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Feeding & Animal Nutrition

Feeding and Animal Nutrition

Cow Eating


Iowa State University Veterinary Diagnostic and Production Animal Medicine

Mycotoxin Concerns in Sheep and Meat Goat Feeding
Purdue Extension publication AS-597-W

Zearalenone Concerns in Reproducing Livestock
Purdue Extension publication AS-598-W

Don't rely on chemicals to reduce vomitoxin contamination of corn
AgAnswers article from 2010


Frequently Asked Questions

What's the relationship between molds and mycotoxins in feed?
All homegrown feeds contain some mold spores. When temperature and moisture are right, these spores can germinate and the mold will grow. Many molds found in feeds are not toxic, but some species produce mycotoxins that can reduce animal health and productivity.


At what level do mycotoxins become a problem in beef cattle rations?
While there are recommended cautionary levels, there is not a black and white answer to this question. There is a limited amount of research data to help identify maximum safe mycotoxin levels in animal diets. Much of the research conducted has evaluated the effects of adding a pure mycotoxin into a "clean diet." However, a mycotoxin provided by a naturally contaminated feed appears to be more toxic than the same level of a pure mycotoxin supplemented into a clean diet, presumably due to the presence of multiple mycotoxins in naturally contaminated feeds.

In addition, little is known about the effects of interactions when one or more mycotoxins are present. Furthermore, other factors, including animal species, gender, age, stage of production, duration of exposure, stress levels, and immune status, make it difficult to determine safe levels of individual mycotoxins.


While it is extremely difficult to make blanket recommendations for all classes of cattle, feedlot cattle are less susceptible than younger cattle, higher-stress cattle, breeding males and females, or pregnant females. Young calves and virgin replacement heifers are more sensitive to mycotoxins followed in descending order by:
  1. Cows in early lactation prior to breeding
  2. Nonlactating mature cows
  3. Feeder/feedlot cattle
Aflatoxins cause liver damage, decreased milk and egg production, and suppression of immunity in animals consuming low dietary concentrations. Aflatoxin can appear in milk, which can pose a risk to nursing livestock and humans.

The U.S. Food and Drug Administration has established levels for aflatoxin danger, and can take enforcement action if it is sold and found to contain amounts above the "action level" for it's final end use.


FDA Maximum Feeding Levels (parts per billion)

End Use of Grain

20 ppb

Animal feed and feed ingredients intended for dairy, immature poultry, and stressed animals

20 ppb

Human consumption

100 ppb

Grain intended for breeding cattle, breeding swine, and mature poultry (such as laying hens or breeding birds)

200 ppb

Grain intended for finishing swine of 100 pounds or greater

300 ppb

Grain intended for finishing beef cattle


Cattle are quite tolerant of deoxynivalenol, often referred to as DON, because the rumen microflora have the ability to degrade at least part of the mycotoxin present in the diet. There have been reports of no adverse effects when cattle have consumed up to 10 ppm DON. In addition, no adverse effects on health or production performance were reported in several studies with growing/finishing cattle when dietary dry matter concentrations were 18-21 ppm DON.

Advisory levels from FDA, however, indicate that DON levels should not exceed a total dietary dry matter concentration of 5 ppm in ruminating beef cattle older than 4 months of age. Whenever possible, avoid feeding DON-contaminated feed to virgin heifers, young calves, cows in early lactation, and pre-breeding cows. Growing/finishing cattle are the most logical candidates for feeding corn that contains significant concentrations (> 5ppm) of DON.

Zearalenone (also known as ZEA) is a mycotoxin that has estrogen-like activity, which can have a detrimental effect on reproduction. The negative effect of ZEA can be exacerbated by phytoestrogens from other feed sources and this additive effect needs to be considered when formulating diets. Reports indicate that cattle consuming more than 10 ppm zearalenone may experience infertility and estrous cycle disruptions. Reproductive performance of virgin heifers, however, appears to be affected when dietary ZEA concentrations exceed 5 ppm. At present, no FDA action, advisory or guidance levels have been established for zearalenone in U.S. feed supplies.


Guidelines for maximum mycotoxin levels in complete beef cattle diets


Ruminating beef animals more than 400 lbs

5 ppm


Virgin heifers

5 ppm


Early lactation cows, pre-breeding

10 ppm


Non-lactating mature cows, growing/finishing cattle

20 ppm


Once the level of mycotoxin contamination is determined, a plan of action can be made. If mycotoxins are present, the safest approach would be to discard the feed supply, but this is obviously not feasible in most scenarios. Dilution with clean feeds is the next best method to lower total levels of mycotoxins in livestock diets. Finally, whenever possible, feed rations contaminated with mycotoxin to growing and finishing cattle, which will be the least affected by mycotoxin exposure.


