By Neil Tietz
Dairy producers who apply propionic acid to not-dry-enough hay when making big square bales are probably saving valuable nutrients, a U.S. Dairy Forage Research Center study suggests.
Alfalfa-orchardgrass hay treated with a commercial buffered propionic acid-based preservative and packaged in 3 x 3 x 6’ bales at up to 27.4% moisture heated less than untreated hay during a 73-day storage period. At the end of the trial, treated hay was higher in quality, and a lamb feeding trial revealed that it was more digestible, says USDA-ARS agronomist and dairy scientist Wayne Coblentz, who headed the study.
Results with 5’-diameter round bales were disappointing, however. Applying the preservative to high-moisture hay going into those bales didn’t consistently reduce heating or improve forage quality, he reports.
“Some other researchers have expressed to me that they’ve had similar responses with round bales,” says Coblentz, who’ll discuss the study in a forage seminar at the Sept. 30-Oct. 4 World Dairy Expo in Madison, WI. His presentation is set for 1:30 p.m., Oct. 1, in the Arena Building at the Alliant Energy Center.
Small square bales can be stored safely without a preservative at moisture levels up to 20%, says Coblentz. They have more surface area per pound of dry matter than big square and round bales, so heat and moisture can escape.
“For a large hay package, when you start getting into the upper teens, there’s probably some likelihood, especially with alfalfa, that you’re going to see some evidence of heating,” he says.
Heating causes excessive dry matter losses, reductions in energy density and protein digestibility – and in extreme cases, fire.
In the study, big square bales were made at 19.6%, 23.8% and 27.4% moisture, and the preservative application rates were 0%, 0.6% and 1% of the wet bale weight. The preservative was applied directly into the baler’s bale chamber. Heating was measured in heating degree days, which is the daily difference between the internal bale temperature and 86° F.
The preservative reduced heating at all bale moisture levels and treatment rates, Coblentz reports. At the 27.4% moisture level, bales treated with the 1% application rate accumulated only 37% as many heating degree days as untreated bales. The 0.6% rate reduced heating in that hay, but not as much as the higher rate.
The two application rates performed similarly in hay baled at 19.6% and 23.8% moisture, and treated bales accumulated far fewer heating degree days than untreated bales.
However, bales in the study were treated and stored individually, and Coblentz cautions that his results may not apply to on-farm situations.
“Square bales normally are picked up immediately and stacked somewhere,” he says. “That’s an entirely different environment than one bale standing alone.”
The researcher isn’t sure why the preservative was ineffective on round bales. In that part of the study, 5 x 5’ alfalfa bales ranging in moisture from 10.2% to 40.4% were treated at a single application rate – 0.5% of the wet bale weight. Temperatures of treated and untreated bales were monitored for as long as heating lasted, which was up to five months.
All bales above 20% moisture heated during the first 28 days of storage. The preservative reduced heating, but not by much. Then, elevated temperatures lasted longer in those bales than in untreated ones. Acid treatment tends to make hay retain moisture longer, regardless of bale type, says Coblentz. In this case, treated bales made at more than 30% moisture eventually accumulated more heating degree days than untreated bales.
The problem may have been partly due to the preservative application method. On a round baler, preservative usually is applied by an aftermarket system mounted above the pickup, and it sprays across the full pickup width. When the windrow is narrower than the pickup, some of the preservative is wasted, and the actual application rate may be too low.
“The other thing is, when you get to a certain bale size, I suspect there’s a possibility that the size of the bale just overwhelms the product,” says Coblentz.
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