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					General Review of Mycotoxins
Dr.Kedar Karki

Mycotoxins
 Mycotoxins are secondary metabolites produced by fungi 




 

present in feed. Mycotoxin's production depends on fungus specie and strand, plant specie, environmental moisture and temperature, presence of pests, etc. Mycotoxins cause damages in feed quality. Their incidence depends on geographical area and season. Mycotoxins are toxic: they produce mycotoxicosis and drop of performance. Their presence in feed can be reduced by applying Hazard Analysis and Critical Control Points.

Mycotoxin toxicity
Main factors that influence toxicity of mycotoxins are:  Bioavailability.  Combined effects between several mycotoxins.  Amount of mycotoxins consumed. Continuous or intermittent ingestion of the contaminated feed.  Animal weight, age, physiological and health status.

Mycotoxicosis
 Mycotoxicosis (1962, Forgacs and Carl): host's

intoxication as a result of ingestion of a toxic substance of fungal origin.Some cases show evident symptoms that can be easily associated to mycotoxicosis.  In the other hand, subclinical mycotoxicosis is only recognizable by drop of performance and health status.  Susceptibility to mycotoxicosis depends on animal specie, age, sex and coexistence with other illness.

Mycotoxicosis can cause:
 NUTRITIONAL  HEALTH ASPECTS  Mycotoxicosis typical

ASPECTS  Feed consume decrease.
 Nutrient absorption

of every mycotoxin.
 Immunosupression:

decrease.

arise of other pathologies.

MYCOTOXINS CLASSIFICATION AND MODE OF ACTION
 Lots of described

mycotoxins.
 Varied molecular weights

and structures: difficult to classify.
 They keep associated to

 Mycotoxins persist in food

chain. fungus or substrate.
 Many of them are stable to

chemical/physical treatments.

Classification according to pathology
Hepatotoxins: sporidesmine, aflatoxins, luteoskirin, cycloclorotin, rubratoxins, sterigmatocistin. Nephrotoxins: ochratoxin, citrinin. Neurotoxins: penitrem A, patulin, fumonisins, citreoviridin. Toxins of intestinal tract: trichotecenes, T-2 toxin, deoxynivalenol (Don, Vomitoxin), HT2 toxin, fusarenone. Steroidal; strogenic (Zearalenone), D vitamin analogous Haemorrhagic and circulatory toxins: Ergot alkaloids, aflatoxins.

Classification according to chemical structure

Chemical structure
 Chemical structure determines:
 Mycotoxin's mode of action.  Mycotoxin's method of detoxification

Chemical structure and mode of action Mode of action:
 specific biochemical interaction through

which a substance produces its biological effect.  In order to achieve a biological effect, an interaction with a receptor is essential.

Chemical structure and mode of action
 Chemical groups of the receptor must

interact with chemical groups of the substance, that is, chemical structures in the binding point must be complementary.

KEY-LOCK MODEL

Mycotoxins with shared chemical structure may interact with the same receptors an thus have an alike biological effect.

Chemical structure and mode of action

 Into practice T2 toxin, HT2 toxin,

deoxynivalenol, nivalenol have a sesquiterpene group in their structure and they all have necrotic effects on mucous membranes.

Chemical structure and mode of action
 B1, B2, G1, G2 aflatoxins,

sterigmatocistin have cumarinic group in their structure and they all have haemorrhagic effects alike anticoagulant active principles used in human pharmacology: warfarine, acenocumarol. These active principles also show a cumarinic structure.

Aflatoxin B1

MYCOTOXIN ANALYSIS IN FEED MANUFACTURING
 Decision making in raw material

purchasing

Usual methods of analysis
 Thin layer Chromatography (TLC).
 Liquid Chromatography (HPLC).  Gas Chromatography-Mass

spectrometry (GC-MS).  Immunoassay(ELISA).

Maximum allowed concentration
 Gradually more countries legislate about mycotoxin limits

in fodder and raw materials destined to animal nutrition. Maximum concentrations are set depending on: Mycotoxin's toxicity Animal specie sensitivity and age Fungi load characteristic of plant specie Availability and limits of analysis method. Maximum concentration for each mycotoxin depends on every country.

 


 

Maximum allowed concentration
 Maximum concentration depends on

animal specie and age and on raw material or fodder.

