University of Tennessee animal scientists conducted a trial to compare different methods of storing large round bales of grass hay. The hay was cut and baled in June in Moore County, Tennessee. The bales were weighed at the time of harvest and storage. Then they were weighed again the following January at the time of winter feeding. The following table lists the type of storage and the resulting percentage hay loss.

Table 1. Losses of Hay Stored using Six Methods of Storage

Type of Storage 
Percentage (%) Hay Loss
On ground, no cover 
On tires, no cover
On ground, covered
On tires, covered
Net wrap on ground
In barn

Obviously, it would be ideal to store the hay inside, but that will not often be practical. The next best option is when the hay is stored on something that gets the hay off of the ground under a rain shedding cover. Different areas of the country may have different results due to variation in rain and snow fall. (Source: Dr. Clyde Lane, University of Tennessee Department of Animal Science).

Source: Glenn Selk, Oklahoma State University Extension Cattle Reproduction
Specialist and Clyde Lane, Beef Specialist, University of Tennessee