Moldy Silage - Frequently Asked Questions

Why does moldy silage and feed exist?
All feeds contain microbial contaminants. Some types of bacteria, fungi, and molds can grow and multiply resulting in poor quality feed when environmental conditions are not optimal for storage. Not all molds are toxic but those that produce mycotoxins are, and may cause decreased productivity or create animal health concerns.

When does moldy silage occur?
Silage is a fermented forage or feedstuff. When the crop is cut, packed and sealed, the fermentation process begins and continues for 2 to 4 weeks until the pH stabilizes. Cereal silage should have a pH of 4.2 to 4.6 and legume silage should have a pH of 4.5 to 5.0 when properly ensiled.

If silage is not properly sealed to exclude oxygen, complete fermentation cannot occur. Most microbial contaminants grow in an aerobic environment. If air is allowed to enter the silage during fermentation spoilage occurs.

Excessive moisture content in silage prevents a rapid pH drop in the silage allowing a longer period of time for spoilage to occur. Many of the spoilage microbes cannot live in a strongly acidic environment.

How does spoilage influence feed quality?
When silage smells musty or moldy, extensive nutrient and dry matter losses can be expected. The silage may be very unpalatable to the cattle. If you see 1 inch of spoiled silage on the top of the pit, this relates to 4 to 6 inches of packed silage loss.

If the silage smells rancid or rank, it is a good indication that the silage was too wet when harvested and took a long time to ensile. If temperatures remained above 400C for a period of time protein availability is reduced and considerable amounts of energy were lost.

How will feeding moldy Silage Affect performance?
Feeding moldy forages can cause abortions. It is very difficult to diagnose the exact cause of these mycotic abortions. In some cases sending a silage sample in for microbial analysis may indicate the possible cause of the abortion.

Toxins in moldy feeds enter the bloodstream and the pregnant uterus. The toxins that cause abortions can also cause infertility during the next breeding season.

The secondary effect of moldy feed toxins is a reduction in productivity. These toxins make the animal more susceptible to infections and other diseases. If large amounts of moldy feed are fed it can cause severe diarrhea, loss of appetite, muscular tremors, pneumonia, allergic reactions and death.

What percentage of the ration can be moldy and can it be fed?
A feed test is required to determine feeding value of the silage. Consult with a nutritionist to determine safe feeding levels. If the spoilage is very severe it may be necessary to discard some or all of the silage.

Moldy Feed and Reproductive Failure in Cows
Storage Life of Livestock Feeds - FAQ
Managing Cattle Feed Contaminated with Mycotoxins

Prepared by Nanita Blomquist, Ag-Info Centre, Alberta Agriculture and Rural Development

For more information about the content of this document, contact Barry Yaremcio.
This document is maintained by Kathy Andersen.
This information published to the web on November 28, 2003.
Last Reviewed/Revised on April 24, 2008.