Can You Feed Mouldy Corn as Silage?

US - A lot of this fall's corn crop, especially in the northern Corn Belt, came out of the damp, cool fields infected with one of several types of mould. Some are more harmful than others, but what about when the grain's been ensiled? Does the mould continue to grow and pose a threat to cattle if the corn's fed as silage?
calendar icon 2 December 2009
clock icon 2 minute read

That's the question posed in a recent report by a team of University of Wisconsin Extension dairy scientists and plant pathologists led by dairy science specialist Patrick Hoffman. And, the answer depends a lot on the optimal growing conditions needed for each mould type to thrive.

"Under field conditions, these moulds grow and proliferate under the presence of oxygen, near neutral pH, at high grain moisture and at temperatures of 25 to 50 degrees [Fahrenheit]," Mr Hoffman says of the most common field moulds in Wisconsin, Cladosporium, Diplodia, Gibberella zeae and Fusarium sp.

Now look at what happens when corn's ensiled. First, the pH is reduced by fermentation, typically to around 4.0 to 4.5. On top of that, the process of ensiling deprives the organic matter of oxygen for a time, while temperatures can reach up to 90 degrees.

"Therefore, in concept, field moulds should not continue to grow and produce mycotoxins in storage if pH has been sufficiently reduced and oxygen is not present under ensiled conditions," Mr Hoffman says.

But, just because these conditions have been met doesn't mean the moulds are completely belly-up. How that silage is stored can sometimes restore conditions favorable for mould's growth. If oxygen can permeate the silage or other microorganisms -- which can promote the development of acids and yeasts that can promote mould growth -- are introduced, mould can return.

Opportunities for storage unit induced exposure to oxygen include the following: Holes in plastic silo bags, top surface layers in bunker and tower silos, oxygen permeable silo staves and liners (i.e. mould around the silo wall), poor fitting or silo doors in disrepair, air pockets created by silo bag fillers, air exposure through the hatch of oxygen limiting silos, and oxygen inversion in oxygen limiting silos," Mr Hoffman says. "Storage unit induced oxygen exposure has the potential create oxygen rich micro-environments in the storage unit and field moulds do have the potential to grow and produce mycotoxins in these oxygen rich micro-environments."

While you're inspecting silage storage facilities, keep your eye on the silage itself, as there are visual symptoms of product that's rife for mould and toxin infection.

"High moisture corn in an oxygen rich micro-environment often becomes caked and clumpy and visible mould may be present," Mr Hoffman says. "Obviously mouldy, caked, or discolored high moisture corn should be discarded and not fed to dairy cattle."

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