Dry matter loss resulting from respiration and leached nutrients often exceeds 30 percent in some areas.
Forage quality, especially digestible dry matter, often drops sharply. Also, weathered hay is less palatable to animals, which can greatly increase refusal and feeding loss.
As a result, in some cases half or more of the hay produced is unnecessarily lost. Many producers could easily and quickly pay for building a hay barn through savings realized by reducing outside storage losses.
From Forage-Livestock Quotes and Concepts, D.M. Ball
PHOTO 1: Hay stored in a barn
PHOTO 2: Hay stored outside in stacks.