Home' NZ Dairy Farmer : December 2013 Contents 4 The Dairyman December 2013
UNIVERSITY of Guelph Professor
Trevor Smith has spent the last 36
years studying ''mouldy feed''.
It doesn't sound like a particularly
important or interesting topic to have
studied for this length of time but the
reality is very different; it is not only an
issue that has an enormous impact on
animal health and welfare, but many more
years of research are needed to under-
stand its full implications.
It is not mouldy feed itself that is the
problem, but rather what is growing
inside the feed; mycotoxins, or the toxic
substances naturally produced by moulds
or fungi, can cause a huge variety of
health problems for animals, some fatal,
and are far more complex than first
thought when research began in the
Prof Smith was the keynote speaker
at the Alltech Mycotoxin Management
Summit held in Auckland last month, and
he provided attendees with a summary
of his research into the toxins found in
He said silages are likely a major source
of mycotoxins in dairy feeds, which are
created when fungi migrate up the stalks
of plants, using the nutrients provided
by the host plant and thus reducing the
nutritional value of the plant.
Prof Smith said aflatoxin and fusarium
toxins are the most commonly found
mycotoxins in dairy cow feed, while
Mouldy feed a silent killer
silages can contain additional aspergillus
and penicillium toxins.
''We know very little about the individ-
ual toxicity of most of these compounds
as they are never found alone,'' he said.
Ruminant animals such as dairy cows
are most resistant to fusarium myco-
toxins, due to the influence of enzymes
which partially stop mycotoxins before
they enter the bloodstream, but their
health is still compromised.
''Mycotoxins have profound nega-
tive effects on performance and health
in dairy cows, with different problems
arising depending on the mycotoxin, or
combinations of mycotoxins present in
feed,'' Prof Smith said.
He gave examples of several mycotox-
ins and the animal health problems result-
ing from feed contamination.
Deoxynivalenol, the most common
toxin in the trichothecenes family, alters
brain chemistry, inhibits cellular protein
synthesis in the epithelial lining of the
digestive tract (causing haemorrhaging)
and has an immunosuppressive effect,
causing animals to become more suscepti-
ble to secondary mycotoxic disease.
Zearalenone causes prolapse, abortions
and infertility, and fusaric acid is a phar-
macologically-active compound which
converts dopamine to norephinephrine,
causing a drop in blood pressure (result-
ing in oedema and swelling in udders
and feet) and an increase in serotonin
and tryptophan in the brain (resulting in
reduced feed consumption, loss of muscle
co-ordination and lethargy).
Prof Smith also quoted a study of 18
mid-lactation holstein friesian cows which
were fed a variety of diets including hay,
silage, corn or wheat over 56 days, some
containing fusarium mycotoxins.
While somatic cell count showed
an insignificant change, the fusarium
toxin's effects on immunity were more
significant; blood urea rose significantly,
demonstrating impaired immuno-acid
''Feedstuff contaminated with myco-
toxins can alter metabolism and lower
productivity of livestock and poultry,
leading to significant financial and
production losses,'' Prof Smith concluded.
However, he said losses could often be
prevented by the use of an appropriate
mycotoxin adsorbent, or binding agent.
It is believed that the agents in these
feed additives bind to the mycotoxin,
preventing them from being absorbed,
and both are then excreted in the manure.
Inorganic mycotoxin binders are silica-
based polymers, while organic mycotoxin
binders are carbon-based polymers.
Mycotoxin adsorbents offer a short-
term solution to the challenge of myco-
toxin-contaminated animal feeds. Myco-
toxins are stable chemical compounds, as
opposed to living organisms like moulds
and yeasts, and so are difficult to destroy.
The only complete solution to the
mycotoxin challenge will be the long-term
goal of eliminating mycotoxins from the
food and feed chains through improved
quality control based on better analytical
techniques coupled with genetic advances
in plant resistance to fungal infestation.
Checking feed: Professor Trevor Smith, Dr Jorge Pena, Dr Lucy Waldron and Nigel Meads spoke at the Alltech NZ Mycotoxin Management Summit.
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