demonstrated to be a true, generic property of the Universe [@BKL70; @BKL82; @Montani]. However, while the dynamics of the early Universe has been essentially understood, its physical and thermodynamical nature is far to be under control. On one hand, quantum gravity effects are able of altering the standard dynamical features proposed in [@BKL82; @K93; @Mo95], giving rise to fascinating alternatives (see for instance [@Ash],[@Pal]) and particle creation effects can also be relevant [@Star; @Mo2001]. Calling for attention is also the string cosmology paradigm, as discussed for instance in [@Barrow]. On the other hand, such an extreme region of evolution exhibits a rapid expansion and non-trivial out-of-equilibrium phenomena become possibly important, including the appearance of viscous features in the cosmological fluid. More specifically, one usually distinguishes the bulk viscosity from the shear viscosity: while the former accounts for the non-equilibrium effects associated to volume changes, the latter is a result of the friction between adjacent layers of the fluid. As a matter of fact, shear viscosity does not contribute in isotropic cosmologies, whereas it may significantly modify the dynamics of an anisotropic Universe, as we shall see below. The simplest representation of a relativistic viscous fluid is provided by the so-called 