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Don’t Burn Down the Barn or Make Your Stock Sick – What to Do With Wet/Moldy Hay

In many parts of the country, this year’s weather was not particularly friendly for putting up hay. With lots of rain throughout the summer, you may have hay that is wetter than usual and that means  an increased risk of fires from spontaneous hay bale combustion.

In this 5:19 video, Simon Whistler explains why wet hay catches on fire. It’s a result of bacteria/microbes in the hay, breaking down plant glucose, and releasing energy, or heat, in the process. Above 15% moisture, the bacteria thrive, doubling their population every ten minutes. This means that as they eat more and more, and the population continues to expand, the amount of heat generated can increase quickly.

How do you know if your hay is heating up?

As Whistler notes, one of the first warnings can be signs of evaporation – like steam rising from the bales, or condensation in the barn. Another is that acrid, tobacco-like odor you’ve smelled that is associated with moldy hay.

Of course, taking your bale’s temperature is one of the best ways to know what’s going on. You can use a long-stem compost thermometer, or drive a metal pipe into the bale and lower a non-mercury thermometer inside, as some experts suggest. But you might find Whistler’s method easiest. He suggests inserting an iron bar into the middle of the stack.

how to take a haystack's temperature

When you pull the bar out two hours later, how it feels in your hand will tell you what is happening in the stack. If you have difficulty holding it, the temperature is 130ºF (54ºC) and you need to take action – moving the bales out of the barn or spreading them apart to allow them to cool down. If the bar is too hot to hold, the stack has reached 150ºF (65ºC) and spontaneous combustion is imminent. Call the fire department first and then move animals and valuables away from the stack. You can move bales and spread them apart from each other to reduce heat, but this can be dangerous as well. As you move the bales, more oxygen may get to bales that are starting to burn, increasing the fire. Whistler describes how firefighters fought fires in Colorado and California with differing techniques and different end results.

Can You Feed Moldy Hay?

Mold is another risk for wet bales. Mold uses the protein and energy in plant tissues to grow, reducing the value of the hay as livestock feed. “Mold also has the potential to produce mycotoxins which in high enough levels could be deadly to animals that ingest it in the extreme circumstance,” write Ben Beckman and Hannah Greenwell, extension educators with University of Lincoln-Nebraska. They add that, though, that the most common problem encountered with moldy hay is that it decreases the amount an animal eats and also decreases ruminal function and overall performance. The combination of low-quality feed and a cold-wet winter can reduce breed back and calf weights can suffer as well.

If you do have moldy hay, and you plan to feed it, here are some things you should do. First, have your hay tested. This will tell you how much you need to feed to meet animal needs. You’ll need to test through the season as the mold and moisture will continue to reduce the value of the hay. Beckman and Greenwell recommend sampling by lot (hay harvested from the same field with a 48 hour period) a few weeks before you plan to feed it.  Then, as you feed, spread the moldy hay out and let your animals pick through it. Provide a source of good, clean hay as well so animals aren’t forced to eat especially moldy chunks.

Precautions When Feeding Moldy Hay

Try not to feed moldy hay to pregnant animals because the mycotoxins can cause fetal abortions. Horses are also very sensitive to moldy hay. To avoid respiratory and toxin issues, keep moldy hay away from horses. And while you’re at it, protect yourself from breathing in dust and mold as you’re feeding. Wear a dust mask to prevent coughing and other respiratory problems.

We hope this information keeps you and your haystack safe and worry free!

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Kathy Voth
Kathy Voth
I am the founder, editor and publisher of On Pasture, now retired. My career spanned 40 years of finding creative solutions to problems, and sharing ideas with people that encouraged them to work together and try new things. From figuring out how to teach livestock to eat weeds, to teaching range management to high schoolers, outdoor ed graduation camping trips with fifty 6th graders at a time, building firebreaks with a 130-goat herd, developing the signs and interpretation for the Storm King Fourteen Memorial trail, receiving the Conservation Service Award for my work building the 150-mile mountain bike trail from Grand Junction, Colorado to Moab, Utah...well, the list is long so I'll stop with, I've had a great time and I'm very grateful.


    • Unfortunately, I have experience with this. Yes, they will eat some of it, but goats aren’t garbage disposals. Remember the cautions included in this article about the potential for mycotoxins to cause problems. And there will be some impact to lungs. They will cough and show discomfort. As the folks from UNL suggest, spread it out, and let them pick and choose and don’t force the issue. And be sure to protect your own lungs as well. Then provide them with an alternative, better hay too.

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