Molds and Mycotoxins

By Steve Merriam, Vice President, Animal Care Brand Manager and Bruce Arentson, V.P., Regulatory Affairs, Equine & Companion Animal Nutritionist

This year (2009) continues to be an economic challenge to agriculture but fall has brought another serious obstacle for farmers; cool and wet weather for harvest.  It has been nearly impossible to get into the fields and, if one is that lucky, moisture levels in the corn are generally in the 30-33% range.  Along with these two challenges comes a third, mold and mycotoxins.  The presence of mold (fungus) does not necessarily mean that toxins are present in amounts to cause issues within livestock.  However, in today’s environment, mycotoxin screens, and if needed, mycotoxin analyses need to be conducted.

The attached series of tables and information was derived from an Ohio State University (OSU) website that is a cooperative effort of numerous land grant universities.  Table 1 summarizes the main mycotoxins that affect livestock production.  Species, mycotoxin, upper limit of safety and their effects are noted.

Also, included in this OSU document are preventative practices, pre-harvest and post-harvest, as well as treatments.

Kent Feeds offers mycotoxin adsorbent in Dynasty® and Granolene® equine products; Kent Integral™ 40 for multi-species equine, cattle, poultry, and swine; FeverGuard® MTB-100® for dairy; and several custom order products.  The effective level of mycotoxin adsorbent in the product is dependent on the feed directions (consumption) of the product. 

Moldy Grains, Mycotoxins And Feeding Problems

Preventive Practices
Prevention is the best method to control mold growth and possible toxin formation.  The following practices can help minimize mold growth and subsequent toxin production in storage:

Pre-harvest:

  • Clean inside and outside of grain bins and dryers.
  • Prior to storage, check the condition of the bin for possible water leaks, and clean it properly by removing dust, dirt, leftover grain and other foreign material.
  • Crop rotation in many regions or tillage can reduce the risk of Gibberella ear rot in corn and Fusarium head blight of wheat.  These practices have little effect on other corn ear rots.
  • Some corn hybrids are more resistant to ear rots than others, but overall, resistance to ear rots is not widely available. Some Bt hybrids, those that produce BT in the kernels, have less ear rot due to insect control resulting in less toxin problems.
  • Control of second generation European corn borers and other insect pests of corn ears can greatly reduce infection by Fusarium and Aspergillus.
  • Few wheat varieties have high levels of resistance to Fusarium head blight (scab).  Plant moderately resistant varieties when available.  Planting several varieties that differ in maturity will reduce the risk of disease to the whole crop.
  • As with any crop pest, early detection through scouting and early harvest can reduce serious losses and avoid crises.  Decisions on handling moldy grain should be made before it is harvested.  After harvest, spoilage can occur quickly if delays result from indecision.
  • If extensive ear rot development is observed (10% or more of the ears with more than 10-20% mold), the field should be harvested as soon as moisture content reaches a level that can be harvested.  Even if some drying costs are incurred, this will be less expensive than loss of crop value due to mycotoxins and resulting feeding problems.

Post-harvest:

  • The crops should be allowed to mature in the field to the following moisture contents: shelled corn, 23-25%; ear corn, 20-25%; small grain, 12-17%; and soybeans, 11-15%.
  • Harvesting equipment should be adjusted to minimize damage to seeds or kernels and allow for maximum cleaning.  Cracked or broken seeds or kernels are more susceptible to mold invasion.
  • Upon storage, dry the grain to 13-14%, if possible, within 48 hours.  Long-term storage can be achieved at a uniform moisture of 18% for ear corn; 13% for sorghum, wheat and shelled corn; and 11% for soybeans.
  • After drying, store under cool temperatures (36-44° F).
  • Every few weeks check the condition of the grain for temperature, wet spots and insects.

Grain Treatments:

  • Antifungal treatments can be applied to grain to reduce mold growth in storage.  These products, such as proprionic acid, do not kill the mold already present nor do they reduce toxins already present in the grain.  Do not use antifungal agents on stored grain unless you are certain the grain can be marketed after treatment.
  • Hydrated sodium calcium aluminosilicate (HSCAS) (Novasil) can reduce the effects of aflatoxins when fed to swine, cattle, or poultry. HSCAS at 10 lb./ton provides substantial protection against dietary aflatoxins.

