  We have performed extensive zero-field thermal conductivity measurements on
single crystal samples of \LiHoF and \LiYHoF below $2.3 K$. By comparing these
data to a single ion scattering model, we have shown that the thermal
conductivity of \LiYHoF is dominated by simple single-ion scattering while that
of \LiHoF shows additional contributions, possibly associated with collective
spin excitations. No entirely satisfactory model, however, is available to
explain the thermal conductivity of the ferromagnet.
