The difference between winners and losers among those who bag silage usually boils down to a single concept: Management.
Do things right and the quality of feed coming out of bags can match — even exceed — that of silage stored in tower or bunker structures. Slip up in one or two key areas, though, and problems likely await.
For custom baggers, that means disappointed clients.
Striving for high density at filling is the surest way to make high-quality bagged silage. Harvesting at the right maturity and moisture gives you a leg up, says Richard Muck, U.S. Dairy Forage Research Center ag engineer in Madison, WI.
“It's similar to a bunker silo in that you typically want material in that 60-70% moisture range,” he says. “If you get too much drier than that, the material becomes more porous. That lets more air in and sets the stage for spoilage.”
Muck's 2000 study of bagging operations, conducted at three University of Wisconsin Ag Experiment Stations, bears out the point. He looked at dry matter losses (both gaseous loss and spoilage) for a variety of corn and alfalfa silages put up by different operators using several types of machines.
Of the 15 bags studied, Muck found losses ranging as high as 38%, with an average loss of 14%. When he took out three bags with the most severe losses — 16-25% spoilage — average spoilage loss dropped to less than 2% and total losses to less than 10%. Those kinds of numbers are similar to losses commonly reported in tower silos.
While the highest losses could be attributed to other factors, “spoilage losses were primarily associated with drier, porous silages,” says Muck.
The skill levels of bagging machine operators are important, too.
“There's an art to running a bagger,” says Bill Kautz, a technical services director at Chr. Hansen Biosystems, Milwaukee, WI. “It's not a matter of just climbing onto the machine and going at it. It takes practice.”
Here are tips for good machine operation:
Match equipment to bagging machine. “Twenty years ago, a 45-hp tractor was all you needed to run a bagger. Today, 70 to 80 hp is a minimum,” notes Greg Tollefson, a Pigeon Falls, WI, dairyman who rents out baggers. “If the tractor is underpowered, adjust the pressure on the bagging machine. That makes filling and packing trickier.”
Also, match bag size to chopping and unloading equipment. If you only harvest 10 loads a day, you may not fill fast enough to justify using 9'- or 10'-diameter bags.
Monitor unloading. “The basic idea is to keep pushing material into the machine at a steady rate so that the machine works at full capacity. That's what it was designed to do,” says Mark Lankey, of Tri-County Seeds and Chemicals/Custom Bagging Services, Wonewoc, WI. He suggests unloading feed from the forage box into the center of the machine.
“The rotors on these machines are designed to spread feed out evenly as it enters the bag,” explains Lankey. “If all the feed goes to one side of the bagging machine, it's tougher to get a smooth pack.”
Avoid overfilling. “One of the most common mistakes we see is people trying to push too much feed into the bag as they start filling,” says Lankey. “They might gain a little on the diameter, but they end up losing on total length. It also stretches the sidewalls and weakens the structure of the bag.”
Overfilling can also cause feed to shift around and separate within a bag, hampering fermentation. Sealing bags properly may also be more difficult.
Use inoculants — they help preserve good-quality feed, says Lankey, who sells inoculant products. For bagged silage systems, he recommends products without mold inhibitors.
For bunker silos, products with mold inhibitors are sometimes recommended, he says. “With bunkers, you're putting silage in layers. That leaves room for air to get in and create molds. A bag is like a fruit jar. You're pushing the air out and then sealing it. Molds aren't as much of a problem.”
A final point: All the work put in at filling can go for naught if bags tear during storage. Storing bags on a hard, well-drained surface helps head off problems and makes feed-out easier.
“You don't necessarily need an asphalt pad, just well-packed crushed material in an area that's free of moisture,” says Joe Harrison, dairy scientist at Washington State University. Harrison also recommends taking steps to keep birds, rodents and other critters away from bags.