Fungal contamination of agricultural
products is often unavoidable and of
worldwide concern, because the products
frequently contain toxic metabolites known
as mycotoxins. Mycotoxin contamination
can occur in the crop, during harvest, at
storage, or even after feed manufacturing.
Mycotoxins are fairly stable compounds
that cause a wide variety of deleterious
effects in poultry and other animal species,
depending on the nature and concentration
of toxins in the diet, animal species, age,
and nutritional and health status at the time
of exposure to contaminated feed. Several
factors have an influence on the
development of molds, including the
moisture content of the grain or feed,
environmental humidity and/ temperature,
oxygen concentration, pH, and storage
length. My cotox ins cause toxic,
teratogenic, mutagenic, and carcinogenic
effects, and/or depression of the immune
system. Clinical immunosuppressive
conditions can be confused with those
caused by other pathogens. This is why it is
frequently difficult to establish a precise
differential diagnosis. The fact that a great
variety of mycotoxins affect different organs
in the urinary, digestive, and reproductive
tracts, or the nervous and immune systems,
among others, makes recognizing a
mycotoxicosis condition even harder.
For many years, mycotoxins were studied
individually in each species, without
considering that under field conditions
contamination with only one mycotoxin
normally does not occur. Only recently the
combination effect of several mycotoxins
started to be evaluated.
The scientific community is concerned
about the fact that mycotoxin levels that
used to be considered as safe in the past,
currently have shown their ability to cause
problems when combined with "low" levels
of other mycotoxins. This potentiation of
mycotoxin effects is due to the synergy that
occurs when several mycotoxins are
combined in the feed. One example of
combined contamination in grains and
feeds i s the af latox in- fumonisin
combination. Another example is vomitoxin
and zearalenone, which are naturally found
in combination in the same grain or oil
seeds/meals.
It has been consistently shown that the
immune system is an important target of
mycotoxins, causing adverse effects on the
normal immune response, resulting in
suppression of one or more immune
functions. These immune failures
predispose animals to severe vaccine
reactions, low humoral/local antibody
levels, and the presentation of diseases that
are typically controlled with normal
vaccination programs. In many occasions
these effects cannot be seen, so that only
lack of uniformity and poor productive
parameters are reported. Mycotoxins with
the strongest effect on birds' immune
system include aflatoxins, ochratoxins, and
the Trichothecenes group.
Figure 1. Bursal atrophy in 28-day-old broilers affected by mycotoxins. This indicates
damage to the immune system.
Figure 2. Normal bursae and spleens of 28-day-old commercial broilers. At this age,
bursal size should be 2- 2.5 times that of the spleen.
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