Viscous properties of pig cecal contents and the contribution of solid particles to viscosity

Objective It is believed that solid particles are not responsible for digesta viscosity. However, solid particles are responsible for the viscosity of whole blood and fiber suspension such as wood pulp. Therefore, we measured viscosity of gut contents with and without solid particles. We also determined the contribution of solid particles to viscoelastic characters of gut contents. Methods We measured the coefficient of viscosity, shear rate, and shear stress of pig cecal contents by using a tube-flow viscometer before and after removal of particles. Results The coefficient of viscosity of intact pig cecal contents was negatively correlated with shear rate, a typical character of non-Newtonian fluids. The removal of solid particles from the contents resulted in a Newtonian fluid with very low viscosity. Conclusion Solid particles were mainly responsible for the viscoelastic character of pig cecal contents. Accordingly, the contribution of indigestible solid food components, sloughed epithelial cells, and bacterial cell bodies to the viscosity of gut contents should be re-evaluated.