Swine are sensitive to mycotoxins, especially nursing or nursery-age swine.
In general, mycotoxins cause reductions in feed intake, growth performance,
and immune function when levels are relatively low. Producers must be aware
that if one toxin is identified in a sample, the chances are high that other
toxins are present. Some toxins may not have been identified as of yet, but
research on known mycotoxins provides insight into the expected effects in swine
and potential methods to reduce those effects. Table 3 contains a summary of
the maximum permissible concentrations of mycotoxins in swine feeds.
has been the most extensively studied. Twenty to 200 ppb will cause a decrease
in feed intake and growth performance, which can be partially offset by increasing
specific dietary nutrients such as lysine or methionine. In severe cases (1,000
to 5,000 ppb) of aflatoxicosis, one can expect acute effects including death.
Aflatoxin M1 appears in milk of sows consuming aflatoxin-contaminated diets
and may affect piglets nursing those sows.
Feed concentrations of deoxynivalenol
(DON) of 300 to 500 ppb are often associated with feed refusal,
decreased weight gain, and increased incidence of infectious diseases. DON levels
greater than 1000 ppb, will cause feed refusal or decrease in feed intake resulting
in severe weight loss. It appears that pigs will often consume a sufficient
amount of contaminated feed to induce vomiting. In fact, DON is also called
vomitoxin because of its association with swine vomiting.
T-2 toxin has detrimental effects on swine performance, but no effect levels
have not been determined for commercial production environments. However, field
observations indicated that T-2 and related compounds are associated with decreased
productivity at feed concentrations of 200 ppb or less.
Zearalenone will significantly affect the reproductive performance of swine.
Prepuberal gilts are the most sensitive to zearalenone. The symptoms commonly
observed when feeding diets contaminated with zearalenone include a reddening
and increased size of the vulva, and increased size of mammary tissue. Zearalenone
will cause embryonic mortality at certain stages of gestation. Fertility problems
are often associated with zearalenone concentrations of 100 to 200 ppb in sow
Aflatoxin affects all poultry species. Although it generally takes relatively
high levels to cause mortality, low levels can be detrimental if continually
fed. Young poultry, especially ducks and turkeys, are very susceptible. As a
general rule, growing poultry should not receive more than 20 ppb aflatoxin
in the diet. However, feeding levels lower than 20 ppb may still reduce their
resistance to disease, decrease their ability to withstand stress and bruising,
and generally make them unthrifty.
Laying hens generally can tolerate higher levels than young birds, but levels
should still be less than 50 ppb. Aflatoxin contamination can reduce the birds'
ability to withstand stress by inhibiting the immune system. This malfunction
can reduce egg size and possibly lower egg production. In addition, one must
pay special attention to the use of contaminated corn in layer rations because
eggs are promptly used as human food and aflatoxin metabolites have been found
in egg yolks.
Mycotoxin levels found in most field situations tend to be low. Yet the combination
of low levels of mycotoxins with the stresses associated with commercial production
situations and/or exposure to disease organisms can produce effects in poultry
which are subtle, indirect, and sometimes ill-defined. Since the effects of
mycotoxins on poultry are dependant upon the age, physiological state, and nutritional
status of the animals at the time of exposure, and since mold growth at various
points within the feed production and distribution system can magnify mycotoxin
problems, mycotoxicoses can be difficult to diagnose in field situations.
Mycotoxins produced by the mold genus Fusarium include: T-2 toxin and it's chemical
relatives (trichothecenes), deoxynivalenol (DON), fumonisin, and zearalenone.
Other animals tend to be more sensitive to the effects of fumonisin, deoxynivalenol,
and zearalenone when compared to poultry. Nevertheless, detection of these mycotoxins
within poultry rations indicates that the ration or the ingredients within the
ration have been subjected to mold activity. Since numerous other mycotoxins,
as well as reduced nutritive value and palatability of feeds, are generated
by mold activity, the presence of fumonisin, deoxynivalenol, or zearalenone
in poultry feeds is cause for concern.
and trichothecenes can cause mouth and intestinal lesions as well as impair
the birds' immune response, causing egg production declines, decreased feed
consumption, weight loss, and altered feather patterns. While much is yet to
be learned, T-2 toxin and related compounds are currently thought to be the
most potent Fusarium mycotoxin for poultry.
