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Preserving the value of dry stored hay

Quick facts

  • Bale hay at 15 to 20 percent moisture (wet basis).

  • If stored uncovered, use bales harvested early in the season first, and try to sell or feed all bales before the following spring.

  • If stored outside, place bales on a well-drained surface, such as gravel, old tires or pallets rather than directly on the ground.

  • Consider investing in tarps or storage buildings.

The way you store hay after baling can have a big effect on hay quantity and quality losses, so it’s worth investing additional resources – money, labor and equipment – in hay storage.

This preserves the value of the hay and ensures a good return on your initial investment to bale the hay. Baling uses a large number of resources, including land, labor, seed, fuel, fertilizer and equipment.

Here are some best practices for preserving the value of your baled hay.

Factors affecting losses

Temperature and moisture

Most dry matter and quality losses that occur during storage are due to molds and bacteria that consume hay’s nutrients. These microorganisms generate heat that causes chemical reactions and additional nutrient loss.

In extreme cases, the heat generated by molds and bacteria can cause fires, destroying the hay and the surrounding structures. Molds and bacteria grow and reproduce faster if hay is warm and moist. The more time they have to work, the more damage they can do.

In general, microorganism-caused losses are lower at lower temperatures and moisture levels and shorter storage periods. Because most hay is stored outdoors or in structures that aren’t heated or cooled, storage temperature follows outdoor temperature and is beyond your control.

We have little control over hay storage temperature, plus livestock feeders and hay processors usually need to store hay for year-round use. This means controlling moisture is probably your best strategy for limiting storage losses.


Hay harvested late in the season and consumed during the winter is stored for a relatively short time at relatively low temperatures and should have minimal losses. Hay harvested early in the season and stored into winter will be subject to some warm temperatures before winter arrives and is likely to have greater losses.

Expect the greatest losses with hay that’s stored through winter and into the following spring and summer. According to research by Oklahoma State University, losses after 12 to 18 months of storage are twice as great as losses after nine months of storage.

Recommended moisture content for baling

The timing of baling is critical to maximizing the hay’s value. Optimum moisture for baling is between 15 to 20 percent moisture (wet basis), which is low enough to prevent mold activity.

Baling at lower than 15 percent moisture will result in greater harvesting losses, especially for alfalfa, because leaf loss increases as moisture decreases.

Large hay packages, especially large rectangular bales, don’t lose much moisture after baling. This is why it’s important to bale at the proper moisture, instead of baling at higher moisture and counting on some natural drying in storage.

Baling at higher moisture

If you must bale at higher moisture, here are some options:

  • Bale at slightly higher moisture (20 to 30 percent) and apply a preservative that inhibits mold growth in storage.
  • Bale at higher moisture (20 to 35 percent) and artificially dry the bales.
  • Bale at much higher moisture (50 to 65 percent) and ensile the bales by storing them sealed in plastic.

Recommended moisture content for storage

After baling, hay should continue to be at moisture content below 20 percent for storage. Storing hay at moisture contents above 20 percent will result in:

  • Some molding and heating.

  • Dry matter and nutrient loss.

  • Some discoloration.

Impact of storage moisture

A study of small rectangular bales stored in a barn at the U.S. Dairy Forage Research Center in Madison, Wis. showed that dry matter loss increased with storage moisture. Quality loss was also greater in the wetter bales.

Dry matter and quality loss

Storage moisture Dry matter loss Digestible dry matter loss Crude protein loss
11 to 20% 4.50% 6.20% 6.00%
20 to 25% 7.90% 11.80% 8.80%
25 to 34% 10.90% 13.50% 7.50%

Protecting bales in storage

If you store dry hay outside, find ways to prevent direct contact between the ground and the bales’ bottom layer. Bales resting on the ground will absorb enough moisture to grow mold.

Research studies and farmer experience show that placing hay bales on layers of coarse gravel, old tires or wood pallets is an effective way to prevent soil moisture from wetting the hay. Studies in other states indicate storage losses are about 5 percent less for hay stored on gravel, tires or pallets compared to hay stored directly on the ground.

Research: Hay storage in Minnesota

To better understand expected losses, the University of Minnesota West Central Research and Outreach Center in Morris studied different hay storage methods in Minnesota conditions.


Round bales vs. rectangular bales

There is no clear advantage for one bale type over the other.

Despite the tendency for uncovered large rectangular bales to absorb more moisture than large round bales, our Morris study indicated no significant difference in average dry matter loss for the two bale types over an eight-month storage period.


Bill Wilcke, retired Extension engineer; Greg Cuomo, CFANS associate dean for research and graduate programs; Krishona Martinson, Extension equine specialist; and Cheryl Fox

Reviewed in 2018

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