is it safe to feed moist hay to horses
Q.I was recently surprised to learn that my barn already has some first-cutting hay, and they’ve started to feed it. It’s very green and feels slightly damp to me. Is it safe to feed hay off the field? Does it need to be stored for some period of time before it should be fed?

—Via e-mail

A.First of all, I’m amazed that we are barely in March and you already have a cutting of hay. Don’t tell those still buried under feet of snow and inches of rain!

You are right to be cautious if the hay feels damp. This could indicate it might still go through a fermentation process, during which time it should not be fed. Growing up in England where the conditions were often damp, it was generally understood that the current year’s hay put up in late spring should not be fed until the autumn. In hindsight this was based on anecdotal wisdom, but there was some truth to it due to the fermentation issue. However, the waiting period between cutting and feeding might only need to be a few weeks.

Hay Moisture Content, Fermentation, and Other Risks

Hay put up with 12% or less moisture isn’t going to go through much fermentation, if any, and is safe to feed right after harvest. Hay that does ferment will lose some nutritional value and could become moldy and dusty. The level of nutrient loss, mold, and dust will depend on the moisture level.

Beyond the lowered nutritional value there’s also a danger when storing damp hay because fermentation might cause the bales to self-combust. Every year, hay with higher moisture contents causes barn fires. Think carefully about where hay is stored. I was once in a barn where the hay was kept at ground level with an apartment above. The owners never chose to buy hay off the field as they did not want to risk the possibility of a fire under someone’s home! Many barns keep their hay in the barn with the horses, so the fire risk is a consideration here as well.

Personally, I’m not a fan of keeping hay in the barn with the horses because if ignited, no matter the cause, a hay fire is extremely hard to put out. Try to force your hand in to the center of one of the new bales of hay and make sure that it’s not warm to the touch which would indicate active fermentation.

Is My Hay Safe?

The easiest way to tell if the hay is too damp is to test it with a special probe that measures moisture. This might be available from your local university extension office. You could also collect and send a sample to a lab to test the moisture level.

A slightly cruder test is the twist test. This is carried out by taking a handful of hay and twisting it with your hands in a circular motion. If hay is ready to bale, the stems should break and crack.

Changing Hay Sources

When introducing new hay into your horse’s diet, do so gradually and watch carefully for signs of digestive disturbance. New hay, no matter how moist, should always be introduced slowly because research has shown that changes in hay, even when the type remains the same, can increase a horse’s colic risk for up to three weeks.

Take-Home Message

It is not uncommon for early hay cuttings to get rained on, and this isn’t necessarily a bad thing as long as the hay is given adequate opportunity to dry properly before baling. In fact, because most horse owners don’t like hay that’s been rained on, you can often purchase such hay at a decent price.

While buying hay off the field is often cheaper than buying barn-stored hay, there are some potential disadvantages, too. You must be observant and do your due diligence to mitigate risk. You need to be sure that the hay has finished the fermentation process before it is fed. And that can take a varying amount of time depending on the moisture content when baled, relative humidity, and other factors.