DON alone has
few effects in poultry. However, in field situations the DON level is sometimes
associated with reduced feed consumption in layers and broiler breeders. This
means that DON may be an indicator that T-2 or other unknown Fusarium mycotoxins
Although the effects of mycotoxins on horses are not well documented in scientific
literature, in field situations apparent mycotoxin problems appear to be significant.
Mycotoxins have been implicated in a variety of health problems including colic,
neurological disorders, paralysis, hypersensitivity, and brain lesions. The
cumulative effect of feeding low levels of mycotoxins may also contribute to
a gradual deterioration of organ functions. This in turn affects growth rate,
feed efficiency, fertility, respiration rate, the ability to perform work, and
life span. Cases of mycotoxin-related horse deaths are consistently reported
throughout the southeastern United States. Due to the lack of conclusive scientific
research concerning the levels of various mycotoxins tolerated by the horse,
emphasis should be placed on feeding mycotoxin-free grain and forage to all
Horses are herbivores with a simple stomach (nonruminant). The large intestine
has an active microbial digestive ability to allow digestion of forages. However,
in the horse the small intestine, which is the major site of absorption, occurs
before the fermentative digestion. As a result, horses are more susceptible
to mycotoxins than ruminants, since nutrient absorption
occurs prior to fermentative digestion in the horse compared to ruminants in
which absorption occurs after fermentative digestion.
Productive or working horses have a high energy requirement and require a higher
concentrate intake, and thus would be most susceptible to problems with mycotoxin-contaminated
grains. Working horses would include growing horses less than two years of age,
brood mares in late gestation and early lactation, and horses at moderate or
intense work levels.
Other horses, that are only lightly worked, would be more likely to be exposed
to mycotoxin-contaminated hays or forages. Since moldy forages are generally
less palatable than normal forage, horses fed moldy forages typically refuse
feed before ingesting enough feed to cause severe intestinal tract damage. Mild
colic is typically noted in such cases. Unfortunately, most molds associated
with grains fed to horses do not readily affect palatability. Consequently,
horses are most often exposed to the mycotoxins found in grains. Grain mycotoxins
are readily absorbed and should be considered to be potentially lethal for horses.
Additional research is needed to clarify the effects of mycotoxins on horses.
Until such data exist, caution should be taken to select and feed mold-free
grains and forages.
Aflatoxin-contaminated feed not only reduces animal performance and overall
health, but it also creates risks of residues in milk. Aflatoxin is secreted
into milk in the form of aflatoxin M1 with residues approximately equal to 1
to 2 percent (1.7 percent average) of the dietary level. This ratio is not influenced
greatly by milk production level since higher producing cows consume more feed
and have a slightly higher transmission rate. Due to risks of milk residues,
dietary aflatoxin should be kept below 25 ppb. This level is conservative due
to: (1) non-uniform distribution of aflatoxin in grain and feed, (2) uncertainties
in sampling and analysis, and (3) the potential for having more than one source
of aflatoxin in the diet. Replacement animals may tolerate 50 to 100 ppb aflatoxin.
In dairy cattle DON is associated with reduced feed intake, lower milk production,
elevated milk somatic cell counts, and reduced reproductive efficiency. Milk
production loss appears to occur when diets contain more than 300 ppb DON. Although
controlled research has shown no cause and effect relationship between DON levels
and reduced milk production, field
observations have shown that reductions in milk output of 25 pounds per cow
were seen when DON was 500 ppb or more. This suggests that DON may serve as
a marker for feed that was exposed to a situation conducive to mold growth and
mycotoxin formation. The possible presence of other mycotoxins, or factors more
toxic than DON, seems likely. Dietary levels of 300 to 500 ppb DON in dairy
feeds indicate mycotoxin problems and warrant attention.
