The moisture content of your hay is important to keep in mind because hay baled with high moisture content levels can have negative impacts such as hay spoilage, barn fires, and decreased nutritive values.
A natural event, commonly referred to as “heating,” occurs when growing forages are cut and continue to give off heat due to respiration. Plant and mold respiration generates lots of heat; this does little but provide proper growing conditions for bacteria. If wet hay is baled while it is too wet, microbe populations will flourish and intensify the heating process. This results in hay that is lower in nutritive value and dry matter availability.
Allowing cut hay to dry (or cure) will slow down the respiration process. Respiration slows down as moisture content decreases but will not completely stop until plant moisture reaches 20 percent or less. Moisture levels above 20 percent allow the respiration process to continue and mold to develop, this then produces heat.
Moisture levels for safe storage vary with the size and density of the bale and the type of hay. Hay in small square bales should be baled between 15 and 22 percent moisture to minimize leaf shattering, molding and heating. Larger round bales or the large square bales are larger in size and weight. So obviously these will retain core moisture, thus internal heat longer than the small square bales. These larger bales should not be baled with a moisture content level in excess of 18 percent. If you are deciding to bale your large bales while the moisture content is in excess of 22 percent, you should not stack the bales for at least 30 days and consider this when feeding.
If the internal temperature of a bale of hay exceeds 130 degrees F, a chemical reaction occurs within the bales that releases flammable gases that can ignite. So when harvesting, the most effective way to reduce the potential of spontaneous combustion in hay bales is to make sure the cut has dried sufficiently prior to baling. Hay that has been rained on or is slightly wet should be mechanically teddered, or fluffed, to speed up the drying process.
Check newly stacked hay for possible heating, especially for hay that has been rained on. It is not unusual for hay to heat to 100 degrees F within the first couple of weeks after it is baled.
Details from this article are from the Texas Cooperative Extension Publication “The Burning Bale,” by David W. Smith; The Samuel Roberts Noble Foundation publication, “Nutritive Value of Hay is Critical at Baling and Feeding,” www.noble.org; and the U.S. Drought Monitor, http://drought.unl.edu/dm/monitor.html. For more information, please contact Chelsea Dorward at the Texas A&M AgriLife Extension Service – Bosque County Office at 254-435-2331 or firstname.lastname@example.org