Some fungi molds in grain can produce harmful compounds called mycotoxins. Pigs consuming mycotoxins above their tolerance level will face health and reproductive problems. Submitting samples of contaminated feeds to the laboratory can help you manage your feeding practices and prevent mycotoxin toxicity in your pigs.
What are mycotoxins?
Certain molds of fungi in grain produce compounds (mycotoxins) that may be harmful to humans or animals. Fungal growth with mycotoxin production can occur during:
- Plant growth
- Processing of grains
Several factors influence fungal growth with mycotoxins.
- Moisture level
- Availability of oxygen
Damaged, immature, drought stricken, or stressed grain is more prone to mold. Molds may reduce the nutrient content and quality of the grain, but the harmful effects of mycotoxins are most concerning.
Scientists have identified 300 to 400 mycotoxins to date. Only a few mycotoxins have shown to cause significant harm to health and performance in pigs fed contaminated plant-based feedstuffs. Harmful mycotoxins include:
- Deoxynivalenol (vomitoxin)
- T-2 toxin
Mycotoxins aren’t present in all moldy grains. The following molds were found to be the most harmful to swine.
- Fusarium fungi
Apergillus flavus produces a variety of aflatoxins (B 1, B 2, G 1, G 2, M 1, M 2). Ideal conditions for producing aflatoxin include temperatures of 82 to 90 degrees F and grain moisture levels of 22 to 26 percent. Alflatoxin occurs in a variety of grains including corn, wheat, barley, and oats. While this mold is more common in the southeastern United States, it has been an occasional problem in the Midwestern corn belt when drought conditions occur.
Aflatoxin is the only mycotoxin regulated by the United States Food and Drug Administration. This is because aflatoxin has been shown to be carcinogenic, and thus concerns exist about the mycotoxin entering the human food chain.
- No more than 20 parts per billion of aflatoxin in contaminated grain is allowed for interstate shipment.
- Grains containing aflatoxin levels over 20 parts per billion can’t be used for human consumption or dairy feeds and shouldn’t be fed to young animals.
- At low levels (20 to 200 parts per billion), aflatoxin decreases performance and well-being. These levels commonly reduce feed intake and result in poor growth rate and immune function.
- At high levels (over 1000 parts per billion), death may occur.
Aspergillus ochraceus and Penicillium viridicatum produce ochratoxin. Similar to aflatoxin, ochratoxin mainly occurs in the southeastern part of the United States. Ochratoxin occurs in corn, wheat, barley and oats. Levels over five parts per million in the diet can
- Harm kidney function
- Cause swelling in the intestine
- Cause fatty liver
- Produce cell death in the lymph nodes
- Cause other disorders
Fusarium graminearum produces deoxynivalenol (vomitoxin) and often occurs on corn (Gibberella ear rot), wheat and barley (Head scab). The mold usually develops during cool, damp weather and results in a white or reddish fungus. It’s most common in the upper midwestern United States and Canada.
- Levels over 1 part per million may reduce feed intake and rate of gain.
- Levels over 5 parts per million results in feed refusal.
- Levels over 10 parts per million may result in weight loss or vomiting.
If you replace contaminated feed with clean, uncontaminated feed, pigs will usually start eating feed without any other visual signs.
Fusarium graminearum also produces zearalenone, a mycotoxin that mimics estrogenic compounds, and thus affects reproductive performance. Zearalenone may occur with vomitoxin in Gibberella ear rot of corn or scabby wheat. But it’s more likely to occur during grain storage than in the field.
Prepubertal gilts are most susceptible to zearalenone. Gilts and sows show
- Vulva reddening and swelling
- Sometimes vaginal and rectal prolapses
- Abnormal estrous cycles
- Reduced litter sizes
When fed 60 to 90 parts per million zearalenone for the first 15 days post-mating, embryo development stops. Not only is the litter lost, but females often won't return to estrus for several months.
Fusarium moniliforme produces fumonisin, a recently identified mycotoxin of concern in swine. Fumonisins can be found in corn-producing areas of the upper midwestern United States. Types B1, B2, and B3 are the most common fumonisins. B1 accounts for about 75 percent of total fumonisin found in grain.
Fumonisin causes pulmonary edema (filling of the lungs with fluid) and weakening of the immune system. In humans, fumonisin harms brain, liver and lung function but is also a carcinogen (see table 1).
Several factors affect the signs and severity of mycotoxin toxicity in pigs.
- Type of mycotoxin
- Level of mycotoxin in the feed
- Age of the pig
- Production phase of the pig
Young pigs and breeding swine are usually the most prone to mycotoxins. In addition, combinations of certain mycotoxins may harm performance more than normally expected for each of the mycotoxin levels evaluated individually. Thus, you should consider this when evaluating feeds. Table 1 shows the mycotoxin tolerance levels of pigs and effects of toxicity.