Zearalenone causes estrogenic responses in dairy cattle, and large doses of
this toxin are associated with abortions. Other responses of dairy animals to
zearalenone may include reduced feed intake, decreased milk production, vaginitis,
vaginal secretions, poor reproductive performance, and mammary gland enlargement
in virgin heifers. Establishment of a tolerable level of zearalenone for dairy
cattle is difficult, and is at best only a guess based on a meager amount of
data and field observations. As with DON, zearalenone may serve as a marker
for toxic feed. It is suggested that zearalenone not exceed 250 ppb in the total
In dairy cattle T-2 toxin has been associated with feed refusal, production
losses, gastroenteritis, intestinal hemorrhages, and death. T-2 has also been
associated with reduced immune response in calves. Data with dairy cattle are
not sufficient to establish a tolerable level of T-2 in the diet. Therefore,
a practical recommendation may be to avoid T-2 in excess of 100 ppb in the total
diet for growing or lactating dairy animals.
Fumonisin is another commonly isolated mycotoxin. However, fumonisin has only
recently been isolated and only enough data exist to know that levels in excess
of 20,000 ppb are potentially toxic to ruminants.
Aflatoxin and other mycotoxins can have considerable effects on beef cattle
although the problems are usually less critical than for swine and poultry.
Consumption of feeds highly contaminated with aflatoxin may reduce growth rate
and increase the amount of feed required per pound of gain. Calves are generally
more sensitive to feed contamination than adult cattle. In affected calves,
some cases have revealed severe rectal straining and a prolapsed rectum. Lactating
cows show a significant reduction in milk yield. Research has shown that high
levels of aflatoxin can also cause liver damage in adult cattle. Feeding a high
level of aflatoxin may also depress immune function, resulting in disease outbreaks.
Based on the feeds available, those contaminated with aflatoxin should be fed
at the lowest level possible and for the shortest period of time practical.
The effects of aflatoxin fed to cattle depend on the level of aflatoxin in the
ration, the length of the feeding period, and the age of the animal. If aflatoxin-contaminated
feeds must be fed to beef cattle, follow these guidelines (on a dry matter basis):
1. Creep feeds and diets
for gestating and lactating beef cows should contain less than 20 ppb of
2. Unstressed, growing-finishing
cattle in excess of 400 pounds may be fed diets containing up to 100 ppb
3. Diets for stressed feeder
cattle should contain no more than 20 ppb of aflatoxin. Stressful conditions
include weaning, shipping, extreme heat or cold, diseases, and parasites.
4. Animals destined for slaughter
should receive aflatoxin-free diets for at least 3 weeks before slaughter.
Since cattle in the southeast are typically fed high forage diets, they are
usually fed grain only as a supplement. Thus a relatively high level of aflatoxin
can occur in the grain before it exceeds the tolerable dietary level. In general,
cattle will eat about 2.5 percent of their body weight as dry matter. This can
be used to calculate the contribution of grain to their total ration, and the
tolerable level of aflatoxin in the grain. For example, growing calves weighing
600 pounds will consume about 15 pounds of total feed (600 lb multiplied by
2.5% equals 15 lb). If they are fed 3 pounds of grain plus forage-to-appetite,
the grain will make up about 20 percent of their total diet (3 lb divided by
15 lb equals 20%). In this case the grain may contain up to 500 ppb of aflatoxin
(100 ppb divided by 20% equals 500 ppb). Aflatoxin levels allowable in the grain,
given different rates of inclusion in the beef ration, are illustrated (Table
Other mycotoxins (DON, T-2, and zearalenone) present in grains, silages, and
hays may cause problems with performance and immune status of beef cattle. However,
little research is available on the levels of the individual toxins that may
be tolerated by animals. In cases of disease outbreaks and reproductive problems,
the feed should be tested for a full range of mycotoxins. Large producers should
consider routinely screening feeds for mycotoxins.
Prevention and Management
Prevention in Silages
Prevention of mycotoxins in silages includes following accepted ensiling practices
aimed at inhibiting deterioration primarily through elimination of oxygen. Some
silage additives (such as ammonia, propionic acid, microbial cultures, or enzymatic
silage) may be beneficial in preventing mycotoxins because they are effective
at reducing mold growth.
Silo size should be matched to herd size to ensure daily removal of silage at
a rate faster than deterioration. Feed bunks should be cleaned regularly. Care
should be taken to ensure that high moisture grains are stored at proper moisture
content and in a well-maintained structure.
