Mycotoxin Control new insights

The Indian feed and poultry industry is already aware of the possibility of various mycotoxin contaminations of the feed. This holds true not only for mycotoxins like aflatoxins, but to other mycotoxins as well as ochratoxin A, T-2 toxin, zearalenone, citrinin, fumonisins, etc. A number of confirmed and suspected cases of mycotoxicoses in poultry, cattle, pigs have been reported world-wide. These reports represent just the tip of the iceberg. Mycotoxins effects are likely to be subtle and largely go unnoticed unless careful observation is made and detailed records are kept.

Nevertheless, as our industry is geared to maximum performance, factors in the past that have been considered of minor importance to production tend to become increasingly important now. One such factor had been to consider only aflatoxin to be of concern when dealing with mycotoxins in feed. Today, mycotoxins could be a very important factor in tipping the balance from very good to an average production. In other words, the problems associated with fungi growth and various commonly encountered mycotoxins in feed can have serious economic consequences.

The different degrees of toxicity of the individual mycotoxins on the various animal species, such as poultry, cattle and swine are revealed through the corresponding LD 50 values, their influence on health status and economical parameters. What are the possibilities to prevent mycotoxins and to avoid the impairment of animal health and animal performance, if feed is already contaminated with mycotoxins?

The negative influence of mycotoxins has been in existence since the world began. Only since the technological and analytic development of the industry has become so scientific, that mycotoxins could be differentiated and analyzed, the awareness of this problem arose. Nowadays we know that the problem with mycotoxins is widespread. Fungal growth and mycotoxin production depend on a complex interaction of parameters such as temperature, pH value, water activity, oxygen and carbon dioxide levels, composition of the substrate, competitive microorganism, and prevalence of various fungal strains. During the storage of grain and feedstuffs the knowledge of these ecological factors is important to avoid mycotoxin formation as shown in Figure1.

Fig. 1.Ecological parameters that influence fungal growth and toxin production.

Mycotoxicoses are diseases of man or animal originating from mycotoxins. They can be acute or chronic. However, it is not always easy to diagnose mycotoxicoses, because signs of the toxic syndromes are similar to numerous other diseases.

Concerning mycological examinations NEUHOLD (1982) stated, that despite negative findings, feed can be contaminated with mycotoxins. As they are relatively stable chemical compounds, they may persist in contaminated feeds and foods after viable moulds can no longer be isolated (PECKHAM, 1978). Further, mycotoxins which are chemically modified due to interactions between the plant, micro-organisms and mycotoxin producing fungi, cannot be determined by the usual methods of analysis. Therefore, they are called masked mycotoxins. During digestion, however, these masked mycotoxins are easily liberated and are harmful to the animal (GAREIS, 1994). This is another reason why the result of a mycotoxin analysis should only be considered as an indication for mycotoxin contamination.

Acute mycotoxicoses result in striking effects and often death. Fortunately, however, contamination levels in feed are usually not high enough to cause clear-cut toxicoses. Low levels of toxins in feeds are likely to cause an array of metabolic disturbances - see Table 1 - which may or may not be accompanied by pathological changes.

Table 1 - Biochemical effects of various mycotoxins

Low levels of mycotoxins predispose infectious diseases through impairment of humoral and cellular immune response and native mechanisms of resistance. The effects on immunity and resistance are often difficult to recognize, because the signs of disease are associated with the infection rather than the toxin that predisposed the animal to infection. This is because the immunosuppressant effect of many mycotoxins occur at much lower levels of intake than the toxins affect production parameters, such as growth rate or egg production. Toxin ingestion can reduce the effectiveness of vaccination programs.

Following Table 3 lists diseases which are known to increase in severity during aflatoxicoses (BRYDEN and BURGESS, 1985) and T-2 toxicoses (BATA, 1993) respectively.

Prevalence of various mycotoxins in poultry feed: Indian perspective

In a five-year period study, Chandrasekaran et al., 2002 assayed 7,173 samples of oil cake, 3,842 samples of complete feed and 2,463 cereals for the presence of Ochratoxin A (OTA), citrinin and aflatoxin. Apart from aflatoxin, Ochratoxin A was also detected in all samples.

In a related study, Murthy et al., 2005 conducted a survey set up by Department of Poultry Science, Veterinary College, Bangalore to study the incidences of aflatoxin, Ochratoxin A, and T-2 toxin in different feed ingredients and finished feeds. The samples were collected from different regions of the country during different climatic conditions. Out of 1968 samples analyzed by TLC (thin layer chromatography), 1648 samples were found to be positive for the presence of either aflatoxin or ochratoxin or T-2 toxin alone or in combination.