Table 1. Mycotoxin tolerance levels in pigs from Feedstuffs Reference Issue (1997).
|Mycotoxin||Maximum tolerable level||Comments|
|Aflatoxins (B1, B2, G1, G2)||< 20 ppb for human use, dairy feed, feed for immature animals < 100 ppb for breeding swine < 200 ppb for finishing swine (>120 lbs body weight)||Carcinogenic (can cause cancer) Immunosuppressant (weakens the immune system) Acute signs: Anorexia Depression Ataxia (lose body control) Epistasis Chronic signs: Reduced feed efficiency Reduced milk production Icterus (yellowing of skin) Decreased appetite|
|Zearalenone||< 1 ppm for young growing pigs < 2 ppm for breeding herd < 3 ppm for finishing pigs and young and old boars||Estrogenic effects: Swollen vulvas, vaginal or rectal prolapses in pre-pubertal gilts Enlarged uterus Swollen or twisted uterus Shrunken ovaries In boars: Testes atrophy (waste away) Enlarged mammary glands Decreased fertility|
|Deoxynivalenol (vomitoxin)||< 5 ppm on grain and grain by-products. Vomitoxin contaminated feedstuffs shouldn’t exceed 20% of the diet (< 1 ppm in complete feeds).||Reduced feed intake and weight gain are inversely proportional to concentration of vomitoxin. As one increases, the other decreases High levels cause feed refusal and vomiting|
|T-2 toxin||< 1 ppm||Strong immunosuppressive agent that directly affects immune cells and modifies immune response as a consequence of other tissue damage Frequent defecation, vomiting, weight loss and feed refusal|
|Fumonisin||Not established||Carcinogenic in laboratory tests using rats Associated with pulmonary edema in pigs|
|Ochratoxin||< 200 ppb||Ochratoxin A is most common and potent. Reduced growth Reduced feed efficiency Increased mortality Liver and kidney damage|
|Ergot||< 200 ppb||Vertigo Staggers Convulsions Temporary posterior paralysis Eventual death Decreased peripheral blood supply Reduced growth tail loss Reduced reproductive efficiency of sows|
There are no known methods of detoxifying mycotoxins in contaminated grain. Thus, it’s essential to prevent mycotoxin production by properly storing grains. There are a few ways to reduce the harmful effects of mycotoxins on swine health and performance.
- Feed possibly contaminated feed or grain to a small number of "test" animals and closely watch them for signs of mycotoxin toxicity.
- Prepubertal gilts are often good "test" animals if you suspect the feed contains zearalenone (swollen vulvas) or vomitoxin (reduced feed intake).
- Collect samples of the suspect grain and send them to a commercial analytical laboratory to determine mycotoxin levels. Once you know the levels, you can blend contaminated grain with good quality grain to lessen mycotoxin levels below the critical levels.
- Try marketing the grain to cattle (not dairy cows if aflatoxin contaminated) or sheep producers. Ruminants are less sensitive to mycotoxin toxicity than pigs and poultry. You can then purchase uncontaminated grain to avoid health and performance problems.
- Consider putting grain through a grain cleaner to remove fines. Broken and damaged kernels are generally highest in mycotoxin contamination because the seeds natural protection has been broken. Avoid feeding grain screenings and fines to swine.
- Sodium bentonite and a commercial feed additive called NovasilTM can reduce the harmful health and performance effects of pigs fed aflatoxin-contaminated feeds. They may also partially lessen the harmful effects of other mycotoxins.
- Dry and aerate grains to adequate moisture levels before storing to prevent further mold growth and mycotoxin production. Consider adding commercially available additives or organic acids (propionic, fumaric, citric) to prevent mold growth.
- Avoid feeding mycotoxin-contaminated grain to the breeding herd and young pigs.
- Grow-finish pigs fed for slaughter tolerate mycotoxin-contaminated grain best.
If you notice clinical signs of mycotoxin toxicity, it’s important to properly collect a grain or feed sample and send it to the laboratory. The laboratory can determine the presence and level of possible mycotoxins. Sampling accounts for 80 to 90 percent of the error related to measuring mycotoxins in grain or feed.
Collect random samples (10 to 30) from several areas within a batch of grain or feed.
If possible, use a grain probe at several evenly spaced out locations for the most representative sample.
You can collect samples periodically from grain being augered for effective sampling.
Combine these samples and submit the composite sample to the laboratory.
Use paper bags to transport samples. Plastic bags can collect water and promote additional fungal growth.
Analytical tests for mold spore counts are of little or no value.
Contact the laboratory for specific sampling requirements prior to submission.
Reviewed in 2018