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¶ Introduction
“Mycotoxins” are poisonous compounds or toxins that may be produced by various fungi. More than four hundred individual mycotoxins have been identified, but only a small number of them affect agricultural activities. “Aflatoxin” refers to the mycotoxins produced by some strains of the Aspergillus fungus. Scientists discovered in 1961 that a previously unidentified ailment called “Turkey X disease” was actually caused by the Aspergillus flavus toxins found in peanut meal. They coined the word “aflatoxin” from the cause of the disease (A. flavus toxin –> “a‐fla‐toxin”).
¶ A. What is “aflatoxin”?
- Are group of mycotoxins produced by some Aspergillus fungus strains
- Includes species: Aspergillus flavus, Aspergillus parasiticus, Aspergillus nomius
- Four most common aflatoxins identified as B1, B2, G1, and G2
- Considered potent human carcinogens (cancer‐causing agents)
- Aflatoxin occurs naturally
- Known as “unavoidable contaminants”
- Cannot be completely eliminated from feedstuffs or food
- Consuming small amounts over lifetime presents little risk to health
- Aflatoxin B1
- Produced by Aspergillus flavus
- Mold that grows on oil‐rich grains ii. Especially corn, peanuts and cottonseed
- Most potent of aflatoxin group (B1, B2, G1, G2)
- Can affect cattle, poultry, and humans
- When animals consume feed containing aflatoxin B1
- First, metabolized to aflatoxin M1 in the liver
- Then, excreted in the bile, urine, and milk
- Aflatoxin M1 concentrations in milk usually 1.7% of B1 concentrations of ingested feed
- Produced by Aspergillus flavus
¶ Table 1. FDA Action Levels for Aflatoxin in Grains, Grain by‐Products, and Animal Feeds (Concentrations on Dry Matter Basis).* |
|
| CORN and CORN PRODUCTS intended for: | Action level |
| Beef cattle, finishing (i.e., feedlot) | 300 ppb |
| Beef cattle, breeding animals | 100 ppb |
| Dairy animals | 20 ppb |
| Swine, finishing (100 lb. or greater) | 200 ppb |
| Swine, breeding animals | 100 ppb |
| Immature animals | 20 ppb |
| Poultry, mature | 100 ppb |
| Animal species not specified above | 20 ppb |
| COTTONSEED MEAL intended for: | Action level |
| Beef cattle (regardless of age or breeding status) | 300 ppb |
| Dairy animals | 20 ppb |
| Swine (regardless of age or breeding status) | 300 ppb |
| Poultry (regardless of age or breeding status) | 300 ppb |
| Animal species not specified above | 20 ppb |
| PEANUTS and PEANUT PRODUCTS intended for: | Action level |
| Beef cattle, finishing (i.e., feedlot) | 300 ppb |
| Beef cattle, breeding animals | 100 ppb |
| Dairy animals | 20 ppb |
| Swine, finishing (100 lb. or greater) | 200 ppb |
| Swine, breeding animals | 100 ppb |
| Immature animals | 20 ppb |
| Poultry, mature | 100 ppb |
| Animal species not specified above | 20 ppb |
| OTHER FEEDS and FEED INGREDIENTS intended for: | Action level |
| Dairy animals | 20 ppb |
| Immature animals | 20 ppb |
| Animal species not specified above | 20 ppb |
| *Micrograms per kilogram (µg/kg) is equivalent to parts per billion (ppb) | |
¶ B. Aflatoxin “action levels”
- 1. Levels set by U.S. Food and Drug Administration (FDA)
- “Action levels and tolerances represent limits at or above which FDA will take legal action to remove products from the market.”
- Depends on commodity and animal type (see Table 1)
- Upper limit of 20 ppb (parts per billion) set for food products
- Equivalent to one kernel of corn in 625 bushels
- Milk has aflatoxin M1 action level of 0.5 ppb
- Action level of 20 ppb for feed products intended for dairy rations
- Concentration of individual ingredients must not exceed 20 ppb
- Even if blended ration has 20 ppb or less
- Deliberate blending to dilute toxin levels is illegal
¶ C. Aspergillus ear rot
- Gray‐green, yellow‐green, olive‐green powdery mold.
