Nutrition
Understanding
Wet Hay
By Glenn Selk, Oklahoma State University
Emeritus Extension Animal Scientist
Frequent spring rains around the country have
allowed cool season forages to grow in abundance.
Even when the fields and meadows dry enough to
cut standing forages, harvesting and baling cool
season crops such as fescue and wheat hay can
be a challenge during a wet spring. The timing
of the rains can make it difficult for producers
that are trying hard to put quality hay in the
bale for next winter’s feed supply. All producers
that harvest hay occasionally will put up hay
that “gets wet” from time to time. Therefore,
ranchers and hay farmers need to understand the
impact of “wet hay” in the tightly wound bales.
Extra moisture in hay can cause heat inside the
hay bale or hay stack. Heat produced by the
bale comes from two sources: First) biochemical
reactions from plants themselves as hay cures.
(This heating is minor and rarely causes the hay
temperature to exceed 110 degrees F. Very little
if any damage occurs if the hay never exceeds
110 F.); Second) Most heat in hay is caused by
the metabolic activity of microorganisms. They
exist in all hay and thrive when extra moisture is
abundant. When the activity of these microbes
increases, hay temperature rises. Hay with a little
extra moisture may not exceed 120 degrees
F., whereas, wetter hay can quickly exceed 150
degrees. If the hay rises above 170 degrees,
chemical reactions can begin to occur that produce
enough heat to quickly raise the temperature
above 400 degrees and the wet hay can begin to
burn and cause fires. Be wary of the fire danger
of wet hay and store it away from buildings and
other “good” hay just in case this would occur.
Below is a table with moisture guidelines at
time of baling. (Adapted from “Preventing hay
fires” Martinson, University of Minnesota)
Moisture ranges (%) Comments
Less than 10 Too dry. Hay may be brittle and dusty
10 - 15 Recommended moisture range. Minimal risk of fire
16 - 20 Could mold. Slight risk of fire hazard
21 -25 Will likely mold. Moderate risk of fire hazard
Greater than 25 Severe heat damage likely. High risk of fire hazard
114 | JUNE/JULY 2019