UNL CropWatch June 23, 2010: Be Prepared for Potential Heat Damage To Moist Hay
June 23, 2010
Did you bale some first cutting hay a little tough due to high humidity and frequent rain showers? If so, your hay could mold, spoil, or suffer heat damage.
Excessive heat can cause hay, and especially the protein, to be less digestible. Heat-damaged hay often turns brownish and has a sweet caramel odor. Cattle often eat this hay readily, but because of the heat damage, its nutritional value may be low.
Heat produced by a bale basically comes from two sources.
Some heat is produced by biochemical reactions from the plants as the hay cures.
This heating is relatively minor and rarely causes hay temperature to rise above 110ºF. Little damage occurs to hay that does not reach 110ºF.
Most heat in hay, though, is caused by the metabolic activity of microorganisms. Millions of these microbes exist in all hay, but they thrive when moisture is abundant.
As the metabolic activity of these microbes increases, the temperature of the hay increases. Hay with only a little excess moisture probably won’t get warmer than 120ºF. Wetter hay, though, can quickly get as warm as 150ºF. Hay that gets this warm nearly always becomes discolored, and nutritional value can be very low.
If hay temperatures rise above 170ºF, chemical reactions can produce enough heat to quickly raise temperatures to over 400ºF and cause a fire. Be alert to this potential fire hazard and store wet hay away from buildings and other hay.
Also, before feeding wet hay, be sure to get a thorough forage test to determine its nutritional value.
Bruce Anderson
Extension Forage Specialist
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