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Feed Considerations During a Wet Year: Molds and Mycotoxins

 

In stark contrast to last year, where drought conditions in spring caused concern about feed quantity, excessive moisture this year has led to concerns about feed quality, especially in grains and stockpiled forages. High moisture during the growing season and at harvest increases the chance of fungal and mold growth in both hay and cereals. Fungi and molds reduce the nutritive value of a feedstuff and can produce toxins that have a significant impact on animal health and performance.  So whether purchased or home grown, it is important to consider the possibility of mycotoxins in your feed.


Ergot

Ergot is a fungal disease of plants that occurs during wet growing conditions. It is caused by the fungus Claviceps purpurea.  Ergot can overwinter and germinate in the spring. It infects a plant during the flowering stage, and the ergot bodies replace the seed kernels of the plant.

Susceptible plants (in order of susceptibility) are:  rye>triticale>wheat>barley>grasses>oats

Toxicity occurs due to ingestion of ergot alkaloids. Ergotism has a long history, being associated with the Salem witch hunts of 1691, due to its effect of mania and psychosis in people.

hindlimb lesions

In cattle, signs of ergot poisoning can include:

  • hind limb lameness
  • sloughing of ears, feet, tips of tails (gangrenous form)
  • reduced milk production
  • excitability, belligerence (nervous form, not common in cattle)

​It can take 2 to 8 weeks for these signs to become apparent.

Ergot can be highly concentrated in grain screenings, therefore, producers feeding by-product feeds need to ensure products have been tested for ergot levels.

  • Recommended maximum levels are <0.1% DM ( < 200 ppb of total ergotoxin)
  • Most grain processing terminals visually inspect for ergot, but this does not indicate toxin level.

**If you have ergot in your feed, it is important to know the toxin levels and appropriately dilute out the concentration with another feed source.

Ergot on pasture is difficult to manage, and you must intensively graze or mow pastures to ensure plants do not flower.


Fusarium

Fusarium is another fungal disease of cereals that is particularly exacerbated during wet growing conditions. It occurs primarily in wheat and corn, but can also affect barley, rye and oats. Fusarium reduces quality grade and protein levels in cereals, resulting in an abundance of feed grain available to beef producers (4% Fusarium by weight is allowable for feed wheat, compared to 0.25% for No.1 wheat.)

Fusarium produces a number of mycotoxins that can be dangerous to human and animal health. These toxin levels peak in the kernel prior to maturity, so testing of green feed and silage is important.

DON (and other Trichothecenes)

  • the most common mycotoxin associated with fusarium in Canada

  • zero tolerance in malting barley

  • not affected by processing

  • cattle will go off feed, have depressed immunity, increased risk for displaced abomasum, ketosis, and diarrhea

  • maximum tolerated level in beef cattle (dairy) is 5 ppm (1ppm) *

  • many elevators have the capability to measure DON concentration in grain

Zeralenone

  • common in corn

  • estrogenic

  • swine problem

  • may affect reproduction (estrus) in cattle at 4-7 ppm

  • safe at 0.15 ppm in total ration*

Fumonsin

  • very toxic to horses, causes brain lesions

  • limit in feed is 5 ppm in horses, 10 ppm for swine, 50 ppm for cattle*

*on a DM basis

If hay is baled at > 15% moisture, the chance for heating and molding increases. At the very least, mold in a forage will cause a reduction of TDN and palatability. In fact, it is suggested that the energy value of a moldy forage be reduced by 5% when formulating rations for cattle. Moldy forage can cause respiratory diseases in livestock such as fungal pneumonia, or can produce mycotoxins that are dangerous to livestock if consumed in large amounts. 


Aspergillius

Aspergillus is a fungus that can be found in both spoiled hay and grain. It produces two toxins, Ochratoxin and Aflatoxin. Young animals are most susceptible, and the toxins can be passed through the milk. The liver is the target organ for these toxins.

 Signs of Aspergillius toxicity include:

  • mycotic abortion
  • reduced growth and feed efficiency at levels 150-400 ppb
  • death at levels > 600 ppb in young and 1000-2000 ppb in mature cattle


Moldy sweet clover

The toxic compound associated with moldy sweet clover is dicoumarol, which acts to prevent blood clotting.

Signs of dicoumarol toxicity can include:

  • abortion
  • death of young calves
  • profuse bleeding in animals of all ages

Testing

Most of the toxicities discussed above rely on accumulation of the toxin over time. As such, mycotoxins in feed can be managed by dilution with clean feed. In order to do this, you must know the concentrations of these toxins in your feed, which can be accomplished with testing.

Testing for mycotoxins requires multiple sub-samples to be taken in order to get the best representation of mycotoxin levels, and a specified sampling method is required.

Please ask your veterinarian or nutritionist about proper sampling techniques!

As always at SWAHC, we are happy to answer any questions you may have and assist you with feed testing!

Written by: Dr. Brittany Wiese

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