Prevention of Feed Contamination
Controlling mold growth and mycotoxin production is very important to the feed
manufacturer and livestock producer. Control of mold growth in feeds can be
accomplished by keeping moisture low, keeping feed fresh, keeping equipment
clean, and using mold inhibitors. Grains and other dry feed such as hay should
be stored at a moisture level 14 percent or less to discourage mold growth.
Aeration of grain bins is important to reduce moisture migration and to keep
the feedstuffs dry.
Moisture is the single most important factor in determining if and how rapidly
molds will grow in feeds. Moisture in feeds comes from three sources: (1) feed
ingredients, (2) feed manufacturing processes, and (3) the environment in which
the feed is held or stored. To control the moisture content of feeds successfully,
moisture from all three sources must be controlled.
Moisture in Feed Ingredients
Since corn and other grains are a primary source of the moisture and molds
found in feed, the first important step in controlling moisture in feed is to
control it in the grains from which the feed is prepared. Since all feed ingredients
contain moisture, they should be monitored and their moisture content controlled.
It is commonly believed that the amount of moisture in grain is too small to
permit mold growth except in rare and unusual circumstances. However, moisture
is not evenly distributed in grain kernels. A batch of grain containing an average
of 15.5 percent moisture may, for example, contain some kernels with 10 percent
moisture and others with 20 percent moisture. The moisture content of individual
grain kernels is directly related to the amount of mold growth that occurs:
that is, kernels with higher moisture contents were more susceptible to mold
growth. In addition to moisture, the amount of mold growth is about five times
greater for broken kernels than for intact kernels. Thus the fraction of commercial
grain, known as broken kernels and foreign matter, can be expected to have a
higher mold and mycotoxin content than the portion composed of whole kernels.
Moisture in Feed Manufacturing
Grains are commonly ground with a hammer mill to aid in mixing and handling,
to improve digestibility, and to improve the pelleting process. This grinding
process creates friction, which causes heat to build up. If unchecked, temperature
increases greater than 10 degrees Fahrenheit will cause significant migration
of grain moisture encouraging mold growth. This is particularly true in cold
weather when temperature differences cause moisture to condense on the inside
walls of bins. Air-assisted hammer-mill systems reduce heat buildup in the product
and, in turn, reduce moisture problems.
The pelleting process involves mixing steam with the feed, pressing the mixture
through a die, and then cooling the pellets to remove heat and moisture. Generally,
heat and 3 to 5 percent moisture are added to the feed during the pelleting
process in the form of steam. If the pelleting process is done correctly, this
excess moisture is removed from the feed before shipment. If, however, this
excess moisture is not removed when the pellets are cooled, mold growth will
Since feeds containing moisture are warmer than normal, storing hot or warm
pellets in a cool bin will cause moisture to condense on the inside of the bin.
Although pelleting of feed has been shown to reduce mold counts by a factor
of 100 to 10,000, many mold spores remain in the feed after it has been pelleted.
After pelleting, the remaining spores can grow if conditions are right. Thus
the pelleting process delays, but does not prevent, the onset of mold growth
and plays only a minor role in efforts to control molds. In addition, pelleted
feeds may be more easily attacked by molds than nonpelleted feeds.
Moisture and Feed Storage Environment
To control mold growth, obvious sources of moisture in the feed handling and
storage equipment must be eliminated. These sources may include leaks in feed
storage tanks, augers, roofs (either at the barn or at the feed mill), and compartments
in feed trucks.
A fact about feed moisture often overlooked is that it changes in relation
to the feed's environment. Since animals kept in confinement housing add moisture
to their environment by respiration and defecation, the air in these houses
can be very humid. Feed that was initially very low in moisture content will
gain moisture when placed in a humid environment. The humidity in confinement
housing should therefore be controlled by providing adequate ventilation.
Keeping Feed Fresh
Time is required for both mold growth and mycotoxin production to occur. It
is therefore important to have feeds delivered often so that they will be fresh
when used. Feeds should generally be consumed within 10 days of delivery.
