Nitrogen Fractions in Selected Feedstuffs

Abstract

N 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 N solubility. N solubility varied with type of solvent. Borate-phosphate buffer was more stable than other solvents. Borate-phosphate buffer had a correlation coefficient of 0.92 with insoluble N obtained with autoclaved rumen fluid. Insoluble N 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 N solubility. In most feedstuffs, a large fraction of soluble N was in the form of nonprotein N. Oats and peanut meal contained a significant amount of soluble true protein (43.3 and 24.3% of total N). Neutral detergent insoluble N and acid detergent insoluble N content of feed samples varied among feedstuffs and were not a constant proportion of neutral detergent or acid detergent fiber.