  We calculate neutrino cross sections from neutral current reactions in the
dense matter encountered in the evolution of a newly born neutron star. Effects
of composition and of strong interactions in the deleptonization and cooling
phases of the evolution are studied. The influence of the possible presence of
strangeness-rich hyperons on the neutrino scattering cross sections is
explored. Due to the large vector couplings of the Sigma-minus and
Cascade-minus, |C_V|~2, these particles, if present in protoneutron star
matter, give significant contributions to neutrino scattering. In the
deleptonization phase, the presence of strangeness leads to large neutrino
energies, which results in large enhancements in the cross sections compared to
those in matter with nucleons only. In the cooling phase, in which matter is
nearly neutrino free, the response of the Sigma-minus hyperons to thermal
neutrinos is the most significant. Neutrinos couple relatively weakly to the
Lambda hyperons and, hence, their contributions are significant only at high
density.