It is equally important to manage the feed delivery system to ensure that feeds
are uniform in freshness. Field surveys have shown that poultry farms producing
birds with the poorest performance were those with the most feed in their feeder
On these farms, the feeds contained the greatest amount of moisture and had
the highest number of molds. If the feeder system is allowed to keep the feed
pans full at all times, the feed in the pans will be significantly older than
that in the storage tank.
The animals will tend to eat primarily the feed in the top layer, and the feed
at the bottom of the pans will age, providing greater opportunities for molds
to grow. The animals' performance may suffer as a result. To prevent this problem,
the feeder system should be turned off weekly. The animals will then be forced
to clean out all of the feed in the feeders before it becomes excessively old.
A similar principle applies to feed storage tanks. The feed next to the wall
is last to exit the tank and therefore stays in the tank the longest. The feed
in contact with the wall is also the only portion of the feed that changes appreciably
due to temperature. These factors make feed in contact with the wall susceptible
to moisture migration and mold growth. It is best to maintain two feed tanks
so that one tank can be completely emptied and cleaned before it is refilled
with new feed.
When feed is manufactured and delivered to farms, it may come in contact with
old feed that has lodged or caked in various areas of the feed storage and delivery
systems. This old feed is often very moldy and may "seed" the fresher
feed it contacts, increasing the chances of mold growth and mycotoxin formation.
To prevent this problem, caked, moldy feed should be removed from all feed manufacturing
and handling equipment.
Use of Mold Inhibitors
The use of chemical mold inhibitors is a well-established practice in the feed
industry. However, mold inhibitors are only one of several tools useful in the
complex process of controlling the growth of molds, and they should not be relied
The main types of mold inhibitors are (1) individual or combinations of organic
acids (for example, propionic, sorbic, benzoic, and acetic acids), (2) salts
of organic acids (for example, calcium propionate and potassium sorbate), and
(3) copper sulfate. Solid or liquid forms work equally well the inhibitor is
evenly dispersed through the feed. Generally, the acid form of a mold inhibitor
is more active than its corresponding salt.
Many factors influence the effectiveness of mold inhibitors, and proper attention
to these factors can enhance the benefits they provide. Mold inhibitors cannot
be effective unless they are completely and thoroughly distributed throughout
the feed. Ideally, this means that the entire surface of each feed particle
should come in contact with the inhibitor and that the inhibitor should also
penetrate feed particles so that interior molds will be inhibited.
The particle size of the carriers for mold-inhibiting chemicals should be small
so that as many particles of feed as possible are contacted. In general, the
smaller the inhibitor particles the greater the effectiveness. Some propionic
acid inhibitors rely on the liberation of the chemical in the form of a gas
or vapor from fairly large particle carriers. Presumably, the inhibitor then
penetrates the air spaces between particles of feed to achieve even dispersion.
Effect of Feed Ingredients
Certain feed ingredients may also affect mold inhibitor performance. Protein
or mineral supplements (for example, soybean meal, fish meal, poultry by-product
meal, and limestone) tend to reduce the effectiveness of propionic acid. These
materials can neutralize free acids and convert them to their corresponding
salts, which are less active as inhibitors. Dietary fat tends to enhance the
activity of organic acids, probably by increasing their penetration into feed
particles. Certain unknown factors in corn also alter the effectiveness of organic
When mold inhibitors are used at the concentrations typically recommended,
they in essence produce a period of freedom from mold activity.
If a longer mold-free period is desired, a higher concentration of inhibitor
should be used. The concentration of the inhibitor begins to decrease almost
immediately after it is applied as a result of chemical binding, mold activity,
When the concentration of the inhibitor is reduced until it is incapable of
inhibiting mold growth, the mold begins to use the inhibitor as a food source
and grows. In addition, feeds that are heavily contaminated with molds will
require additional amounts of inhibitor to achieve the desired level of protection.
Influence of Pelleting
The widespread use of pelleted feeds in the feed industry is beneficial to
the use of mold inhibitors. The heat that the feed undergoes during pelleting
enhances the effectiveness of organic acids. Generally, the higher the pelleting
temperature, the more effective the inhibitor. Once mold activity commences
in pellets, however, it proceeds at a faster rate than in nonpelleted feed because
the pelleting process that makes feed more readily digestible by animals also
makes it more easily digested by molds.
