Nitrogen Fractions in Selected Feedstuffs

in selected feedstuffs was fractionated based on solubility in mineral solvents and detergent solutions. Six solvents with either a continuous mixing procedure at constant temperature or an intermittent mixing procedure at room temperature were compared for nitrogen solubility. Nitrogen solubility varied with type of solvent. Borate-phosphate buffer was more stable than other solvents. Borate-phosphate buffer had a correlation coefficient of .92 with insoluble nitrogen obtained with autoclaved rumen fluid. Insoluble nitrogens obtained by continuous or intermittent mixing techniques were not significantly different. The latter procedure is simple and avoids the need for special extraction equipment for estimation of nitrogen solubility. In most feedstuffs, a large fraction of soluble nitrogen was in the form of nonprotein nitrogen. Oats and peanut meal contained a significant amount of soluble true protein (43.3 and 24.3% of total nitrogen). Neutral detergent insoluble nitrogen and acid detergent insoluble nitrogen content of feed samples varied among feedstuffs and were not a constant proportion of neutral detergent or acid detergent fiber. aBicarbonate-phosph ate buffer bBurrough's mineral mixture diluted to 10% with distilled water. CMcDougall's artificial saliva. d. 15 M NaCI.