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Guest Opinions

Thinking Hay Storage

Written by Jeremiah Vardiman



By Jeremiah Vardiman, UW Extension Educator


The end is in sight for this year’s hay season with the last cutting being baled or the last few irrigations being applied. According to all the “hay for sale” ads in the classifieds, it has been a decent year for producing hay. As pickup and trailer loads of hay are shuttling this year’s bounty, it seems appropriate to talk about hay storage. 

Whether you produce or purchase hay or feed cows or other types of livestock, the purpose of properly stored hay is the same – to minimize storage losses and reduce fire risk. There are two types of storage losses that occur in hay, either dry matter or forage quality. The most important factor to control in hay storage is exposure to moisture, either internal or external, which can be controlled through bale condition, climatic factors and storage techniques. 

The first consideration for storage of hay is bale condition, also known as moisture content of the bale. Since a bale of hay consists of dry matter or plant material and water, it should be no surprise that there is a direct relationship between moisture content and dry matter loss. The more moisture or water in a bale, the greater the loss of dry matter to microbial activity, which can generate significant levels of heat that also lower forage quality, including both crude protein and digestible nutrients. As a general rule of thumb, hay baled at 15 to 20 percent moisture content will have less dry matter loss and maximize the overall nutrient quality of the bale. Any bale of hay that has 25 percent or greater moisture content will see significant dry matter and nutrient quality loss the longer it is stored.

After bale condition, the next thing to consider is the climatic factors, or weathering process, and storage techniques of hay. These two topics are generally well understood through simple observation. Nevertheless research has shown that hay stored on the ground, outside and fully exposed to the elements for a year can lose up to 22 percent dry matter, 14 percent in crude protein and 25 percent in digestible nutrients in the weathered portion of the bale. These losses result in less physical hay and lower quality hay available for feeding, resulting in more expense to the owner to replenish supplies and the nutrient quality through supplemental feeding.

So what can be done to minimize this storage loss? Protect the stored hay from moisture. Does that mean the hay has to be stored in a barn or shed? Barns and sheds are a good option, though not everyone can afford one. The ground and top portion of hay are the most vulnerable to weathering, therefore the most effort should be concentrated on protecting these portions. 

Here are some recommendations. First, store the hay on a surface that does not retain water and is well drained. A gravel base is a good option. Make sure the surrounding land drains water away from the hay and not towards it, and protect the top of the hay with a roof or tarp.

The other reason for proper storage of hay is to reduce fire risk. Hay bales can start on fire from external or internal sources. The internal source, also coined spontaneous combustion, happens in hay that is baled too wet. Hay that has moisture content of 25 percent or greater has a high probability of bursting into flames due to excessive heat generated by the microbial degradation process within the bale. Once the heat exceeds 150 degrees Fahrenheit, the chance of spontaneous combustion increases, especially when the heat is exposed to oxygen. However, this is not a concern for hay of proper moisture levels – between 15 and 20 percent – because even though the hay experiences the same heating process, it does not exceed 125 degrees Fahrenheit and therefore does not ignite into flames. Hay that is suspected of being too wet should be stored outside for approximately three weeks or until the bale has stopped generating excessive heat. Then the hay can be stacked as needed.

It probably goes without saying that hay can be ignited from external sources such as open flames, electrical malfunctions, lighting strikes, etc. Be mindful of where the hay is stored and potential risks associated with that area. Always remember that moisture is the biggest concern for storage losses and potential fire risks to stored hay. Even minimal storage effort, such as a tarp, can lead to ensuring better quality hay over a longer period of time.