  The radiative component of the Universe has a characteristic impact on both
large scale structure (LSS) and the cosmic microwave background radiation
(CMB). We use the recent WMAP data, together with previous CBI data and 2dF
matter power spectrum, to constrain the effective number of neutrino species
$N_{eff}$ in a general Cosmology. We find that $N_{eff}=4.31$ with a 95 per
cent C.L. $1.6 \le N_{eff} \le 7.1$. If we include the $H_0$ prior from the HST
project we find the best fit $N_{eff}=4.08$ and $1.90 \le N_{eff} \le 6.62$ for
95 per cent C.L. The curvature we derive is still consistent with flat, but
assuming a flat Universe from the beginning implies a bias toward lower
$N_{eff}$, as well as artificially smaller error bars. Adding the Supernovae
constraint doesn't improve the result. We analyze and discuss the degeneracies
with other parameters, and point out that probes of the matter power spectrum
on smaller scales, accurate independent $\sigma_8$ measurements, together with
better independent measurement of $H_0$ would help in breaking the
degeneracies.