If I didn't test my grain, what do I look for that might indicate I am having performance issues? In other words, what are the symptoms of mycotoxicity?
Obviously, the visible presence of mold in corn or other feeds is a clear indication the feed must be tested, but mycotoxins may be present even if the feeds do not appear abnormal. In many cases, monitoring animal performance can uncover mycotoxin problems. The most obvious indicator that you have moldy feed is that animals consume less feed because it has lower palatability. This reduction in feed intake can occur, however, with or without the presence of mycotoxins. In addition, a reduction in diet digestibility of 5-10% has been reported when higher levels of mold are present in the diet. A reduction in feed intake and diet digestibility will result in lower growth rates, poor feed conversion, general unthriftiness, weight loss, and lower milk production.

When DON levels reach 1ppm, swine begin to refuse feed and can exhibit vomiting. Ingestion of ZEA-contaminated corn can result in the development of feminine characteristics in males, premature sexual development of young females, infertility in adults, abortion, stillbirth, and the birth of deformed offspring. Cattle may have swollen vulvas and nipples and vaginal and rectal prolapse may occur. A reduction in feed intake and perhaps feed refusal has been observed. This effect is most clearly seen in pigs, but clinical signs can also be observed in cattle.


Mycotoxins, in large doses, can lead to acute health or production problems in a dairy herd. Unfortunately, health issues can result from many causes, and often a run of abortions and severely impaired fertility are the first mycotoxicity symptoms observed. However, it is more likely that mycotoxins will be a factor contributing to chronic problems, including a higher incidence of disease, poor reproductive performance, or suboptimal milk production. Ruminal degradation of mycotoxins helps to protect cows against acute toxicity, but may contribute to chronic problems associated with long-term consumption of low levels of mycotoxins.

In general, mycotoxins exert their effects through several means:
  1. Reduced intake or feed refusal
  2. Reduced nutrient absorption and impaired metabolism
  3. Altered endocrine and exocrine systems
  4. Suppressed immune function
  5. Altered microbial growth
Remember, the only way to know whether mycotoxins are present and the extent of their presence is to have feed tested, including grains and corn silage.


How do I sample forages and total rations for mycotoxins?
The American Feed Industry Association (AFIA) indicates that obtaining representative samples from bulk shipments including barges, rail cars, and trailers is difficult because of hot spots and stratification within loads. However, collecting a representative sample is critical for obtaining an accurate estimate of mycotoxin concentration. Studies have shown that up to 90 percent of the variability in test results comes from sampling variability.


For stationary shelled corn, samples can be collected using a grain probe. Collect four to 10 probes that contain 1 pound each(preferably 10). For a moving stream of grain, carefully take grab samples while taking care to avoid personal injury. Mix the samples well and take a 1- or 2-pound subsample from the original 10-pound sample. Once collected, handle samples properly to prevent further mold growth. Wet samples may be frozen or dried before shipment, and transit time should be minimized. If multiple samples are to be submitted for testing, thoroughly clean grinding and sampling equipment between samples. Mold spores can cause respiratory problems, so wear a dust mask when grinding, mixing, and dispensing moldy feed samples.


Take forage samples using grab samples or cores. Because the presence of the mold may vary greatly over fields (and, therefore, within the stored silage), it is critical to sample across the entire volume of forage in storage. Layering of silage in upright silos and bags will likely require a series of samples to be submitted over time to check for the presence of mycotoxins in feed currently in use. Most forage labs are equipped to test forages for the presence of mycotoxins, but you must specifically request that they test for mycotoxins.


What is the relationship between deoxynivalenol (DON) and zearalenone (ZEA)?
The relationship between DON and ZEA is not clearly understood in a natural feed such as corn. Most of the research conducted has evaluated the effects of adding a pure mycotoxin into a "clean diet." However, a mycotoxin provided by a naturally contaminated feed appears to be more toxic than the same level of a pure mycotoxin supplemented into a clean diet, presumably due to the presence of multiple mycotoxins in naturally contaminated feeds.


Little is known about the interaction of DON and ZEA when they are present together. Interactions of mycotoxins with each other and with other factors, including animal species, gender, age, stage of production, duration of exposure, stress levels, and immune status, make it difficult to determine safe levels of mycotoxins when only one mycotoxin assay has been conducted. Therefore, the impact on animal response to a combination of DON and ZEA in feeds could be quite different than the isolated response to each of these mycotoxins. In addition, the ratio of these two mycotoxins to one another likely has an impact on animal response to the mold in corn.


Are there other factors that need to be considered when evaluating a mycotoxin assay?
Conjugated mycotoxins in which a mycotoxin is bound to another substance, such as a sugar, may be "masked" during laboratory analysis and still be toxic to animals. Both zearalenone (Gareis et al., 1990) and deoxynivalenol (Berthiller et al., 2005) can occur in "masked" forms. Therefore, mycotoxicoses cases may have occurred in situations where "masked" mycotoxins yielded lab test results indicating the presence of low mycotoxin concentrations, even though actual mycotoxin levels in the feed were much higher.


