Factors Controlling Silage Quality

Key factors to making excellent-quality silage are forage quality at time of harvest, suitability of forage for ensiling, harvest and preservation techniques and storage methods, says Bob Schultheis, University of Missouri Extension natural resource engineering specialist who's based in Marshfield, Mo.

Controlling these factors involves achieving proper carbohydrate levels, moisture content and oxygen exclusion.

Carbohydrate Level

Carbohydrate levels are directly tied to the stage of maturity at harvest. The ideal crop will have adequate fermentable carbohydrates, low buffering capacity and the physical structure suitable for compacting.

“We're usually looking at a harvest period of several days, so we're controlling carbohydrate level by what crop maturity stage the crop is harvested at,” Schultheis says.

Recommended cutting stage:

  • Corn = one-half to two-thirds milk line
  • Cereal crops = boot to dough
  • Fescue = boot
  • Orchardgrass = when blooms have emerged
  • Clover = one-quarter to one-half bloom
  • Alfalfa = bud to one-tenth bloom

“On most of these crops, the leaves are going to contain about two-thirds of plant nutrients,” he says. “The growth stage that is chosen will really impact the intake and quality of the forage. Remember, preservation can’t enhance the forage quality, so make the most of what you have.”

Moisture Content

Moisture content depends on the type of silo that you’re using.

  • Conventional upright silo = 63% to 68% moisture
  • Oxygen‐limiting upright silo = 55% to 60% moisture
  • Horizontal silo = 65% to 70% moisture
  • Bales = 45% to 60% moisture
  • Bags = 60% to 70% moisture

 “If it's too wet, you’ll get seepage, undesirable clostridial activity, high butyric acid levels and high fermentation losses, which results in animal intake and performance losses,” he says.

However, if you put up silage that's too dry, then it's difficult to eliminate the air that's in it when trying to pack it down. The stored forage will struggle to reach a sufficiently low pH level for fermentation, and aerobic deterioration will be high.

“I’ve seen people try to use a garden hose into a silage blower to add water to too-dry silage to get it wetter,” he says. “To get a 1% moisture content change, it takes about 20 pounds of water for every ton of material that you put in, and a garden hose usually can’t give enough water at a high enough flow rate to achieve the needed moisture.”

Oxygen Exclusion

The three rules of oxygen exclusion are chop the forage short, fill the silo quickly and make sure that you exclude all the air so that the harvested material can ferment properly.  

Oxygen exclusion starts with chopping length, which is usually 3/8" to 1/2" particle length or 3/4" for corn silage.

When filling a horizontal silo, at least three people are needed to fill it properly – one to harvest, one to transport and one to pack the forage. Filling should occur as quickly as possible, and then, cover the silo as soon as filling is complete. All surfaces should be smooth, so water drains off. Two 6-mil sheets of plastic are preferred over a single sheet, and the sheets should overlap by at least 4' to 6' before securing them with tires or other weights. Leaving the silo open or failing to seal it tight will damage the forage and slow down the fermentation process.

For a bunker or trench silo, construct the silo with good drainage, so water can’t run into it and ruin the fermentation process. Slope the floor at least 1/8" per foot toward the center and toward the open ends. Inspect bunker walls for cracks that might create air penetration.

“When packing forage, spread and pack no more than 6" layers at a time because if it is spread as a 1' layer and packed down, you'll pack the top six, but the bottom 6" will still be loose and won’t get proper fermentation, ” Schultheis adds. “Wheel tractors will pack better than track-type tractors because they provide more ground pressure”

For more information on silage-making, excellent resources are available at http://extension.missouri.edu/webster/pres-2015-11-10.aspx.