- Usually develops around injuries
- Associated with damaged kernels
- Most common in hot dry years
- Can grow at temperatures from 45 to 120°; moisture from 15% to 30%
- Can grow at higher or lower temperatures o moisture levels and not produce aflatoxin
- Can grow at temperatures from 45 to 120°; moisture from 15% to 30%
¶ Figure 1. Aspergillus Ear Rot of Corn
¶ D. Conditions favoring aflatoxin production
- Just because visible molds are present, aflatoxin may or may not be present
- A. flavus can grow and produce aflatoxin in almost any organic substrate if conditions are right
- Factors that initiate aflatoxin formation are not well understood
- A. flavus grows most rapidly when:
- Temperatures are between 80° and 100°F
- Relative humidity is greater than 80% to 85%
- Equivalent to:
- 16% to 18% grain moisture in corn
- 8% to 10% grain moisture in peanuts
- Equivalent to:
- Stress factors encourage mold growth and aflatoxin production
- Prolonged drought
- Close planting
- Weed competition
- Low soil fertility
- Insect damage
- Insects carry and transmit spores ii. Can infect living plant tissue or damaged kernels
- Aflatoxin contamination
- Affects corn, peanuts, and cottonseed
- Corn probably commodity of greatest concern
- Corn grown in warm, humid climates likely to have perennial aflatoxin contamination.
- Southern US weather clearly promotes aflatoxin formation more often than Corn Belt weather
- Becomes a concern in stored corn
- When grain temperatures exceeding 77°F
- When grain moisture greater than 16%
- Can appear within 24 to 36 hours after storage
- Can start forming after six to eight hours in wet corn stored in trucks or holding bins
- Inhibited with grain moisture contents less than 12% to 13%; grain temperatures below 55°F
- Concentration never decreases in storage; increases or stays the same
- Affects corn, peanuts, and cottonseed
¶ E. Aflatoxin effects
- Effect on animal health may be acute or chronic
- Aflatoxin poisoning called “aflatoxicosis”
- Acute: death can occur if livestock consume high doses of aflatoxin
- Chronic: more subtle health problems
- Are most common ii. Can result from sub‐lethal doses of aflatoxin iii. Reproduction in swine not primarily affected
- Liver is primary target
- Abnormal blood clotting, hemorrhaging ii. Reduced immune response iii. Degeneration of liver
- Chronic symptoms:
- Reduced growth rate, gains
- Lower milk production
- Decreased appetite
- Reduced feed efficiency
- Poorer carcass quality
- Lower disease resistance, vaccine immunity
- Example: aflatoxin levels over 100 ppb
- May not be fatal to dairy cattle
- Can affect kidney function and overall performance
- Livestock types affected differently
- Dairy and beef cattle are more susceptible to aflatoxicosis than sheep.
- Young animals are more susceptible than mature animals
- Pregnant and growing animals are less susceptible than young animals but more susceptible than mature animals
¶ F. Sampling for aflatoxin
- Survey fields before harvest
- From dent through to harvest, check five to ten field locations
- Target areas with plants that appear most stressed.
