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Tend-R-Leen®
Tech Report
December
2009
Concerned
About Moldy Corn?
The
quality of the corn you feed your steers can have an impact
on their health and performance. Following are some
things to consider:
·
Moldy corn or
corn that is high in yeast can reduce cattle performance in
several ways. First, it can reduce intakes as the
cattle will not find it as palatable and it may have on off
taste. Secondly, mold can be toxic to cattle and can
cause mild to severe health problems.
·
Light test
weight corn can reduce gains.
·
Wetter corn has
different consequences depending on your storage system and
method of feeding. High moisture corn that is over 22%
and stored in a silo needs to be supplemented with roughage
and rolled. Dry corn that is over 16% may cause
moisture to get into the pellet, possibly causing the pellet
to crumble apart.
·
Corn with a
large amount of fines can cause bloating if the fines are
not removed. Corn that is very dry and handled
excessively can also produce more fines.
MOLD
& MYCOTOXINS
If
you have moldy corn, it is important to know which type of
mold you have and whether or not it can produce mycotoxins.
Following is an explantion of the most common types
of mold and mycotoxins.
Fungi
produce an array of chemical products known as secondary
metabolites. Penicillin is an example of a secondary
metabolite with medicinal applications. Unfortunately, not
all secondary metabolites are as useful as penicillin.
Mycotoxins are secondary metabolites of fungal origin that
are toxic to animals and humans. Disease that results from
ingestion of mycotoxin-contaminated feed or food by animals
or humans is called mycotoxicosis. Common examples of
mycotoxicosis are mushroom poisoning and ergotism.
Among
the thousands of species of fungi, only about 100 are known
to produce mycotoxins. Under favorable environmental
conditions, some toxigenic molds can produce mycotoxins on
agricultural commodities during plant growth, or after
harvest in storage and shipment. Some of the agricultural
commodities affected are cereal grains, soybeans, peanuts
and forage crops. Mycotoxin-contaminated feeds are of
critical importance due to their potential hazard to
livestock and poultry. Additionally, contaminated food
grains can affect human health.
In
the
Midwest
, the most common feed sources with mycotoxin contamination
problems are corn, wheat, forage and silage crops.
However, producers should be aware that mycotoxin
problems can be associated with grains and grain products
purchased off the farm or mixed in feed rations. Mycotoxin
problems are often aggravated by poor storage conditions.
General
symptoms of mycotoxicosis in domestic animals are: loss of
appetite, poor weight gain, feed refusal, diarrhea,
bleeding and unthriftiness.
Mycotoxicosis
is generally characterized by the following features:
·
The disease is not contagious
·
Antibiotics and drugs have little effect in controlling
the disease
·
Outbreaks are often seasonal
·
The problem is associated with a specific feed
·
Analytic assay of the feed indicates the presence of toxic
metabolites.
Following
is information about the major types of mycotoxins.
AFLATOXINS
Characteristics:
Aflatoxins
are secondary metabolites produced by some strains of
Aspergillus flavus and A. parasiticus, are the most commonly
occurring mycotoxins in feedstuffs worldwide. They are
a group of highly toxic metabolites that includes specific
forms designated as B1, B2, G1, G2, M1 and M2.
Aflatoxin B1 is the most commonly occurring type of
aflatoxin and a potent cancer-causing agent. It was
once thought that aflatoxin formation only occurred during
storage, but it is now well documented that aflatoxin
production also occurs in the field prior to harvest.
Aflatoxin contamination in corn is usually associated
with prolonged high day and night temperatures during the
growing season and severe drought conditions during grain
fill.
Crops
and weather conditions
Aflatoxins
can occur in corn and other cereal grains, peanuts,
cottonseed and other oil seed crops.
They are more common in grains from Southern regions
and are rare in Northern areas of the
U.S.
Field conditions conducive to A. flavus invasion of
grains and subsequent production of aflatoxin are:
·
Daytime high temperatures of 90°F or greater.
·
Relative humidity of 80% or above.
·
Ear injury caused by insects, birds or hail, as well as
drought stress, which predispose the crop to colonization by
the fungus and aflatoxin contamination.
·
Rainfall at the end of the growing season that postpones
harvest and prevents dry-down.
·
Storage conditions with corn moisture above 13% and
moderate temperatures increase the risk of aflatoxin
contamination.
Guidelines
for Grain Use
Because
of the carcinogenic properties of this mycotoxin, the
Federal Drug Administration (FDA) has established the
following guidelines:
The
maximum allowable level of aflatoxin in feed grains for
interstate commerce is 20 ppb.
The maximum level of aflatoxin in a complete feed
should not exceed 100 ppb for within state use.
Impact
on Animal Health—Aflatoxicosis
Caution
should be exercised when feeding contaminated rations to
livestock or poultry. There
is considerable variation in tolerance to aflatoxins among
the different animal species, for example:
·
Biological factors such as animal age and sex seem to play
a role in the ability of the animal to tolerate aflatoxins.
·
The main target organ is the liver. High doses cause liver
damage and hemorrhaging.
·
In general, young animals are more susceptible than
adults.
