Fungi can invade, colonize, and produce toxins either during preharvestor postharvest stages (i.e.storage, transport, and processing). The colonized fungi produce and secrete low-molecular-weight toxic compounds referred as “secondary metabolites” or “mycotoxins,” which are not required for normal growth and survival of fungi. Filamentous fungi adapted to terrestrial environment are recognized as mycotoxin producing fungi. Aflatoxin is most common and naturally occurring mycotoxin produced by the fungus Aspergillusflavus, A. parasiticus and A. nominus. Since, AspergillusSpp. is abundantly present in the nature which infects cereal crops- wheat, walnut, corn, cotton, and peanutsincluding tree nuts.Also, it occurs in many concentrate feed ingredients i.e. soybean, oil cakes (groundnuts, cottonseed, sunflower, palm and copra) and fishmeal that commonly used in the poultry feed, hence it directly affect the health of poultry.
Aflatoxin (AF) can produceits residual effect by passing into the poultry products which may pose threat to human health through their carcinogenic, mutagenic, teratogenic, immunosuppressive and other adverse effects. There are more than 20 AF known amongst them,AF’s of major importance areAF B1, AF B2, AF G1 and AF G2. While AF M1 and M2 mainly occur in milk (small quantities of AF M1 reported in eggs) are the hydroxylated metabolites of AFB1 and AFB2 respectively. AFB1 is commonly encountered and known for its carcinogenic properties is included in Group 1 of carcinogenic agents by the International Agency for Research on Cancer (IARC).
Figure1: Aspergillus flavus in feed
Source: Bhat et al., (2010)
Figure 2: Fungi on a) Ground nut b)Cassava c) Millet
Source: Golob, (2007)
Adverse Effect of Aflatoxicosis on Poultry Health
Growth performance of Broiler
Presence of AF in poultry feed reduces weight gain and feed intake, feed efficiency and consequently growth performance.
In layers, reduction of egg production, egg weight, egg quality and increased mortality of hens is usually observed.
Deterioration of Carcass Quality
There may be abnormal pigmentation and increased bruising, resulting in carcass condemnation and thereby economic losses to farm owners.
Various Visceral organs
Poultry is extremely sensitive to AF as AFB1 is converted into aflatoxin B1-8,9 exo-epoxide (by the action of cytochrome p450 family in liver), which is in turn converted into 8,9-dihydroxy-8-(N7) guanyl-9-hydroxy aflatoxin B1 adduct. This adduct is metabolized into aflatoxin B1 formaminopyrimidine adduct which is mutagenic and carcinogenic.
Ducks are most susceptible species to AF, followed by turkeys, broilers and laying hens. AFBO bind with cellular compounds (proteins, DNA and RNA) to influence normal cellular activities.
Erosion and roughening of the gizzard lining occurs that resultsin decreased absorption of nutrients, stunted growth and nutrient deficiency related syndromes. It also causes reduction in activities of enzymes involved in digestion.
Immunosuppression caused by AF may lead to many disease outbreaksdue to secondary infection, vaccination failures, and poor antibody titers.
Post Mortem Findings in Birds
Post mortem lesions depend on dose of the toxin, species of fungi, type and age of poultry birds infected.Although overall carcass appears emaciated and anaemic, some of the important organs affected, with their respective lesions are mentioned below.
Liver is primary target organ during aflatoxicosis. It becomes swollen, pale or yellow, friable (due to precipitation of fat) and hemorrhagic.A characteristic net like hemorrhagic lesions may be seen on capsular surface. Swelling of gallbladder occurs. Liver fibrosis leading to atrophy may occur during late stages. Ducks, due to their high susceptibility to aflatoxin a potent carcinogenic agent as discussed elsewhere in this context, causes hepatocellular carcinoma.
Figure.1: Fatty and yellowish liver in Aflatoxicosis
PC: Ivan Dinev
Kidney a swollen kidney with deposition of urate crystals is common observation.
Atrophy of bursa of Fabricious, thymus and spleen. This will lead to reduced lymphocyte production and maturation resulting in immunosuppression in birds. Therefore, it increases chances of infectious diseases and reduced performance of bird’s thereby economic losses to farmers.
Skin and Muscle
AF affects clotting factor synthesis, making blood vessels more fragile which produce hemorrhages under the skin, muscles and on internal organs.
History, clinical signs and lesions may suggest the feed intoxication however, moldy feed and feed ingredients give a valuable clue for the diagnosis.
Definitive diagnosis is done by detection and quantification of the aflatoxin in affected feed or dead birds. Necropsy and related diagnostic tests should be done along with feed analysis if aflatoxicosis is suspected. Feed and ingredient samples should be properly collected and submitted for analysis. Multiple samples from different sites which increase the confirmation potential (precision) of aflatoxin in affected feed lot should be collected. Sample of 500 g should be collected and submitted in separate containers. Clean paper bags with proper label are used for sample collection.Cell layer chromatography, gas chromatography or liquid chromatography and mass spectrophotometry are used for analysis of feed for detection toxins.
Treatment of Aflatoxicosis in Poultry
No specific treatment for aflatoxicosis is available. Prevention is the best method to control the aflatoxicosis. Removal and replacement of toxic/contaminated feed is necessary. Along with it unadulterated feed should be fed and standard management practices must be followed viz proper storage of feed under low moisture condition and at low temperature.
