Using simulated rainfall techniques to predict losses of forage dry matter using fiber constituents as internal markers, and to evaluate changes in nutritive value and ruminal DM degradability in wilting orchardgrass and bermudagrass forages

Hay producers in the US have long desired a set of general guidelines for management decisions when faced with the possibility that a wilting hay crop may become damaged by rainfall. Specifically, information describing losses of forage dry matter (DM) and changes in quality that occur in hay crops in response to rain damage are of major importance. Previous studies that have evaluated losses of DM and changes in nutritive value for rain-damaged forages have generally been limited to irregular and unpredictable natural events, or rather simplistic artificial application techniques. Recently a few scientists have adapted various types of rainfall simulation systems for these purposes. Rainfall simulation techniques offer unique opportunities to control the rainfall environment, and therefore more precisely identify variables that may affect the quality of the hay crop. Research reports describing the impacts of simulated rain damage to grass hay crops are limited. Therefore, a series of experiments were initiated to evaluate: (1) concentrations of fiber components, whole-plant ash, and acid detergent insoluble ash (ADIA) for their ability to serve as internal plant markers and accurately predict losses of DM in bermudagrass (Cynodon dactylon L. Pers.) and orchardgrass (Dactylis glomerata L.) hays that were damaged by simulated rainfall or machine-rinsing procedures; (2) the effects of simulated rainfall damage and post-rainfall drying method on predicted losses of DM, concentrations of fiber and N, and estimates of ruminal DM degradability in orchardgrass hay; and (3) the same effects described in (2) on wilting bermudagrass hay. Results of these trials indicate that forages that are damaged by rainfall during the wilting period exhibit losses of DM, increased concentrations of fiber and nitrogen, and decreases in estimates of ruminal DM degradability. Losses of DM and reductions in forage nutritive value probably represent losses of soluble, nonstructural carbohydrates that are leached from plant tissues by rain. While losses of these components clearly have negative impacts on the quality and digestibility of resulting hay, the inverse relationship between losses of soluble cell components and increasing concentrations of fiber constituents provide opportunities to use concentrations of fiber as useful internal plant indicators or markers of DM loss.