INTERPRETATION OF RESULTS

 Interpretation of results


  

Considering the results obtained in the lab, decisions are made taking into account: Concentration of each mycotoxin (individual effect). Concentration of all mycotoxins analysed as a whole (combined effects). Possible bias of analysis. Presence of non-analysed mycotoxins.

COMBINED EFFECTS

There are more possibilities of finding combined effects in mycotoxins...
 With similar molecular structure.

Synthesized by the same fungal strand or specie. Synthesized by the same fungal family.

The appearance of combined effects depends on:
 Concentration of each mycotoxin.
 Animal sensitivity (specie, age, health

status).

Additive effect

 Combined effect of A and B mycotoxins

is equal to the addition of the effect of each mycotoxins.

Additive effect
 Aflatoxins + Deoxynivalenol

Poultry: decrease in proventriculus weight, increase of DHL enzyme, indicator of tissue damage.
 Aflatoxins + Cyclopiazonic acid

Poultry: growth decrease. Pigs: feed intake and growth decrease; inflammation and necrosis of the gastrointestinal tract. hepatotoxicity.

Additive effect
 Aflatoxins + Diacetoxyscirpenol

Pig: Weight and growth decrease, alteration of blood parameters that indicates hepathotoxicity.

 Aflatoxins + Moniliformin

Poultry: weight and efficiency decrease. Increase of heart's relative weight. Biochemical parameters indicate nephro and

Additive effect
 Citrinin + ochratoxin A

Pig: nephrotoxicity. They affect transport of several molecules and protein synthesis.
 Fusaric

Poultry: feed consumption and growth decrease. Nephro and cardiotoxicity.
 Ochratoxin A + T-2 toxin

Poultry: Weight decrease, increase of kidney, liver, proventriculus and gizzard relative weight. Nephro and hepatotoxicity.

Additive effect
 Fumonisin B1 + Diacetoxyscirpenol

Turkey: Weight decrease. Hepatotoxicity.

 Fumonisin B1 + T-2 toxin

Poultry: weight and efficiency decrease. Nephro and hepatotoxicity.

 Deoxynivalenol + Moliniformine

Turkey: weight of kidney and heart increases. Tissular damage in myocardium.

Synergic effect


Combined effect of A and B mycotoxins is higher than the addition of the effect of each mycotoxin.

Synergic effect

 Aflatoxins + Ochratoxin A

Poultry: Weight decrease, mortality increase. Hepatotoxicity and severe nephrotoxicity.

 Aflatoxins + Toxin T-2 Very important

because of its prevalence Poultry: weight decrease, increase of kidney, gizzard and heart relative weight; decrease of the medium corpuscular volume and of the potassium plasma levels.

Synergic effect

 Deoxynivalenol + Fumonisin B1

Pigs: great weight decrease.

 Deoxynivalenol + Zearalenone

Pigs: theratogenesis in piglets.

Antagonistic effects

 Combined effect of A and B mycotoxins

is less than the addition of the effect of each mycotoxin. (but higher than the effect of each mycotoxin separately).

Antagonistic effects

 Citrinin + ochratoxin A

Poultry: the presence of these mycotoxins together reduces the toxic effects of the mycotoxins separately (growth and water consumption decrease).

 Aflatoxins + diacetoxyscirpenol

Poultry: the presence of these myocotoxins together reduces the toxic effects of the mycotoxins separately (growth and feed consumption decrease).

BIAS OF THE ANALYTICAL METHOD
 1. Not representative sampling

Sample not representative, because of the big sample size or the king of storage/container of the raw material.
2. Not validated analysis method Analysis method should have been validated by a prestigious institution like International Organization for Standardization (ISO). 3. Low quality standards Trouble to get mycotoxin standards in some countries. % recovery of solid standards by dissolution <100%. Standard solution not stable. 4. Procedure for sample extraction

PRESENCE OF NONANALYSED MYCOTOXINS
 Not-analysed mycotoxins

In raw materials there could be mycotoxins whose are not analysed: 1. WELL-KNOWN MYCOTOXINS Whose analysis is not performed because of economic reasons, lack of validated methods, presence unlikely, etc. 2. LITTLE-KNOWN MYCOTOXINS Mycotoxins whose incidence and effects are little known. THERE ARE MORE THAN 300 DESCRIBED MYCOTOXINS

Reference:
 Interpretation of the results of

mycotoxin's analysis in feed  Author: Paper Presented at Biovet Symposium 2007 (Courtesy of Biovet SA)


				
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karki kedar Dr. karki kedar Dr. poultry Disease consultant
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