Frequent spring rains have allowed cool-season forages to grow in abundance. Even when the fields and meadows are 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 cattlemen 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° 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° F; whereas wetter hay can quickly exceed 150°. If the hay rises above 170°, chemical reactions can begin to occur that produce enough heat to quickly raise the temperature above 400° 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, which is adapted from “Preventing hay fires” Martinson, University of Minnesota.

Moisture ranges (%)Comments
Less than 10Too dry. Hay may be brittle and dusty.
10-15Recommended moisture range. Minimal risk of fire.
16-20Could mold. Slight risk of fire hazard.
21-25Will likely mold. Moderate risk of fire hazard.
Greater than 25Severe heat damage likely. High risk of fire hazard.

Source: Cow-Calf Corner newsletter article by Glenn Selk, Oklahoma State University.