The faster silage is fed off the face of a bunker or pile, the less time it’s exposed to oxygen and subject to spoilage, says Brian Holmes, a University of Wisconsin ag engineer. He generally suggests a storage design that allows for a 1’/day feedout rate.

“What a lot of people don’t understand is that oxygen can penetrate quite a ways into a feedout face and there have been some measurements made where they’ve actually found the hot zone as far back as 3’,” he says.

Producers may not know that this zone of heating is causing dry-matter losses because it’s out of their sight range, Holmes adds. “The feedout face might actually be cool to the touch – at the face, the readily available carbohydrates have been decomposed days in advance and it has had a chance to cool down.”

Some feeders do realize the losses are occurring, but come up with the wrong solutions, Holmes adds. “You’ll see where people are tunneling down through their silage (see photo above). They have come to realize that a small distance fed out each day results in always feeding spoiled feed. So they will increase their feedout rate by tunneling down through the silage.”

Slow feedout rates or tunneling to avoid the problem suggests that the storage was made too wide in the first place, he says. “They’re feeding out at a much higher rate because they get better feed quality while they are feeding. In the meantime, everything else that’s exposed is deteriorating in much the same way as an uncovered storage.”

His solution is to feed at a faster rate across the face of the forage. “Let’s say the zone of heating is in the 2-3’ range. If you feed out at the rate of 1’/day, the heating can only happen for up to three days before you actually get to that point and feed it out. If you’re feeding at 6” a day, you have up to six days for the decomposition to occur.”

The best solution is to design bunkers and piles for a 1’ feedout rate. That may mean adding bunker walls or building more and smaller piles. Reducing the size of the pile or bunker face ensures fast enough feedout and that the remaining silage stays under plastic and protected from air, Holmes says.

For bunker and pile-sizing assistance, use the spreadsheets available under the heading Silage Storage Type, Sizing and Management on the UW Extension Team Forage – Harvest and Storage Web site.