growth the best approach is when the crop cycle is completed then harvesting of the crop should be started. Pre harvest practically seem difficult, but it controls measures included prevention by insect infestation and are the major problems in the pre harvest which is practically difficult to control but prevention like crop rotation, proper irrigation and improvement in soil condition are the various measures..
Inpost-harvestcrop management various physical methods being used which includecleaning, dehulling, sieving, separation/segregation of contaminated grains by using ultraviolet (UV) or gamma radiation, density segregation,mechanical separation, solvent extraction and use of antimycotic agents’ Chemical methods include treatment of feed with ozone(ozoniation), ammoniation, use of acids alkalis, aldehydes (structural degradation) and sodium hydroxide. Biological methodsinclude use of probiotics against mycotoxins in feed.
Detoxification and ameliorative methods are very important in this aspect because the mycotoxins contamination is usually unavoidable in nature. Detoxification process removes the toxins and retain the nutritive value of crops without altering its originality. On the other hand ameliorative method is biological inactivation of mycotoxins but different binding agents Ameliorative methods mean biological inactivation by different binding agents such as activated charcoal, bentonites and bovine serum albumin
Use of probiotics
The use of probiotics is very necessary to preserve the normal gut environment.Probiotics form a chelated complex with mycotoxins and prevent its absorption by the body. Probiotic bacteria ‘’Lactobacillus rhamnosus’’ and ‘Nocardia corynebacteroides are used to reduce lesions caused by aflatoxins.Gut mycotoxin exposure can cause oxidative damage to cell membranes and reductions in cellular protein synthesis, which can further produce lesions in various parts of the gastrointestinal tract.
Wide research has shown that exposure to Fusarium damages the gut tissue and reduces nutrient digestion. This can result in necrosis, gizzard erosion, hemorrhaging and malabsorption of nutrients. Physically, the economic loss includes increase in the feed conversion rate (FCR), reduction in performance, watery faeces indicative of poorly digested feed particles.
The mycotoxins damage whole of GIT tract starting form mouth where the mucosal membranes become inflamed and holding capacity and grinding ability of feed is adversely affected when the bird is fed whole grain diet. Development of such lesions expose chickens to higher level of pathogens these lesions cause pain and limit feed intake, reducing the ability of the birds to exploit its genetic capability and production performance.
Different diagnostic methods in laboratories which are commonly implicated are the use of microcolumns, thin chromatography, ELISA (Enzyme linked Immunosorbent Assay), HPLC (High Performance Liquid Chromatography), gas chromatography and, tandem gas chromatography.
Authors :Dr. Muhammad Ali Tahir, Dr. Asghar Abbas, Dr. Muhammad Asif Raza, Dr. Kashif Hussain
Faculty of Veterinary and Animal Sciences
MNS- Agriculture University, Multan