Sometimes you have to bale hay when it contains a little more moisture than you'd prefer - because of high humidity or frequent rains. That's been a problem in Iowa this year with the first cutting. That hay could mold, spoil or suffer heat damage. Brian Lang, Iowa State University Extension crop specialist at Decorah in northeast Iowa, offers the following considerations and information about how to handle hay that's a little wetter than you'd like.
Heat damage causes hay, and especially the protein component, to be less digestible. Hay that is damaged by heating 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 comes from two sources. Some heat is produced by biochemical reactions as the hay cures. This heating is relatively minor and rarely causes hay temperatures to rise above 110-degrees F. At this temperature, hay suffers little damage.
Don't burn the barn down
Most heat in hay is caused by the metabolic activity of microorganisms. Millions of these microbes are in all hay and they thrive when extra moisture is abundant. As metabolic activity of the microbes increases, the temperature of the hay rises.
Hay with only a little excess moisture will likely get no warmer than 120-degrees F. Wetter hay can quickly get as warm as 150-degrees F. Hay that gets this warm nearly always becomes discolored and nutritional value can be very low. If hay temperature rises above 170-degrees 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," he notes. "Be wary of the fire danger with wet hay and be sure to store it away from buildings and other hay just in case of spontaneous combustion."
Guidelines for the use of preservatives
Can the use of hay preservatives help avoid problems with wet hay? Hay can be baled a bit wetter if a preservative like propionic acid is applied as the hay is baled. To get good results from the use of preservatives, it helps to know how the preservative works and what it can and cannot 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, the hay 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 you 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.