The force of raindrops hitting drying hay disconnects leaves from the stem. The wetting and drying process increases the potential for leaf shatter. Rain-damaged hay can be brittle after drying, so it is more susceptible to loss during raking or baling. Extra operations may also be necessary to dry the rewetted hay, and these may increase mechanical losses and reduce forage quality. Leaching of soluble nutrients is the primary cause of quality loss.
Rain leaches the more soluble, highly digestible nutrients from hay.
It leaches some of the soluble protein and reduces the digestibility of the remaining protein. As a result, rain damage decreases digestibility and increases fiber concentration. Rainfall can cause additional losses by prolonging respiration. After it is cut, hay continues to respire until its moisture content drops to less than 40 percent. Rain rewets the forage and allows respiration to continue.