Each harvest season brings concerns regarding storage options for hay.
"Indeed, producers need to find ways to prevent shrink losses in their bunkers and storage systems," said Karla Hernandez, SDSU Extension Forages Field Specialist.
As Hernandez explained, hay storage losses are around 5 percent when it is harvested at 15 percent moisture and stored under dry conditions. "Stored forages provide essential nutrients for livestock when pastures are inadequate and are a consistent feed supply for dairies, sheep flocks, cow/calf producers, and beef feedlots. However, some of these nutrients can be lost if forages are not stored properly," she said.

Types of storage losses
Stored forage can be subjected to dry matter and quality losses. She explained that losses of dry hay stored inside a barn are usually not a concern, however, when forage moisture exceeds 20 percent, even barn-stored losses tend to increase.
"Generally, each step in the forage-preservation process, like mowing, ranking, chopping, baling, storing, and unloading, will likely cause losses of forage dry matter," Hernandez said.
Losses can either be mechanical or biological. During hay-making, most of the losses are mechanical or weather damage, she explained. When putting up silage however, Hernandez said most losses occur during the storage and feed-out stages.
Round bales are usually subjected to greater losses than small rectangular bales because between baling and feed-out they tend to remain outside uncovered.
"No matter what type of storage and feeding methods are used, some losses are always possible," Hernandez said.
However, she added, by following the recommended storage methods, and careful handling, losses can be minimized saving livestock producer's time and money.
Factors to consider to avoid storage losses

Some important factors that impact outside storage losses are:
Bale Density – With dry hay (10-20 percent moisture), the denser the bale, the lower the amount of spoilage that occurs. The minimum density of round bales should be 10 pounds of hay per cubic foot.
Field operations – uniform swaths, sized to match the recommendations of the baler being used help produce uniform and dense hay bales.
Weather conditions – for hay stored outside, increased precipitation results in greater chances of storage losses.
Bale orientation and placement – large round bales should be stored in rows that are separated from each other to allow for moisture dissipation from the bales. At least 3 feet should be left between bale rows to ensure good air circulation. If possible, rows should be orientated north-south to allow more hours of exposure to the sun of the round bale's sides.

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source: igrow