  X-shooter, with its characteristics of resolution, spectral coverage and
efficiency, provides a unique opportunity to obtain spectra of the
highest-redshift quasars (z ~ 6) that will allow us to carry out successful
investigations on key cosmological issues, from the details of the
re-ionization process, to the evolution of the first galaxies and AGNs. In this
paper, we present the spectra of three z ~ 6 quasars: one obtained during the
commissioning of X-shooter and two in the context of our ongoing GTO programme.
Combining this sample with data in the literature, we update the value of the C
IV cosmic mass density in the range 4.5 < z < 5, confirming the constant trend
with redshift between 2.5 and 5.
