As we drove through the Midwest one summer day and saw field after field of round bales lying in the sunshine, my Irish guest quipped: “Your farmers must be very rich to be able to leave all those big hay bales out in the field.”

He was being facetious, but he had a point. Storage losses can exceed 50% in round bales left uncovered and resting on bare ground.

“To put [round bale] storage losses in perspective, let’s assume you store your hay outside and have a fairly reasonable storage loss of 10%,” says Craig Saxe, an Extension ag agent based in Juneau County, Wis.

“That may not sound all that bad, but a 10% storage loss means that for every 10 bales of hay you harvest, you really only have the equivalent of nine bales of hay to feed,” he says.

Dry matter losses occur based on hay moisture, temperature and the time hay is exposed to these conditions.

“If dry matter loss was the only factor to consider, hay storage under a roof would be an easy top choice,” Saxe says. But due to building costs, especially if you have to build a new facility to store hay, storage under roof can be as expensive as storing hay uncovered on the ground on an annual cost per ton basis.

Brian Holmes, a University of Wisconsin Extension ag engineer, has developed a spreadsheet to analyze the annual cost of various storage methods. You can find his analysis at

Holmes found, of all the methods, the lowest cost alternative was to store round bales on a crushed rock base covered by a tarp. Regardless, Saxe says farmers need to base cost analysis assessments on their own circumstances.

“Consider using your own set of assumptions to determine a storage system that’s right for you,”  Saxe says.