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Preserving the value of dry stored hay

What you need to know

  • 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 amount of resources, including land, labor, seed, fuel, fertilizer and equipment.

On this webpage, you’ll find hay storage research findings and best practices for preserving the value of your baled hay.

A tractor collecting hay

Factors affecting losses


Baling: Recommended moisture content

Timing of baling is critical to maximize 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 a higher moisture and counting on some natural drying in storage.

Baling at higher moistures

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

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

Storage: Recommended moisture content

After baling, hay should continue to be at moisture contents 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.

Study: 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 (Table 1). Quality loss was also greater in the wetter bales.

Table 1: 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

Square bales stacked up

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 rewetting the hay via soil moisture. 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

Studies don’t show a clear advantage for one bale type over the other.

For example, 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, emeritus Extension engineer; Greg Cuomo, Associate Dean, Rosemount Research and Outreach Center, Cheryl Fox and Krishona Martinson, Extension equine specialist

Reviewed in 2018

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