Effect of mycotoxins in swine
What are mycotoxins?
Mycotoxins are compounds produced in grain by specific molds or fungi as secondary metabolites that may or may not be toxic to humans or animals. Fungal infestation and subsequent mycotoxin production can occur during plant growth, maturity, harvesting, storage, and processing of grains, and is influenced primarily by moisture level, temperature, and availability of oxygen. In addition, grain that is damaged, immature, drought stricken, or otherwise stressed is more susceptible to mold growth. Molds may reduce the nutrient content and quality of the grain, but the toxic effects of metabolites are generally of primary concern.
Scientists have identified 300 to 400 mycotoxins to date, but only a few have been shown to cause significant, detrimental health and performance problems in swine fed contaminated plant based feedstuffs. These include aflatoxin, deoxynivalenol, zearalenone, fumonisin, ochratoxin, ergot, and T-2 toxin. It is important to remember that the presence of molds in grains does not automatically indicate mycotoxin presence. Aspergillus, Penicillium, Claviceps, and Fusarium fungi have been identified as producing the mycotoxins most detrimental to swine.
There are a variety of aflatoxins (B 1, B 2, G 1, G 2, M 1, M 2) produced by Apergillus flavus. Temperatures of 82° to 90° F, along with grain moisture levels of 22% to 26% provide ideal conditions for producing aflatoxin in a variety of grains, including corn, wheat, barley, and oats. The mold is abundant in the southeastern United States, but has occasionally become a problem in the Midwestern corn belt when drought conditions occur.
Aflatoxin is the only mycotoxin regulated by FDA because it has been shown to be carcinogenic, and therefore concerns about the mycotoxin entering the human food chain exist. No more than 20 ppb aflatoxin is allowed for interstate shipment of contaminated grain. Grains containing aflatoxin levels in excess of 20 ppb cannot be used for human consumption and dairy feeds, and should not be fed to young animals. At low levels (20 – 200 ppb), aflatoxin decreases performance and well-being. Feed intake is commonly reduced, resulting in depressed growth rate, while immune function is suppressed. At high levels (1000 ppb +), death may occur.
Ochratoxin mycotoxins may be produced by Aspergillus ochraceus and Penicillium viridicatum. Similar to aflatoxin, ochratoxin primarily occurs in the southeastern portion of the United States, and has been found in corn, wheat, barley, and oats. Concentrations greater than 5 ppm in the diet can impair kidney function, cause enteritis and fatty liver, and produce necrosis of lymph nodes along with a variety of other pathological conditions.
Deoxynivalenol (DON) is commonly known as vomitoxin. The mycotoxin is produced by Fusarium graminearum that often occurs on corn (Gibberella ear rot) and wheat and barley (Head scab). The mold commonly develops during cool damp weather, resulting in a white or reddish fungus, and is most common in the upper Midwestern United States and Canada. Levels above 1 ppm may reduce feed intake and subsequent rate of gain. Concentrations above 5 ppm result in feed refusal, and above 10 ppm may result in weight loss. Vomiting in pigs may also be observed at levels of 10 ppm or more. When contaminated feed is replaced with clean, uncontaminated feed, pigs will generally resume consuming feed with no other visual signs apparent.
Zearalenone, also produced by Fusarium graminearum, is a mycotoxin that mimics estrogenic compounds, thus affecting reproductive performance. Zearalenone contamination may occur with DON with Gibberella ear rot in corn or scabby wheat, but is more likely to occur during storage of the grain rather than in the field. Prepubertal gilts are most susceptible contamination. Gilts and sows exhibit vulva reddening and swelling, while vaginal and rectal prolapses may also occur with zearalenone consumption. Irregular estrous cycles and reduced litter sizes are also commonly observed. When fed 60-90 ppm zearalenone the first 15 days post-mating, embryo development is stopped. Not only is the litter lost, but females often won't return to estrus for several months.
Fumonisin, produced by Fusarium moniliforme, has only recently been identified as a mycotoxin of concern to swine production. Fumonisins can be found in corn-producing areas of the upper midwestern United States. Types B1, B2, and B3 are the most abundant fumonisins found, with B1 accounting for approximately 75 percent of total fumonisin content. Pulmonary edema, or filling of the lungs with fluid, has been reported with fumonisin toxicity in swine, along with weakening of the immune system. Fumonisin has also been identified as a carcinogen in humans, in addition to adversely affecting brain, liver, and lung function.
