Factors Affecting Volume and Specific Gravity Measurements of Neutral Detergent Fiber and Forage Particles

Pycnometers were used in this series of experiments to measure the specific gravity of the solid fraction in forage particles and to assess the effect of solubilization of DM on functional specific gravity and the specific gravity of the solid fraction. The removal of cell contents by either neutral detergent extraction or DM solubilization decreased functional specific gravity and the specific gravity of the solid fraction of particles. Solutes increased the specific gravity of gas-free distilled water in proportion to the amount of soluble DM dissolved. The average specific gravity of the solids in particles extracted by neutral detergent and the insoluble DM in alfalfa particles averaged 1.48 and 1.50, respectively. The effect of forage species and method of forage preservation on specific gravity of the solids in forage particles was minimal. However, during partial solubilization of DM, the loss of mass averaged 1.9 times the loss of volume, indicating that minerals were the primary solute responsible for the change in specific gravity of particles. The biological meaning of functional specific gravity is unclear because it excludes the liquid associated with particles. However, functional specific gravity of stem particles passing a 425-µm sieve was identical to specific gravity of the solids, indicating the absence of gas in these particles.