Research has shown that storage losses in large round bales stored outside and unprotected can be far greater than hay producers realize.  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.  

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).

The amount of precipitation that falls on unprotected bales can affect storage losses.  However, precipitation alone is not a good indicator of projected losses.  Oklahoma State University researchers found that storage losses were related to precipitation combined with air temperature and humidity.  Much of the dry matter loss associated with outside storage is the result of microbial respiration where carbohydrates in the plant tissue plus oxygen are converted to carbon dioxide, water, and heat.  Read more about storage of big round bales by downloading the Oklahoma State University Fact Sheet BAE-1716 Round Bale Hay Storage written by Dr. Raymond Huhnke, Oklahoma State University Extension Agricultural Engineer.  (Note: Current prices of hay and storage materials may vary from those reported in this fact sheet.)

Source: Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist