Countering Heat Damage To Moist Hay

Countering Heat Damage To Moist Hay

May 29, 2009

Did you bale some first cutting hay a little tough due to high humidity and frequent rain showers? If so, it could mold, spoil, or suffer heat damage.

Excessive heat can cause hay to be less digestible, especially the protein. Heat-damaged hay often turns a brownish color and has a sweet caramel odor. Cattle often eat this hay readily, but because of the heat damage, its nutritional value might be low.

Heat produced by a bale basically comes from two sources.

  • The plants produce some heat through biochemical reactions as hay cures. This heating is relatively minor and rarely causes hay temperature to rise above 110°. Little damage occurs to hay cooler than 110°.


  • Most heat in hay is caused by the metabolic activity of microorganisms. Millions of these microbes exist in all hay, but they will thrive and cause even more heat when extra moisture is abundant. As the metabolic activity of these microbes increases, the temperature of your hay rises. Hay with only a little excess moisture probably will get no warmer than 120°. Wetter hay, though, quickly can get as warm as 150°. Hay that gets this warm nearly always becomes discolored and its nutritional value will drop. If hay temperatures rise above 170°, chemical reactions can quickly raise temperatures to over 400° and start a fire.

We all bale hay a little too wet from time to time, but be wary of the fire danger that can result from this practice. Store baled moist hay away from buildings and other hay. Also, remember that it likely will have a lower feed value and be sure to get a thorough forage test and feed accordingly.

Bruce Anderson
Extension Forage Specialist



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