The objective of this study was to determine how well changes in forage quality could be simulated during field drying for hay. Measurements of moisture content and three quality components were made during eight drying periods over three years. Samples were taken from forage swaths at one to four day intervals during drying period. Changes in total dry matter and its constituents were calculated from the measured/simulated changes in quality components. Comparison of simulated and measured changes were made for total losses and cumulative changes during each drying period. The simulated total dry matter losses were within the error limits of measurement for two of three rainfree and four of five prolonged drying periods. It was necessary to assume that loss of crude protein from plant cells was one-half as susceptible as the loss of non-protein cell contents
