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Chemical Composition of the Cell-Wall Constituent and Acid Detergent Fiber Fractions of Forages

Nutrition Division, Department of Animal Sciences, Rutgers—The State University, New Brunswick, New Jersey

ABSTRACT

Cell-wall constituent (CWC) and acid detergent fiber (ADF) fractions of forages were analyzed for their chemical constitution. For 14 grasses, four alfalfas, and three alfalfa-grass mixtures, respectively, cellulose plus lignin represented 51, 69, and 58% of the total CWC. Acid-detergent fiber as an entity followed the same trend. In CWC crude protein (N x 6.25) and ash residues were present, and hemicellulose was calculated. Of the original plant content the CWC fraction recovered 95% of ADF, 94% of cellulose, 91% of lignin, and 27% of crude protein. For all forages, cellulose represented a consistent portion (79.0±0.68%) of total ADF. Lignin content of ADF for grasses was 10.6±0.69%, significantly different (P < .01) from 16.3±0.97% of alfalfas and alfalfa-grass mixtures. Cellulose plus lignin acounted for 90.2±0.68% for grasses and 94.2±0.94% for alfalfas and alfalfa-grass mixtures of the respective total ADF fractions, and crude protein plus ash residue appeared constant. Acid detergent fiber chemical analyses for cellulose, lignin, crude protein, and ash accounted for 95% of the total ADF for grasses and 99% for alfalfas and alfalfa-grass mixtures. Acid detergent fiber recovered 92% of the original plant cellulose and 6% of crude protein. Acid detergent fiber minus lignin c predicted cellulose C for grasses, using regression equation C = 4.56 + 0.81 c; for alfalfas and alfalfa-grass mixtures C = 5.66 + 0.83 c. Cell-wall constituent, and particularly the ADF fraction, represented a more complete forage entity than crude fiber.