·
Aflatoxins are not considered a serious threat to
fertility, and are not likely to cause abortions at levels
that cause moderate disease.
·
Cattle are more tolerant than swine.
·
Dairy farmers should not feed aflatoxin-contaminated feeds
to lactating cows because the toxin will be transmitted into
the milk.
·
The major economic impacts of aflatoxicosis in dairy herds
are reduction in milk production and rejection of
contaminated milk.
·
Beef cattle exhibit a failure to gain weight or a
reduction in growth rate.
ZEARALENONE
Characteristics
Zearalenone,
also known as RAL and F-2 toxin, is a potent estrogenic
metabolite produced by some Fusarium species.
Several Fusarium species produce toxic substances of
considerable concern to livestock and poultry producers:
namely, deoxynivalenol, T-2 toxin, HT-2 toxin,
diacetoxyscirpenol (DAS) and zearalenone.
Crops
and Weather Conditions
Zearalenone
production does not seem to occur in significant amounts
prior to harvest, but under proper environmental conditions,
it is readily produced on corn and small grains in storage.
Alternating low and moderate temperatures in storage
promote production of this toxin. Temperatures between 53-57°
F induce the enzymes involved in biosynthesis of this toxic
substance, and optimum production occurs at 81° F.
The toxin is heat-stable, and it is not destroyed by
long storage, roasting, or by the addition of propionic acid
or mold retardants.
Impact
on Animal Health
·
Zearalenone is the primary toxin causing infertility,
abortion or other breeding problems, especially in swine.
·
When contaminated rations are consumed by animals, they
develop a condition known as hyperestrogenism.
·
Zearalenone has been associated with infertility and
abortion problems in dairy cattle in the Midwestern U.S.
·
Conception rates may be reduced in dairy heifers when fed
greater than 12.5 ppm zearalenone.
TRICHOTHECENES
Trichothecenes
are a large group of toxic metabolites that are produced by
many Fusarium species. Toxins of importance to livestock and
poultry producers are T-2 toxin and deoxynivalenol. Most
animals refuse to consume feeds with high concentrations of
trichothecenes, resulting in loss of weight.
Deoxynivalenol (DON)
Crops
and Weather Conditions
Deoxynivalenol
(DON), also known as vomitoxin, is produced by Fusarium
graminearum (Gibberella zeae) on corn and wheat prior to
harvest as well as during storage. Both Gibberella ear rot
of corn and Fusarium head scab of wheat are common diseases.
Impact
on Animal Health
DON
causes extensive feeding problems in swine.
Clinical
signs associated with consumption of a DON- contaminated
diet by hogs are vomiting and feed refusal, followed by loss
of body weight
Diets
containing 12 ppm, when consumed, provoked vomiting after 15
minutes.
Poultry
are also susceptible to DON.
Beef
cattle tolerate DON in feed at approximately 10 ppm in the
ration.
T-2
Toxin
One
of the most potent mycotoxins of the trichothecene group,
T-2 toxin, is produced in feedstuffs by several Fusarium
species.
Crops
and Weather Conditions
T-2
toxin is produced over a wide temperature range, with
maximum production occurring below 59° F. No T-2 toxin is
formed above 90° F. Corn
that is high in moisture content and stored in conventional
corncribs without artificial drying frequently becomes
“moldy” and is at risk of developing T-2 toxin problems.
Impact
on Animal Health
·
All farm animals are, to some extent, susceptible.
·
General symptoms in cattle are bleeding (uncontrollable,
at times, during castration or dehorning), inflammation of
the digestive tract, vomiting, diarrhea, decrease in milk
production, loss of appetite and feed refusal.
·
T-2 toxicosis epidemics also pose a threat to the poultry
industry. Clinical symptoms of T-2 toxicosis in poultry are
the appearance of lesions on the mouth and tongue that
impair eating.
·
Frequent defecation, vomiting, loss of weight and feed
refusal are some of the signs associated with T-2 toxicosis
in swine.
FUMONISINS
Characteristics:
Fumonisins
are toxins produced by Fusarium species that grow on several
agricultural commodities, mainly corn, in the field or
during storage. The disease, Fusarium kernel rot of corn, is
caused by Fusarium verticillioides and F. proliferatum,
common producers of fumonisin.
More than ten chemical forms of fumonisins have been
isolated, of which FB1 is the most prevalent in contaminated
corn and is believed to be the most toxic.
Crops
and Weather Conditions
Levels
of fumonisins in corn are influenced by environmental
factors such as temperature, humidity and rainfall during
pre-harvest and harvest periods.
High levels of fumonisins are associated with hot and
dry weather, followed by periods of high humidity. High
levels may also occur in corn that has been damaged by
insects and birds. Hybrids
genetically engineered to resist insects may have lower
levels of fumonisins. Improper
storage conditions, such as moisture above 18%, will
lead to increase fumonisin levels.
Impact
on Animal Health
·
Fumonisins are associated with a variety of adverse health
effects in livestock.
·
Fumonisins are known to cause a fatal disease in horses,
leucoencephalomalica.
·
Swine can develop fluid in the lungs (pulmonary edema)
and/or liver damage which causes reduced weight gain.
