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Mycotoxins in dairy cows can be a big issue. A healthy
rumen can protect cattle against low levels of mycotoxins,
but not all. Often, these hidden thieves are likely to be
responsible for numerous undiagnosed health issues. In
extreme cases, they can cause abortions, severe scouring
and sudden milk drop. But for the majority, any mycotoxin
presence is more likely to be seen as a subtle problem.
Perhaps the cows are not milking as well as they should be,
or the dung is a little loose and variable or cell counts have
crept up and fertility is falling away.
The complex diet challenge
The diet of a dairy cow typically contains both concentrates
and forages. This increases the risk of exposure to multiple
mycotoxins. Forages (grazed and conserved), fermented
feeds and by-products all represent a signifi cant risk to
cattle, depending on soil contamination, forage harvesting
date, silage management, purchased feed origins and on-
farm feed storage conditions.
It is important to note that mycotoxins seldom occur in
isolation. It is not uncommon to fi nd multiple mycotoxins
in the diet of dairy cows. This allows for interactions
between them, which leads to synergistic or additive
e ects.
Mycotoxin sources
Forages: Mycotoxins in forages (e.g., grass, hays,
silages, straw) present the greatest threat to cattle.
Even fresh grass for grazing can be contaminated
with several mycotoxins. These typically include
fungal endophytes that produce mycotoxins that
protect the plant in some way, such as ergovaline
and lolitrem B, as well as Fusarium mycotoxins, such
as zearalenone or deoxynivalenol (DON).
Identifying moulds in silage (Mahanna, 2009):
Mould colour
Associated toxin(s)
Ochratoxin, citrinin, patulin

Zeralenone, DON, T-2, Fumonisin
Alltech 37+ mycotoxin analysis has shown that
mycotoxins can be found throughout Ireland. To date, 248
Irish forage samples have been tested in the Alltech 37+
mycotoxin analytical services laboratory. Of the samples
tested, 94 per cent contained mycotoxins, with an average
of 4.62 mycotoxins present in each sample.
The majority of these are from the fungi family and are
producing Penicillium and Fusarium moulds. These will
hamper natural bacterial activity in the rumen.
The spread and multiplication of these throughout the
pit is infl uenced by silage dry matter and the quality of
preservation. Drier forages with a poor level of preservation
will rapidly develop moulds. It is important to bear in
mind that straw bedding can also be contaminated with
mycotoxins. This can present a risk to dry cows that often
consume large quantities of straw and forage.
Risk to dairy cows
Mycotoxins are often responsible for numerous
undiagnosed health issues in dairy cows, even when
growing, harvesting and pit management is reasonably
good. It is important to note that many of the symptoms
associated with mycotoxicosis are non-specifi c, often
meaning that a mycotoxin issue is `last in the queue'
when diagnosing. The main e ect of many mycotoxins is
impairment of the immune system. Immune-compromised
animals will be at greater risk of pathology from other
infectious and metabolic diseases, simply as a result of their
`weakened' state. Other e ects include gastrointestinal
Are mycotoxins really
dangerous for dairy cows?
Richard Dudgeon, Regional manager, Alltech Northern Ireland,
examines the issue of mycotoxins
Mycotoxin Occurrence %
Aslatoxins B
Aslatoxins, Total
Type B Trichothecenes
Type A Trichothecenes
Fusaric Acid
Emerging Mycotoxins
Other Penicillium Mycotoxins
Other Aspergillus Mycotoxins
Ergot Toxins