- Peel back the husks of 10 ears at each location and inspect for mold
- Olive‐green powdery mold is characteristic of Aspergillus ear rot and potential aflatoxin problems
- If more than 10% of corn ears in a field have more than 10% to 20% mold – harvest ASAP
- Accurate sampling is difficult
- Contamination can vary widely within a field or a storage facility
- Often “kernel‐by‐kernel” situation
- e.g., a few kernels have very high levels (several thousand times the average); most have none
- Aflatoxin in storage bin may only be found in clumps of grain held together by mold growth
- May have been mixed throughout grain mass during transfer
- Suggested sampling procedures
- Standing grain: Collect 25 ears or heads at random throughout the field
- Grain cart/truck: Take multiple probes for a composite 10 lb. sample
- Moving grain stream: Take a composite 10‐lb sample consisting of 12 to 20 subsamples from the grain stream
- Silage: Collect 8 to 12 subsamples to form a 2‐quart to 3‐quart sample during harvest or from storage
- Keep samples cool, but do not freeze
- Ship promptly, early in the week, to avoid weekend delays
¶ G. Interpreting laboratory results
- Analytical methods
- Black light (ultraviolet)
- Screening for aflatoxin only ii. 40% to 60% false positives
- Enzyme‐linked immunosorbent assay (ELISA)
- Coupling reaction between specific mycotoxin and antibodies specific for that mycotoxin
- Test kit: screening test to provide yes/no answer
- Test kit with reader: provides quantitative data
- High performance liquid chromatography (HPLC)
- Can test all mycotoxins
- More sensitive; provides quantitative data at lower detection limits than ELISA
- Requires more time; more expensive
- Black light (ultraviolet)
- Interpretation depends on commodity and animal type (see Table 1)
- Data may be ± 25% to 40% of reported value due to typical sampling and analytical error
- Official grain inspection certificate
- Not everyone can or should always have their grain officially inspected
- Certificate can only be issued by partners of official system FGIS system field offices and State and local agencies authorized by FGIS
¶ References
Adams, R.S. et. al. Mold and mycotoxin problems in livestock feeding. DAS 93‐21. Pennsylvania State Univ. Coop. Ext. Svc. 17 pg. http://www.das.psu.edu/research‐extension/dairy/nutrition/pdf/mold.pdf/view?searchterm=mycotoxin
Cassel, E.K., S.M. Barao, and D.K. Carmel. 1989. Aflatoxicosis and Ruminants. Fact Sheet 507. Univ. of Maryland. Coop. Ext. Svc., College Park MD. 2 pg.
Carlson, M.P., S.M. Ensley, R.J. Grant, and D.R. Smith. 2002. Aflatoxin M1 in Milk. Univ. of Nebraska Coop. Ext. Svc. 3 pg. http://www.adiveter.com/ftp/articles/articulo747.pdf accessed 08/04/11
Cornell Univ., Dept. of Animal Science. Aflatoxins: Occurrence and Health Risks. http://www.ansci.cornell.edu/plants/toxicagents/aflatoxin/aflatoxin.html accessed 08/04/11
EHSO. 2011. Aflatoxins in Your Food ‐ and their Effect on Your Health. Envionment, Health, and Safety Online, Atlanta GA. http://www.ehso.com/ehshome/aflatoxin.php accessed 08/05/11.
Hurburgh, C.R. Mycotoxins in the Grain Market. Integrated Crop Mgmt. News. Iowa State University Extension. http://www.extension.iastate.edu/Grain/Topics/MycotoxinsintheGrainMa rket.htm accessed 11/1/2009
Krenzer, E. 1979. Aflatoxins in corn. Crops & Soils. October 1979. pg 11‐12.
Robertson, A. 2012. Aspergillus Ear Rot and Aflatoxin Production. Integrated Crop Mgmt. News. Iowa State University Extension. http://www.extension.iastate.edu/CropNews/2012/0801robertson.htm.
Texas Agric. Ext. Svc. 1998. . Texas Drought Management Strategies: Aflatoxins and Dairy Cattle. rev. 01 Aug 1998. http://agnewsarchive.tamu.edu/drought/drghtpak98/drght30.html accessed 08/04/11
National Feed and Grain Assn. 2016. NFGA Alert: Mycotoxins. https://imis.ngfa.org/images/uploads/NGFA‐Alert‐MycotoxinsSept282016‐FINAL.pdf accessed 11/18/2019.
USDA. 2009. Inspecting Grain: Practical Procedures for Grain Handlers. USDA‐Federal Grain Inspection Service, Washington DC. 83 pg
Wysong, D. 1981. Aflatoxins: What are they and why do they occur? Crop Protection Clinic Proc., Univ. of Nebraska Coop. Ext. Svc. pg. 119‐125.