  Thermal conductivity measurements have been performed on the superconducting
ferromagnet UCoGe down to very low temperature and under magnetic field. In
addition to the electronic quasiparticle thermal conductivity, additional
contributions to the thermal transport are detected: they are sensitive to the
amplitude and direction of the magnetic field, and at low temperature, they
display a strong anisotropy with the heat current direction. We identify these
contributions as arising from magnetic fluctuations. Detection of such
fluctuations on the thermal transport in 3D weak ferromagnets is very rare if
not unique, and pledges for a strongly itinerant character of the magnetism of
UCoGe.
