Bunker silos covered with plastic and tires could be a thing of the past someday. In their place could be an edible covering currently under investigation at the University of Illinois.

Researchers Larry Berger and J. Sewell began exploring the concept of covering bunkers with an edible material a few years ago. Their preliminary work showed an edible covering made of a salt-starch combination did a good job reducing spoilage. "We had a significant reduction in spoilage with our salt-starch covering," says Berger, a beef nutritionist at the University of Illinois.

However, applying the mixture to silage proved to be too labor intensive and time consuming, so they headed back to the lab for a better idea.

The result of their most recent work is a modified formula that effectively protects the silage from spoilage, and a new application technique that is much easier to apply to silage in a bunker.

The new edible covering is still made of a salt-starch combination, but it has a few modifications. For example, the new formula calls for ground wheat instead of flour and tap water instead of boiling water. It also does not contain soybean oil and potassium bitartrate, like in the original recipe. Berger and Sewell also reduced the covering’s moisture level from 50 percent to 30 percent in the new formula.

Although they were interested in the edible covering’s effectiveness at reducing spoilage, the researchers were most interested in finding a practical way to apply it on large bunkers. Their investigation led them to try three tools not typically used to cover a bunker: a concrete pump, an air compressor and a garden sprayer.

They used a commercial concrete pump with a vertical shaft mixer to mix the ingredients. They chose this equipment because it can be powered by a tractor’s hydraulic system, which would make it more practical to apply on-farm. Next, they used a commercial air compressor to spray the mixture on the silage. On top of that they sprayed an edible wax using a small garden sprayer.

The results show the coverings effectively protected the silage and reduced spoilage, Berger says. And when they fed the covering at the rate of 2.5 percent of total diet dry matter to growing beef heifers, the animals didn’t suffer reduced intake, nor did they sort the cover. "The animals consumed it readily," Berger says.

Although more work is needed before this technique can be applied on-farm, the use of an edible covering may be cost-effective. Berger estimates the cost to be 10 to 12 cents per square foot of silage. The other added benefit of an edible covering is that it eliminates the need to dispose of the used plastic.

The study’s results were reported at the joint dairy and animal science meetings held in Phoenix, Ariz., earlier this summer.