Hay can be damaged by rain, snow, wind, and ice if it is stored outside during the fall and winter. Round bales, on average, will lose up to one fourth of its nutrients when stored outside. If the bale was stored properly or inside, this can be reduced to only 10 to 15 percent.
How do you stack or store your bales? In a line so the twine sides touch or are they stacked. If this is one of the ways you store them, extra spoilage can occur at the places where the bales are touching because rain, snow, and ice gather at these spots instead of running off the bale. If you were to line bales up end to end, you will have less spoilage.
Do you line your bales up north and south, or east and west? By lining them up east and west, there will be a better chance of having drifts on the south side of the bales. Bales that are lined up next to fence-lines or trees can get extra snow. When the snow melts, it can soak into the bales or make the ground muddy. If you line your bales up, line them up north and south so there will be fewer drifts and they will dry quicker because they will be exposed to the sun and winds on both sides of the bale. Make sure you put your bales on higher, well drained ground so that the water can drain away from them. You can use crushed rock, railroad ties, or even pallets to help keep the bottom of the bales dry. This will also reduce the problems you might have getting to your hay or moving them due to the snow drifts or mud.
By pre-planning, you will be able to have higher quality hay and less frustrations.
Source: www.extension.org