Dairies can save valuable feed – and combat air pollution – by minimizing the time silage is exposed to air during feedout, says a University of California-Davis air quality Extension specialist.

Frank Mitloehner has found that silage dry matter losses – typically totaling 20-30% in his state – are mostly in the form of gasses that escape after the bunker or pile is opened. Those gasses, called volatile organic compounds (VOCs), are a “very significant” contributor to total emissions from California dairies, he says.

VOCs contain nutrients beneficial to cows, but quickly evaporate when silage contacts air.

“Every compound that can go into the air will go into the air within approximately 12 hours,” says Mitloehner, who has studied emissions from corn silage and alfalfa haylage piles.

VOC emissions are regulated in central California, where dairies applying for operating permits choose from a list of recommended silage management practices. Mitloehner predicts that the requirements will eventually become more stringent. Meanwhile, he urges producers to take steps to reduce silage losses.

“People are always reluctant to make changes,” he says. “But it makes no sense to look away when you have an issue that makes you lose a significant portion of your feed.”

Many silage piles are built too big, with steep sidewalls that prevent proper packing. During feedout, their faces are so big that a producer can only remove a few inches of silage per day.

“What you really want to do is minimize the size of the face so that he (the producer) goes to a greater depth. But minimizing the size of the face is not just a question of the physical size of the pile. It’s also a question of how you deface.”

Mitloehner recommends the use of defacers because they create smooth faces.

“Whether you use a front-end loader that rips a very uneven face or a defacer makes a big difference with respect to how much face area is exposed to air.”

Loaders also tend to lift the silage, allowing air between layers, he says.

He would like to see several feet of silage removed from each face daily. That can be achieved with multiple small piles or silage bags, if space is available.

“If you could go to 5’ or 6’ a day, which is often the case using bags, then you minimize the total amount of compounds that go into the air,” he says.

However, if that much silage is removed but only fed once a day, dry matter may be lost in the feed lane.

“You really have to think of the whole system – not just the pile, but also how you mix and how you feed,” says Mitloehner.

The other time silage loses dry matter is during the first five days after a bunker is filled or a pile made, he says. Those gaseous losses aren’t VOCs, but carbon dioxide and so-called silo gas, which is emitted in high concentrations and harmful to humans. To minimize the risk to workers covering the silage, he says to do that job right away, before the gas begins to escape.

“It is absolutely paramount to cover that pile as fast as you can get to it,” says Mitloehner. “I don’t mean three or four days later; I mean immediately. If you don’t do that, first of all you will have significant dry matter losses during that time; secondly, you will have a very significant exposure risk to people.”

Silo gas, he adds, “is nothing to joke about. It is a very serious health issue.”