The practice of recommending copper sulfate as a treatment for fungal diseases
in animals goes back many decades. The effectiveness of copper as a mold inhibitor
is difficult to document. Although copper sulfate in the diet has been shown
to improve body weight and feed conversion efficiency in broilers, excessive
levels of copper may be toxic to young animals and will accumulate in the environment.
In addition, recent research has indicated that feeding copper sulfate to poultry
causes the formation of mouth lesions similar to those formed by some mycotoxins.
Similar mouth lesions might be formed in other animal species.
If unacceptable mycotoxin levels occur, removal of the contaminated feed is
preferable. While it is often not possible to completely replace the ration,
particularly the forage ingredients, obviously, moldy feeds should be removed.
Acidic diets may intensify the effects of mycotoxins and should be avoided in
these situations. Increasing nutrients such as protein, energy (fats and carbohydrates),
and vitamins in the diet may also be advisable. The addition of antioxidants
to the animal assists in dealing with the effects of mycotoxins.
The use of inorganic binders/clays
Mineral clays to Chemi-bind mycotoxins, and prevent them from being absorbed
by the animal's GIT, has received a lot of research attention recently. These
clay products (which include zeolites, bentonites, bleaching clays and hydrated
sodium calcium aluminosilicates [HSCAS]) have been shown to change the responses
of rats to Zearalenone and T-2 toxin. However, it should be clearly understood
that binding of some mycotoxins may be weak or nonexistent and that clay products
differ in their ability to bind mycotoxins. While HSCAS products has been shown
to bind aflatoxin protecting animals against aflatoxicosis, they have not shown
to possess binding affinity to Fusarium Toxins.
Mycotoxin Sampling, Testing, and Test
Since mycotoxins are not evenly distributed in grain or in mixed feeds, taking
a feed or grain sample which will give a meaningful result in mycotoxin analyses
is difficult. Grab samples generally give very low estimates of mycotoxin content.
In fact, nearly 90 percent of the error associated with mycotoxin assays can
be attributed to how the original sample was collected. This is due to only
1 to 3 percent of the kernels in a contaminated lot containing mycotoxin, and
these contaminated kernels are usually not evenly distributed within the lot
For whole kernel grains, a properly taken composite sample of at least ten
pounds is required for a reasonably accurate, mycotoxin analysis. Trucks can
usually be sampled with a grain probe, but bins must often be sampled as grain
is being withdrawn.
Analytical techniques for the detection of mycotoxins continue to improve.
Several commercial laboratories now test for a variety of mycotoxins.
Although analytical costs can be a constraint, these costs may be insignificant
compared with the economic consequences of production and health losses associated
with mycotoxin contamination.
Commercial antibody test kits for screening or quantitation are currently available
for aflatoxins, zearalenone, deoxynivalenol (DON), T-2 toxin, ochratoxin A,
and fumonisins. These antibody methods, while they are still being improved,
are good if used properly.
Suggested Further Reading
Anonymous. 1979. Aflatoxin and other mycotoxins: An agricultural perspective.
Council for Agricultural Science and Technology, 250 Memorial Union, Ames, IA
50011, Report No. 80, pp 56.
Anonymous. 1989. Mycotoxins economic and health risks. Council for Agricultural
Science and Technology, 250 Memorial Union, Ames, IA 50011, Report No. 116,
Bray, G. A. and D. H. Ryan, eds. 1991. Mycotoxins, cancer, and health. Pennington
Center Nutrition Series, Vol. 1, Louisiana State University Press, Baton Rouge,
LA, pp 331.
Coelho, M. B. 1990. Molds, mycotoxins and feed preservatives in the feed industry.
BASF Corporation, 100 Cherry Hill Road, Parsippany, NJ 07054, pp 159.
Robens, J. F. ed. 1990. A perspective on aflatoxins in field crops and animal
food products in the United States: A symposium. U.S. Department of Agriculture,
Agricultural Research Service publication number ARS-83, pp 157.
Shimoda, W. 1979. Conference on mycotoxins in animal feeds and grains related
to animal health. U.S. Department of Commerce. National Technical