Producers can lose up to about $17/ton to heat damage in their hay and haylage and should take more steps to keep forage cool, a prominent forage agronomist says.

Heating burns off essential nutrients, such as sugars and crude protein, and that lowers quality, reduces dry matter and costs producers money, says Dan Undersander, University of Wisconsin Extension forage specialist. In a 2012 Wisconsin study, 3,600 farmer-submitted hay and haylage samples tested at Midwestern forage labs showed an average total digestible nutrient loss of $10/ton.

“Whenever you feel a hot hay bale, think, ‘I’m losing energy,’ ” says Undersander. “We really ought to pay more attention and try to minimize that.”

As hay cures in the field, it heats, and plant and microbial respiration turns sugars to water and carbon dioxide. Heating slows as hay dries, but doesn’t stop until hay is at less than 20% moisture.

Hot hay, at moistures between 20% and 35%, can be a breeding ground for molds, which do more than use up valuable energy. Molds can produce mycotoxins, which cause respiratory diseases, allergic reactions and abortions. Molds are also a problem in poorly packed haylage, Undersander says.

Too much heat also brings the risk of fire. If hay reaches temperatures above 160º F, it can spontaneously combust, says Dave Hill, program director at Penn State University’s Managing Agricultural Emergencies program.

Hay can be baled at higher moisture levels with cooler air temperatures if bales are smaller or allowed to sweat a bit before being stacked.

Haylage, on the other hand, can be stored too dry. It generates heat through the fermentation process, and the combination of heat, air and haylage can cause it to internally combust, Hill says.

To reduce heat damage, growers should:

• Bale hay at less than 25% moisture. Wide swaths that cover 70% of the cut area will dry hay quickly in the field.

• Bale large round and medium to large square bales at lower moisture levels than when baling smaller bales. That’s especially important if using newer balers that make tighter bales. In the less-humid West, producers can dry hay to around 14% moisture before baling large squares. That allows them to make 1-ton bales, Undersander says. Where humidity is higher, producers are limited to lighter-weight bales.

• Use hay preservatives at baling if hay is at 18% moisture or higher. Undersander recommends propionic acid because it is also naturally produced in cows’ rumens for energy absorption.

• Let bales above 14% moisture sweat by leaving space between them and allowing cool air to circulate. Put enough space between them to limit potential damage if bales go up in flames.

• Pack haylage in wrapped bales, tubes or bunkers well to keep oxygen out and fungal growth to a minimum. Undersander recommends packing to a density of 45 lbs per cubic foot. That leaves porosity, the amount of airspace between particles, at about 40%. “We don’t want more than that.”

• Manage feedout to prevent oxygen from spurring heating in haylage. If the forage is packed at a density of 45 lbs per cubic foot, oxygen should diffuse about 30” into exposed haylage. Remove 12” of feed per day off the face of the pile or bunker to keep the oxygen from doing much damage.

“That way, two and a half days is the longest time (haylage) would be exposed to oxygen before you’re feeding it,” Undersander says.

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