ASH CONTENT OF DETERGENT FIBERS IN FEEDS, DIGESTA, AND FECES AND ITS RELEVANCE IN FIBER DIGESTIBILITY CALCULATIONS

The influence of insoluble ash in diet, digesta, and fecal samples was evaluated. Ash-free values of neutral detergent fiber (NDF) and acid detergent fiber (ADF) for feed, digesta, and fecal samples were compar ed with uncorrected values of NDF and ADF in two digestibility experim ents. Six feed samples were selected at random along with four duodena l and two fecal samples; the latter two were a part of two digestion s tudies. The silica composition of feed samples was low with the except ion of oat hay and rice straw. Ash-free values of NDF and ADF for dige sta and fecal samples were lower than uncorrected values of NDF and AD F, and silica accounted for the majority of the differences. The use o f ash-free values of NDF and ADF in both digestibility experiments wit h dairy cows resulted in more realistic digestibility estimates and re duced the amount of variability associated with the calculation of the digestibility of NDF and ADF in the rumen and total digestive tract. The source of the insoluble ash was not identified but could have come from individual feedstuffs or the consumption of sand. Sample contami nation by silica and other ash components may influence NDF and ADF co mposition if the fiber residues are not ashed prior to calculation of NDF and ADF.