  A system of $N$ classical Heisenberg-like rotators, characterized by
infinite-range ferromagnetic interactions, is studied numerically within the
microcanonical ensemble through a molecular-dynamics approach. Such a model,
known as the classical inertial infinite-range-interaction Heisenberg
ferromagnet, exhibits a second-order phase transition within the standard
canonical-ensemble solution. The present numerical analysis, which is
restricted to an energy density slightly below criticality, compares the
effects of different initial conditions for the orientations of the classical
rotators. By monitoring the time evolution of the kinetic temperature, we
observe that the system may evolve into a metastable state (whose duration
increases linearly with $N$), in both cases of maximal and zero initial
magnetization, before attaining a second plateau at longer times. Since the
kinetic temperatures associated with the second plateau, in the above-mentioned
cases, do not coincide, the system may present a three-plateaux (or even more
complicated) structure for finite $N$. To our knowledge, this has never before
been observed on similar Hamiltonian models, such as the XY version of the
present model. It is also shown that the system is sensitive to the way that
one breaks the symmetry of the paramagnetic state: different nonzero values for
the initial magnetization may lead to sensibly distinct evolutions for the
kinetic temperature, whereas different situations with zero initial
magnetization all lead to the same structure.