Maximum tolerable mycotoxin levels in swine diets
The types of signs exhibited and degree with which swine are affected by mycotoxicosis, or mycotoxin toxicity, is largely affected by not only the type of mycotoxin and concentration in feed, but also by the age and phase of production of the pig. Young pigs and breeding swine are generally the most susceptible to mycotoxins. Additionally, combinations of certain mycotoxins may produce elevated negative effects on performance above that normally expected for each of the mycotoxin levels evaluated individually, and therefore must be considered.
|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. Immunosuppressant. Acute signs: anorexia, depression, ataxia, epistasis. Chronic signs: reduced feed efficiency, reduced milk production, icterus, decreased appetite.
< 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, enlarged mammary glands, decreased fertility.|
|Deoxynivalenol (vomitoxin)||< 5 ppm on grain and grain by-products. DON contaminated feedstuffs should not exceed 20% of the diet. (< 1 ppm in complete feeds)||Reduction in feed consumption and weight gain are inversely proportional to concentration of DON. High concentrations cause feed refusal and vomiting.|
|T-2 toxin||< 1 ppm||Potent 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.|
< 5 ppm (extrapolated from horse data)
|Carcinogenic in laboratory tests using rats. Associated with pulmonary edema in pigs.|
|Ochratoxin||< 200 ppb has been associated with kidney damage in swine||Ochratoxin A is most common and potent. Reduction in growth, 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.|
aFeedstuffs Reference Issue (1997)
Management strategies for utilizing mycotoxin contaminated grain
Once grain is contaminated with mycotoxins, there are no known methods of detoxifying the mycotoxins. Therefore, prevention of mycotoxin production by ensuring proper environmental conditions during storage is essential. However, there are a few management strategies that can be used to minimize the negative effects of mycotoxins on swine health and performance. These include:
- Feed the suspect feed or grain to a small number of "test" animals and closely watch for symptoms of mycotoxicosis. Pre-pubertal gilts are often good "test" animals when checking suspected feed for zearalenone (swollen vulvas) and vomitoxin (reduced feed intake).
- Collect samples of the suspect grain and send to a commercial analytical laboratory for determination of levels of mycotoxins. Once the levels are known, contaminated grain can be blended with good quality grain to dilute the concentration of mycotoxins below critical levels.
- Try marketing the grain to cattle (not dairy cows if aflatoxin contaminated) or sheep producers. Ruminants are less sensitive to mycotoxicosis than pigs and poultry. Uncontaminated grain can then be purchased to avoid health problems and performance reductions.
- 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 have been shown to be effective in minimizing the adverse health and performance effects of pigs fed aflatoxin contaminated feeds. They may also have some benefit in partially alleviating negative effects from other mycotoxins.
- Be sure that stored grain is dried and aerated to recommended moisture levels 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 the breeding herd and young pigs. Grow-finish pigs fed for slaughter are the best candidates for tolerating mycotoxin contaminated grain.
Testing for mycotoxins in grains or feeds
If clinical signs of mycotoxicosis are observed, it is important to properly collect a grain or feed sample and send it to a laboratory to determine the presence and level of the suspected mycotoxin(s). Sampling accounts for 80 – 90% of the error associated with measuring mycotoxins in grain or feed. Analytical tests for mold spore counts are of little or no value. Random samples (10 to 30) should be collected from several locations within a batch of grain or feed and combined to provide a composite sample for submission. Using a grain probe at several evenly distributed locations will provide the most representative sample. Samples can also be collected periodically from grain being augured can also be an effective form of sampling. Paper bags should be used to transport sample(s), since plastic bags retain moisture, and therefore can promote additional fungal growth. A partial list of laboratories in the immediate Minnesota area offering mycotoxin testing is provided below. Contact the laboratory for specific sampling requirements prior to submission.
Van Es Laboratories
North Dakota State University
Fargo , ND 58105
Minnesota Valley Testing Laboratories, Inc.
1126 North Front Street
New Ulm , MN 56073
P.O. Box 188
Hwy 17 North
Eagle Grove , IA 50533
Woodson-Tenent Laboratories, Inc.
Des Moines , IA