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Value of Covering Silage

Covering a silage pile or pit with plastic requires a lot of manpower and supplies. It is an expense that some producers do not want to incur. Covering with straw, liquid molasses, or leaving the silage uncovered is considered by some to be an alternative to plastic. Not covering a silage pile or pit with plastic has many consequences.

For forages to ensile properly; an anerobic environment is required. Bacteria and other microbes that ferment the material first produce acetic acid, then lactic acid which lowers the pH and stabilizes the silage so it does not deteriorate. If fermentation is complete, there should be minimal amounts of butyric acid present.

During the ensiling process, soluble sugars and proteins are used by the bacteria as a food supply which causes a weight loss or shrink. The longer it takes the plant material to ferment, the greater the weight loss.

Poor fermentation reduces silage quality in many ways:

  1. It takes longer for silage to ferment when oxygen is present. Dry matter losses can be much higher than the 5 to 8% commonly found in silage covered with plastic. Some estimate the losses to be double. A Penn State fact sheet indicates a 75% dry matter loss in the top 10 inches of packed silage when not sealed under plastic.

  2. Spoilage occurs on the top of the silage. The black material is rotted silage. Four inches of freshly packed silage deteriorates into one inch of this material. Dry matter losses are higher than what is perceived by the eye.

  3. Including 5% of the rotted material in the ration reduces total digestibility of the ration by 10%. This material should be removed from the top of the pile or pit prior to feeding.

  4. Silage temperatures increase rapidly during fermentation. If temperatures exceed 40 degrees Celsius, some of the protein is tied to the fibre components and isn’t available to the animal. Depending on length of heating, 10 to 30% of the total protein in the silage may be unavailable.

The impact of aerobic fermentation with uncovered silage reduces the amount of energy and protein available to the animals. The loss of soluble sugars during fermentation reduces TDN or energy content. Additional supplementation may be required to meet animal requirements. Test the silage and balance the rations accordingly.

There’s nothing a producer can do with last year’s silage other than carefuly manage feeding it to the herd. However, covering silage pits and piles with plastic next crop year can increase the amount of feed available for next winter’s feeding plan.

For more information about covering silage pits or piles and the impact on feed value, contact Barry at 403-741-6032 or


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