·
Cattle and sheep are comparatively resistant to fumonisins
with mild liver damage and moderate feed refusal.
·
Poultry are more resistant to fumonisins than other common
livestock.
PREVENTIVE PRACTICES
Prevention
is the best method to control mold growth and possible toxin
formation. The following practices can help minimize mold
growth and subsequent toxin production in storage.
Preharvest
·
Clean inside and outside of grain bins and dryers.
·
Prior to storage, check the condition of the bin for
possible water leaks, and clean it properly by removing
dust, dirt, leftover grain and other foreign material.
·
Crop rotation in many regions or tillage can reduce the
risk of Gibberella ear rot in corn and Fusarium head blight
of wheat. These practices have little effect on other corn
ear rots.
·
Some corn hybrids are more resistant to ear rots than
others, but overall, resistance to ear rots is not widely
available. Some Bt hybrids, those that produce BT in the
kernels, have less ear rot due to insect control resulting
in less toxin problems.
·
Control of second generation European corn borers and
other insect pests of corn ears can greatly reduce infection
by Fusarium and Aspergillus.
·
Few wheat varieties have high levels of resistance to
Fusarium head blight (scab). Plant moderately resistant
varieties when available. Planting several varieties that
differ in maturity will reduce the risk of disease to the
whole crop.
·
As with any crop pest, early detection through scouting
and early harvest can reduce serious losses and avoid
crises. Decisions on handling moldy grain should be made
before it is harvested. After harvest, spoilage can occur
quickly if delays result from indecision.
·
If extensive ear rot development is observed (10% or more
of the ears with more than 10-20% mold), the field should be
harvested as soon as moisture content reaches a level that
can be harvested. Even if some drying costs are incurred,
this will be less expensive than loss of crop value due to
mycotoxins and resulting feeding problems.
Postharvest
·
The crops should be allowed to mature in the field to the
following moisture contents: shelled corn, 23-25%; ear corn,
20-25%; small grain, 12-17%; and soybeans, 11-15%.
·
Harvesting equipment should be adjusted to minimize damage
to seeds or kernels and allow for maximum cleaning. Cracked
or broken seeds or kernels are more susceptible to mold
invasion.
·
Upon storage, dry the grain to 13-14%, if possible, within
48 hours. Long-term storage can be achieved at a uniform
moisture of 18% for ear corn; 13% for sorghum, wheat and
shelled corn; and 11% for soybeans.
·
After drying, store under cool temperatures (36-44° F).
·
Every few weeks check the condition of the grain for
temperature, wet spots and insects.
TESTING FOR MYCOTOXINS
The
presence of a fungus known to produce toxins is not proof
that the grain contains injurious levels of toxin.
It may be a good investment to collect a
representative sample and send it to a laboratory for
chemical analysis. The first step in mycotoxin
determination is sampling of the grain. Particular attention
should be given to the sampling procedure because sampling
error will be the greatest source of variation in the
analytical procedure. This variation is primarily due to the
uneven distribution of the mycotoxin contaminated kernels
within a lot of grain or feed.
The
ideal sampling procedure should assure the highest
probability of detecting mycotoxins even when contamination
is low. One
method of sampling grain is to use a probe sampler. Since
mold growth usually occurs in spots in the grain lot, best
sampling is done on recently blended lots of grain.
Another method is to collect small samples from the
moving stream of grain as it is moved in or out of the bins.
With both sampling methods, the collected grain is pooled
into a large aggregate sample that represents the lot.
For
shelled corn, it is recommended that the aggregate sample be
about 10 pounds. The aggregate sample should be coarsely
ground. Most analytical procedures need only about 25 grams
(0.9 ounces) of ground corn, so it is important that the
aggregate sample be thoroughly mixed after grinding. A one
or two pound sub-sample is then taken and it is more finely
ground. From this sub-sample a final sample is taken for
analysis.
A
number of commercial, university and government laboratories
perform mycotoxin analyses for a fee. Contact the lab to
determine the proper way to obtain and ship the sample.
Blending
is not an approved practice by the FDA for interstate
commerce. Blending is a practice intended to reduce toxins
to acceptable levels in small lots only for on farm use.
If the mycotoxin in the contaminated feed is known,
it may be a good idea to channel the feed to animals that
are more tolerant.
SUMMARY
The
best way to deal with mycotoxins is to try to prevent or
minimize their growth. Use best management procedures to
harvest, ensile, store and feed forages to prevent mold
growth. If
you have mold or mycotoxins in your feed, contact your
Tend-R-Leen Specialist for help in evaluating your feeding
options and developing a plan for the best method to feed
your cattle.
Portions of this article are from an article by:
Erick
DeWolf, Plant Pathologist,
Penn
State
University
Gretchen
Kuldau, Plant Pathologist,
Penn
State
University
Patrick
Lipps, Plant Pathologist, The
Ohio
State
University
Gary
Munkvold, Plant Pathologist,
Iowa
State
University
Paul
Vincelli, Plant Pathologist,
University
of
Kentucky
Charles
Woloshuk, Plant Pathologist,
Purdue
University
Dennis
Mills, Extension Associate, The
Ohio
State
University
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