What kinds of feeds can I expect to find toxins?
Mycotoxins can be found in different concentrations in different parts of the plant. For example, concentrations of deoxynivalenol (DON) and zearalenone (ZEA) may be 5-10 times greater in the cob and husk than in the grain. Risk factors for high mycotoxin concentrations in the crop residue include moldy ears, stalk rot, insect damage, and lodging.


Unfortunately, accurate sampling of crop residue can be challenging. As such, the decision about whether to graze a field should be based on the mycotoxin analysis of the grain, along with assessment of the other risk factors mentioned. A general rule of thumb is that if the grain contains 1ppm of a mycotoxin, it is likely safe to graze. However, if the grain contains concentrations above these levels, it is recommended to harvest the crop residue in bales, core sample, analyze samples for mycotoxin concentrations, and feed accordingly.


Molds are destroyed during ethanol fermentation, but mycotoxins remain. Therefore, distiller's grains (DGs) and corn gluten feeds can contain high levels of mycotoxins since they are concentrated approximately three fold compared to the original grain. Most ethanol plants are testing for mycotoxins and segregating batches of corn and DGs by level of mycotoxin. Buyers should be able to obtain the mycotoxin levels.


Corn grain and corn silage can both contain mycotoxins when fed after storage. The risk of DON is greater when grain moisture is 21% or more, and temperatures are in the range of 70-84°F. The growth of molds that produce mycotoxins in corn grain will be slowed, or even stopped when corn is dried down, but the mold is not destroyed. Under the right moisture and temperature conditions, mold growth can flare up in stored corn.


When corn grain is ensiled, the Fusarium molds will die off, but any mycotoxins present will not be destroyed. Other fungi such as Aspergillus and Penicillium species can survive the ensilage process. Molds and mycotoxins in corn silage would respond similarly to ensiled corn. Corn screenings are often an economical feed resource, but screenings can contain particularly high levels of mycotoxins. Moldy kernels tend to be brittle and are easily cracked. Therefore, loads of corn that result from coring bins can contain high levels of mycotoxins. Conversely, removing fines, damaged seeds, and cracked corn kernels can reduce toxin risk.


What are the reproductive problems that may arise from using feedstuffs contaminated with mycotoxins?
Mycotoxins in corn and other grains can have detrimental effects on reproducing males and females. For the reproducing animals, zearalenone (ZEA) is of the greatest concern. Zearalenone competes with the naturally produced reproductive hormone estradiol-17ß for binding sites (estradiol receptors) in various organs in the bodies of both males and females and thus can interfere with normal reproductive functions.


Swine are the most sensitive livestock to ZEA concentrations in their feed. The amount of ZEA that can negatively affect the reproductive performance of swine depends on the age of the animal, stage of the estrous cycle or pregnancy, as well as level and duration of exposure. As little as 1-5 ppm of ZEA in the diet of pre-pubertal gilts can induce clinical signs such as swelling of the vulva, vaginal and rectal prolapses, and alterations within the uterus.


Additionally, ZEA can induce infertility by altering normal ovarian function, follicular development, and normal uterine function. Therefore the diet for pre-pubertal gilts and young boars should not contain over 1 ppm ZEA. In sows and pubertal gilts, ZEA concentrations in the diet of 3-10 ppm can cause abnormal estrous cycles. Sows may frequently display heat, show heat and fail to ovulate, or fail to show heat due to pseudo-pregnancy. For breeding sows and gilts, the final diet should not exceed 2 ppm ZEA. Exposing pregnant sows or gilts to ZEA concentrations greater than 60 ppm can cause embryonic mortality and causes genitalia defects of the offspring exposed to ZEA while in utero. Therefore, gestating females should not receive a diet with greater than 25 ppm ZEA.


Although cattle are not as sensitive to ZEA-contaminated feed as swine, exposure of breeding stock to ZEA still has the potential to negatively impact reproductive performance. For cattle, virgin heifers are of greatest concern and the diet should not contain over 5 ppm of ZEA in the total ration. Non-lactating pregnant cows can be fed diets containing up to 20 ppm ZEA, but lactating cows, especially during and immediately after the breeding season, should not receive diets containing more than 10 ppm ZEA.


For More Information

Todd Applegate, Extension Animal Scientist, Poultry
(765) 496-7769, Email:

Ron Lemenager, Extension Animal Scientist, Beef
(765) 494-4817, Email:

Tamilee Nennich, Dairy Cattle Nutritionist
(765) 494-4823, Email:

Brian Richert, Extension Animal Scientist, Swine Nutrition and Management
(765) 494-4837, Email:

Mike Schutz, Extension Animal Scientist, Dairy
(765)494-9478, Email:

Jonathan Townsend, Assistant Professor of Veterinary Clinical Science
(765) 494-0333, Email: