Forage is too valuable to be lost because bunker silos or silage piles are sized incorrectly or inadequately managed, says Brian Holmes, a University of Wisconsin-Extension ag engineer.

He explains that each 10% loss of dry matter for hay silage represents about $1,940 a year per 100 cows when they’re fed a 50-50 ration of hay and corn silage. Dry matter loss occurs in silos because of inadequate feed-out rates, inadequate silage density, exposure to oxygen or rainwater, and juice seepage.

Holmes says these losses can be avoided or minimized.

For example, adding a 100’-long wall to create three bunker silos instead of two will add an initial cost of $7,500 when the wall costs $75/foot. Using a 12% depreciation, interest, repairs, taxes and insurance factor, the $7,500 initial cost is converted to an annual cost of $900. The result is a net profit of $1,040 for a 100-cow herd.

You can minimize seepage by harvesting at a moisture content below 70% and covering the forage to protect it from rain.

You can control density with the packing process, forage moisture content, packing tractor weight, delivery rate of forage from the field, and depth of forage. High rates of delivery from high-capacity self-propelled forage harvesters can result in low-density silage, which allows easy oxygen penetration into the exposed surfaces.

Eight-mil plastic held close to the silage surface by a weighting material limits oxygen and rainfall exposure. Some producers report improved forage quality along bunker walls when they line the walls with plastic film and place the wall lining plastic under the top cover plastic at the joint. The wall plastic prevents water running down the wall from getting into the silage. The wall plastic also keeps oxygen from penetrating through wall cracks into the silage.

The rate of feed-out (inches per day removed from the face) is influenced by how much feed is needed each day and the area of the feed-out face. A common mistake is to design a horizontal silo so wide that the feed-out rate is too low. Wide bunker silos are less expensive than narrow silos because narrow silos require more length of bunker wall for a given volume stored. Producers can cut costs by making bunker silos wide, but that can have a high annual cost due to higher dry matter loss, says Holmes.