Testing for Mycotoxins:

  • The presence of a fungus known to produce toxins is not proof that the grain contains injurious levels of toxin.
  • It may be a good investment to collect a representative sample and send it to a laboratory for chemical analysis.
  • The first step in mycotoxin determination is sampling of the grain.  Particular attention should be given to the sampling procedure because sampling error will be the greatest source of variation in the analytical procedure.  This variation is primarily due to the uneven distribution of the mycotoxin contaminated kernels within a lot of grain or feed.  The ideal sampling procedure should assure the highest probability of detecting mycotoxins even when contamination is low.
  • One method of sampling grain is to use a probe sampler.  Since mold growth usually occurs in spots in the grain lot, best sampling is done on recently blended lots of grain.
  • Another method is to collect small samples from the moving stream of grain as it is moved in or out of the bins.  With both sampling methods, the collected grain is pooled into a large aggregate sample that represents the lot.
  • For shelled corn, it is recommended that the aggregate sample be about 10 pounds.  The aggregate sample should be coarsely ground.  Most analytical procedures need only about 25 grams (0.9 ounces) of ground corn, so it is important that the aggregate sample be thoroughly mixed after grinding.  A one or two pound sub-sample is then taken and it is more finely ground.  From this sub-sample a final sample is taken for analysis.
  • A number of commercial, university and government laboratories perform mycotoxin analyses for a fee.  Contact the lab to determine the proper way to obtain and ship the sample.  For general information see:(http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/mycotoxin%20text2.htm).
  • Blending is not an approved practice by the FDA for interstate commerce.  Blending is a practice intended to reduce toxins to acceptable levels in small lots only for on farm use.
  • If the mycotoxin in the contaminated feed is known, it may be a good idea to channel the feed to animals that are more tolerant.

Table 1

Mycotoxins
Reported Detrimental Feed Concentrations

Zearalenone (ppm=parts per million)

Swine

Concentration

Duration

Effect

Prepubertal gilts 1-5 ppm 3-7 days Hyperestrogenism, prolapse
Sexually mature open gilts  3-10 ppm Mid-cycle (day 11-14)  Anestrus, pseudopregnancy
 Bred sows  15-30 ppm  1st trimester Early embryonic death, small litters
Juvenile boars 10-50 ppm Indefinite Reduced libido, small testicles
Mature boars 200 ppm Indefinite No effect
Cattle
Virgin heifers 12 ppm Open Heifers Reduced conception
Dairy cows 50 ppm Open cows Reduced conception
Poultry
Broilers & turkey poults  200 ppm  Indefinite  No effect
 

Deoxynivalenol (vomitoxin, DON)

Swine
Feeder pigs 1-3 ppm 1-5 days Reduced feed intake
Feeder pigs 5-10 ppm 1-5 days 50% reduction in feed intake, vomiting
Feeder pigs 10-40 ppm 1-5 days Complete feed refusal, vomiting
 Sows  3-5 ppm Gestation, lactation  Lower fetal weights, or no effect
Cattle
Feeder cattle 10 ppm Indefinite No effect
 Dairy cows  6 ppm  6 weeks No effect or slightly reduced feed intake
Dairy cows 12 ppm 10 weeks No effect on milk production
Poultry
Broilers and turkey poults  50 ppm  Indefinite  No effect

 Table 1 (Continued)

 

Fumonisins (FB1 and/or FB2)

Horses Concentration Duration Effect
 All classes and ages  >10 ppm  30 days Liver damage, leucoencephalomalacia, death
Swine
 All classes and ages  >25 ppm  30 days Reduced gain and feed efficiency, mild liver damage
  All classes and ages   >50 ppm   10 days Reduced gain and feed efficiency, moderate liver damage
All classes and ages >100 ppm 5 days Severe pulmonary edema, death
Cattle and sheep
 All classes and ages  >100 ppm  30 days Slightly reduced gain, mild liver damage
 All classes and ages  >200 ppm  14 days Reduced feed intake and gain, moderate liver damage
Turkeys
  All classes and ages   >100 ppm   7-21 days Reduced feed intake, liver damage, diarrhea, rickets, tibial lesions
Chickens
  All classes and ages   >200 ppm   7-21 days Reduced feed intake, liver damage, diarrhea, rickets, tibial lesions

FDA’s guidance level for total fumonisins in corn and corn by-products (not to exceed 20% of the diet) used for equine and rabbit feed products is 5 ppm (1 ppm in finished feed). 

Table 1 (Continued)

 

Aflatoxins (ppb=parts per billion)

Swine Concentration Effect
 All classes and ages  200 ppb Slow growth, reduced feed efficiency
 All classes and ages  400 ppb Liver damage and immune suppression
Feeder Cattle
All classes and ages 400 ppb Tissue residues
 All classes and ages 700 ppb Mild liver damage, reduced growth and feed efficiency
 All classes and ages  1000 ppb Moderate liver damage and weight loss
All classes and ages  2000 ppb Severe liver damage, jaundice, death
Dairy Cows
Lactating cows 20 ppb Detectable aflatoxin in milk
Lactating cows 1500 ppb Decreased milk production
Poultry
Broiler chicks 210 ppb No effect 
Turkeys 250 ppb Reduced growth
 Broiler chicks  420 ppb Lose weight, moderate liver damage after 3 weeks
Horses
 All classes and ages  400 ppb Liver damage and immune suppression
Munkvold, G., Osweiler, G., Hartwig, N. 1997 Iowa State University Ext. PM-1698

FDA has set a maximum limit of 20 ppb for aflatoxins in commercial grains used in feed for immature animals, dairy animals, poultry, horses and turkeys, and for unknown use.