Diagnosis > Poultry
What are the clinical effects in birdsNormally there are no specific clinical signs of mycotoxicosis in birds. The common signs of ill-heath are characterised by apathy and standing feathers which can be observed when the disease is advanced. However, such symptoms could also be confused with other poultry pathologies. In some cases the effect of mycotoxins are sub-clinical and can cause immunossupression with birds exhibiting lesions from secondary infections such as E. coli for example. Some mycotoxins i.e. aflatoxins and ochratoxins cause reduction of the pigmentation of the beak and feet (Figure 1) in addition to growth retardation.
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Mycotoxins also affect the intestine of birds and animals together with the absorption of nutrients which can result in the presence of non-digested feed in faeces. Renal lesion promoted by ochratoxin, patulin and citrinin could also result in liquid faeces which increases litter moisture and the presence of urates which is characterised by white faeces. Poor litter quality and acidic faeces can cause food pad lesions
What are the effects of mycotoxins on the gastrointestinal and renal tract of poultry ?
Following ingestion of mycotoxin-contaminated feed, the intestine and intestinal epithelial cell layer could be exposed to high concentrations of theses metabolites. Some toxins, such as trichothecenes, and especially T2 have a topic effect on these cells causing necrosis. DON, ochratoxin A and patulin can also affect the electrical resistance between the intestinal cell layers. All of these events could be clinically represented by enteritis that can be more severe when associated with bacteria. Microscopic lesions are characterised by reduced villus height and on electronic scanning microscopy the extrusion of the villus tip is observed (Figure 2). In the gizzard, ciclopizonic acid is known as a potent inductor of necrosis and erosions (Figure 3).
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The majority of fungal toxins are lipo-soluble and are quickly absorbed by intestinal cells within the bird. Once absorbed, they travel to the liver and systemic blood circulation through the portal blood supply. These lipo-soluble toxins could also affect the liver in some way. Aflatoxin, in particular, could cause severe hepatic lesions and as a result could cause hamorrhagic lesions on muscles and ascites. The liver can be enlarged and hemorrhagic while the gall bladder may be distended with bile or with chronic exposure, this organ will be pale and friable with a small gall bladder (Figure 4). During chronic exposure, microscopic lesions are described by megalocitosys and vacuolisation of hepatocytes with proliferation of biliary ducts (Figure 5). With ochratoxin (OA) exposure, the lesions are very similar to those observed with aflatoxin but it has a lower LD50 and the most pronounced effect is the severe kidney lesions that are pale, swollen and enlarged (Figure 6). Poor growth, reduced feed efficiency, increased water intake and increased litter moisture are the most important effects of clinical ochratoxicosis. Chickens receiving OA in the diet are less pigmented, and once the OA induces hypocarotenoidemia the effect is more severe than that caused by aflatoxin. The hepatic lesions will also promote increased serum levels of AST and GGt enzymes with a reduction of total proteins and calcium levels in the blood.
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Trichothecenes comprise a vast group of over 100 fungal metabolites with the same basic structure. The mycotoxins T2, DAS and DON or vomitoxin are from the trichothecene group amd ex[psed chickens show oral lesions and decreased feed intake, egg production and eggshell quality. DON and T2 elicit small decreases in hematocrit values, total numbers of white blood cells, including CD4+, CD8+ T lymphocytes and B lymphocytes, and biliary IgA concentrations. DAS has been found to reduce egg production and increase the percentage of thin-shelled eggs in laying hens.
Zearalenone has potent estrogenic properties, can induce signs of oestrus in sows or prepubertal gilts. It can also cause vulvovaginites and reproductive abnormality in the young female but the effect in poultry is not clear. From the literature, zearalenone is described as less toxic than all other mycotoxins for poultry, however the synergic effect of zearalenone with other mycotoxins is not well understood. The detection of this mycotoxin in poultry feed has been suggested to be used as a biomarker for other fusarium toxins (Romer, 1990).
Fumonisins are the most recently discovered group of mycotoxins. Fumonisins have been associated with previously known animal diseases such leucoencephalomalacia, equine and porcine pulmonary oedema. In birds they cause severe diarrhoea, increased liver weight, high mortality and reduced performance. The ergot alkaloids cause ischemia, necrosis and gangrene of limbs. They have recently been observed in sorghum and wheat.
The interaction of mycotoxins in field situations is very common and most mycotoxins behave synergistically. The synergic effect of the interaction of mycotoxins means that lower levels of individual mycotoxins can cause severe problems when occurring with other mycotoxins.
