Acid Detergent Fiber as a percent of Dry Matter. Acid Detergent Fiber is a chemical analysis that determines the amount of residue (primarily cellulose, lignin and variable amounts of silica) remaining after boiling a feed sample in an acid detergent solution. The ADF value is more as a gauge than anything else in the model at this time. Revisions to the model focus on the use of uNDF at various time points as a determinant of digestibility.