University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources

How Preservatives Can Help

When baling hay, moisture content can influence yield, quality and storability. If the hay is too dry, leaves will fall off, reducing both quality and yield, but if it’s too wet, it can get moldy or overheat and catch fire. There is a narrow moisture range that results in good hay that keeps well.

Hay can be baled a bit wetter if a preservative like propionic acid is applied as it’s baled. To get good results from preservatives, though, it helps to know how it works and what it can and can not do.

Baled hay naturally contains millions of bacteria and mold fungi. As they consume hay nutrients, these microbes produce heat. The duration and intensity of this heat determines the amount of damage. This heat also forces moisture out of the bale, something called “going through a sweat.” Usually, hay gets dry enough that the microbes die or go dormant, but when there’s too much moisture, it can mold or overheat.

Preservatives will kill many of the microbes so less heat is produced, giving hay time to dry naturally, without the “sweat.” As it dries, the preservative also vaporizes and disappears. If we stack bales tightly into storage soon after baling or fail to allow for natural drying, the remaining microbes eventually will produce mold and heat. Also, if rain, high humidity, or other sources moisten the hay later, microbial activity can redevelop since the protection from preservatives lasts only a short time.

Preservatives can help make good hay at higher moisture levels, but correct management is needed to keep that hay in good condition.

Bruce Anderson
Extension Forage Specialist

May 25, 2007

Exercise Caution When Baling Wet Hay

Do you sometimes bale hay a little tough due to high humidity or frequent rains? If so, your hay could mold, spoil or suffer heat damage.

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

Heat produced by a bale basically comes from two sources. Some heat is produced by biochemical reactions from the plants as hay cures. This heating is relatively minor and rarely causes hay temperature to rise above 110° F. At this temperature, the hay suffers little damage.

Most heat in hay, though, is caused by the metabolic activity of microorganisms. Millions of these microbes exist in all hay and they thrive when extra moisture is abundant.

As the metabolic activity of these microbes increases, the temperature of the hay rises. Hay with only a little excess moisture probably will get no warmer than 120°.F Wetter hay, though, quickly can get as warm as 150°.F Hay that gets this warm nearly always becomes discolored, and nutritional value can be very low. If hay temperature rises above 170 °.F, chemical reactions can produce enough heat to quickly raise temperatures over 400 degrees and cause fires.

We all bale hay a little too wet from time to time. Be wary of the fire danger with wet hay and store it away from buildings and other hay just in case.

Also, know that the feed value of wet hay is less than optimum. Get a thorough forage test and use this hay accordingly.

Bruce Anderson
Extension Forage Specialist

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© 2007 by the University of Nebraska Board of Regents. All rights reserved.
Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.
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