Selection for Improved Nutritional Quality of Alfalfa Forage1

Four diverse alfalfa (Medicagospp.) populations were screened in the field for nutritional quality. Acid detergent fiber of composite samples from first and second harvests was used to select for dry matter digestibility. First‐harvest percent transmittance, a Udy dyebinding procedure, was used to estimate crude protein concentration. Comparisons with standard cultivars showed that one cycle of selection was effective in reducing total cell wall, lignin, and amount of cell wall lignification and in increasing crude protein, hemicellulose (when expressed as a fraction of cell wall), in vitro dry matter digestibility, and in vitro cell wall digestibility in three of the four populations. Improved digestibility was associated with an increase in hemicellulose and a decrease in lignin fractions of the cell wall. Cellulose (when expressed as a fraction of the cell wall) did not change with selection. The mean crude protein concentration of the most improved population was 208 g kg−1, and total digestible dry matter was 775 g kg−1as compared to 199 and 756 g kg−1, respectively, measured for the mean of standard cultivars. These differences correspond to an increased crude protein yield of approximately 200 kg ha−1yr−1and an increased digestible dry matter yield of approximately 525 kg ha−1yr−1.