Table 1: Maximum Permissible Limit for Aflatoxin in Feed Aflatoxin Levels: in grains, ingredients and poultry feed (FDA, 2011)
Maximum permissible limit for aflatoxins (B1, B2, G1, G2, etc.) in all food commodities in India is 30 ppb (FSSR, 2011).
Prevention and control of Aflatoxin
A) Prevention of mould/fungal growth
In stored grain, mould damage can be prevented mainly by three methods viz. drying of grain, controlled atmosphere storage and chemical treatment as described below.
Drying of Grain
Dry grain can be stored for longer period and it also prevent infestation of insects.Less moisture content is unfavorable for fungal/mould and insect growth. Grain drying under direct sun light is most widely used, cheap and efficient indigenous practice. Other methods for drying include mechanical drying, in-bin, infrared and microwave or sonic drying.
Controlled atmosphere storage
This is done in order to deplete oxygen in feed to such a level at which the microbes and insects cannot grow. Air-tight storage also works on the same phenomenon, where the depletion of oxygen is carried out by manipulating grain respiration, resulting in inhibition of aerobic fungi, elimination of mycotoxin producing fungi. This conserves desirable quality factors in the grain. Natural cooling is another effective method of preserving grain. Low temperature does not allow the thermophillic micro-flora to grow.
B) Control of Aflatoxicosis
Separation of Infected Grains
Physical separation of infected grains is an efficient and feasible method to minimize or avoid further aflatoxin contamination. This can be done either by manual operation or with the help of an electronic sorter. Fungal infection of seeds or grain usually imparts characteristic color or other physical properties.
Cooking at atmospheric pressure destroys 50%of the toxinspresent. Dry roasting and oil roasting of groundnut reduces aflatoxins to a significant degree. Cooking rice under 15 lbs pressure for 5 minutes will destroy maximum (upto 72%) aflatoxins as compared to ordinary cooking. Light can also be used to destroy aflatoxin in crude groundnut oil. Visible light is more effective than either ultra-violet or infra-red light. Gamma irradiation (5-10 Mrad) causes reduction in aflatoxins, however, it cannot completely destroy the toxin and its mutagenicity. The treatment combination of gamma irradiation and ammoniation is used for high degree aflatoxin decontamination. Chemical treatment is used for removal of mycotoxins from contaminated commodities. The chemicals such as acetic acid, ammonia gas, ammonium salts, calcium hydroxide, formaldehyde, hydrogen peroxide, methylamine, ozone gas, phosphoric acid, sodium bicarbonate and sodium bisulfite can be utilized to neutralize aflatoxins in feed.
Prevention by using various adsorbents/ toxin binders in feed
Absorbents and toxin binders are used in order to prevent aflatoxicosis. These substances adsorb and bind the aflatoxins rendering them harmless compounds respectively. Some of the important binders and/ adsorbents are mentioned below.
Sodium bentonite, hydrated sodium calcium aluminosilcate (HSCAS), Bacillus subtilis, Bentonite clay, Berevibacillus laterosporus, Dried banana peel, Lactobacillus monson, Neutral Electrolyzed oxidizing Water (NEW) , Saccharomyces cerevisiae (yeast extract) and selenium. Antioxidant from plant origin i.e.citrus fruit oil, Allium spp (garlic) extract, Curcuma longa(turmeric) extract and awla extract can also be suggested which help to improve health of birds in aflatoxicosis.
Aflatoxin is most common mycotoxin found in poultry feed and ingredients in India which reduces performance and increases disease incidence in poultry birds. Negative effects observed are due to alteration in nutrient intake, absorption, metabolism and immune function. Diagnosis should be based on clinical signs, lesions and isolation and identification of aflatoxin in feed. Aflatoxicosis should be prevented at its primary level and controlled as early as possible so as to avoid further harmful consequences in terms of performance of birds and economic losses to farmers.
1. Division of Pathology, ICAR- Indian Veterinary Research Institute, Izzatnagar
2. Division of Animal Nutrition, ICAR- Indian Veterinary Research Institute, Izzatnagar
Bhat, R., Rai, R. V., & Karim, A. A. (2010). Mycotoxins in food and feed: present status and future concerns. Comprehensive Reviews in Food Science and Food Safety, 9(1), 57-81.
FDA Mycotoxin Regulatory Guidance, August 2011. Available online: https://www.ngfa.org/wpcontent/uploads/ngfacomplianceguidefdaregulatoryguidanceformycotoxins8-2011.pdf (accessed on 02 Feb. 2018)
Food SafetyandStandards (Contaminants, Toxins and Residues) Regulations, 2011 Available online:http://fda.up.nic.in/Legislation/regulations_2011/Food%20safety%20and%20standards%20(contaminats,%20toxins%20and%20residues)%20regulation,%202011.pdf (accessed on 02 Feb. 18)
Golob, P. (2007). On-farm mycotoxin control in food and feed grain (Vol. 1). Food & Agriculture Org.
Ivan Dinev, http://www.thepoultrysite.com/publications/6/diseases-of-poultry/215/aflatoxicosis/ (accessed on 4 Feb 2018)