The cereals analyzed were mainly maize and broken rice. Cereals contained Aflatoxin (100%), followed by Ochratoxin A (79 %) and T-2 toxin (78%). Cereal by-products analyzed were deoiled rice bran, rice polish and wheat bran. 94% of the samples were positive for aflatoxin followed by ochratoxin (70%) and T-2 toxin (69%). Oilseed meals analyzed were soybean meal/ Full fat soy, sunflower cake/ deoiled, groundnut cake/ extract, rapeseed meal and til cake. Oilseed meals exhibited 87% incidences of Aflatoxin, 69% of T-2 toxin and 49% Ochratoxin A.


Aflatoxins

Of all the mycotoxins that have been identified since 1960, more studies have been reported on aflatoxins than on any of the others. The aflatoxins have attracted the attention of many scientists, probably because of their toxicological characteristics and the fact that they are unavoidable contaminants found in a variety of foods and feeds.

Aspergillus flavus and A. parasiticus not only invade harvested crops, as had been assumed for so long, but under favorable conditions may also grow on crops before harvest. Aflatoxins fluoresce strongly in long-waved ultraviolet light. The symptoms of aflatoxicosis in poultry ranged from none to acute or chronic disease, with diagnostic characteristics which varied with the species of bird, the amount of toxin consumed, and the length of time over which it was ingested.

The most severe spontaneous outbreak of aflatoxicosis in poultry was described by Hamilton in North Carolina, in which 50 % of a flock of laying hens died within 48 h of being fed highly toxic maize (containing 100 ppm aflatoxin) and at the same time a 95 % drop in egg production occurred. The lesions were mainly in the liver, which was pale and had occasional white pinhead-sized foci and petechial hemorrhages, and the gallbladder and bile ducts were distended. Other changes were a paleness of the kidneys and the accumulation of fat in the organs.


Ochratoxins

Ochratoxins are a group of seven compounds. They are isocoumarin derivatives linked with an amide bond to the amino group of L-phenylalanine. Ochratoxin A is the most toxic member of the group, and most of the literature deals with this member. Ochratoxins are produced by strains of Penicillium and Aspergillus. Observations that moulds which produce ochratoxins on occasion can also produce additional mycotoxins such as penicillic acid and citrinin. Furthermore, there is probably synergism between ochratoxin A and penicillic acid or citrinin.

Lesions in acute ochratoxin A poisoning primarily involve the liver and kidney. Ochratoxin poisoning is not recognized as a defined field syndrome in poultry. In day-old chicks, the principal signs were reduced weight gain, emaciation, dehydration, and catarrhal enteritis.

Broiler chickens, fed a diet containing ochratoxin A from hatching until 3 weeks of age, were emaciated, had a decreased growth rate, and were anemic. The packed blood cell volume and hemoglobin were both reduced. Total plasma proteins and lipids including carotenoids decreased while uric acid was increased. Renal clearance was impaired.

Pullets were placed on an ochratoxin-contaminated diet at 14 weeks of age and fed to 1 year of age to observe the toxic effects of ochratoxin on laying hens. The results were delayed sexual maturity, lowered rate of egg production, depressed weight gains, smaller body weights, increased feed consumption with decreased feed efficiency, a dull appearance, and emaciation. Hatchability of the eggs laid by these hens was reduced.


Trichothecenes

The most important fungi which are responsible for the production of trichothecene mycotoxins are the genus Fusarium.T-2 toxin causes neural disturbances in poultry. The most characteristic pathological changes reported are inflammations and necroses of the mucous membranes of the mouth and crop. The most severe lesions are found in the mouth. Further patho-anatomical changes in chicken described are necrotic processes in the digestive tract, especially in the crop and occasionally in the proventriculus and gizzard, and degeneration of liver, kidneys, and myocardium.


Zearalenone

Zearalenone is synthesized by strains of Fusarium. Zearalenone occurs as a natural contaminant in corn, wheat, barley, oats and sorghum. It has been found as an ubiquitous contaminant in corn.


‘ADSORPTION’ of mycotoxins – not effective against all of them!

Different binders, natural, herbal as well as synthetic, are used for this purpose. Such binders have so far been used extensively in feed to control mycotoxins. These binders on one hand have small particles, large surface area but on other side have a very narrow range of mycotoxin binding ability. Moreover, the binding ability is restricted to aflatoxins. Other mycotoxins including zearalenone, T2 toxin and ochratoxin lack the functional polar groups required for efficient adsorption or binding. This feature makes the usage of binders ineffective in controlling mycotoxins.


‘Biotransformation’ of mycotoxins - leading in control

Adsorbents are thus ineffective in controlling commonly encountered mycotoxins. New generation of mycotoxin control in the form of Biotransformation, using microbes to cleave and detoxify mycotoxin molecules, offers a more targeted and safer method of mycotoxin control methods. A safe strain of a bacteria and yeast can detoxify them. This method is time tested and has been in use since many decades to effectively control the perennial problem of mycotoxins in feed.

Many in-vivo tests and successful commercial usage of this patent from Biomin worldwide, confirm the efficacy of Bio-transformation approach to control mycotoxins.