We derive hydrodynamic equations for nematic ferrofluids (ferronematics) in
the limit that the magnetic degree of freedom has relaxed to its equilibri
um value. We concentrate on novel dynamic effects linear in the magnetic fi
eld. We show that flow alignment, heat conduction, diffusion, thermodiffusi
on, viscosity and director reorientation are all modified by the presence o
f an external field. In particular, the new effects describe reversible (ir
reversible) couplings, where the conventional effects are irreversible (rev
ersible). We discuss, how these effects can be measured. In principle, this
description is applicable to conventional nematics, too, although huge mag
netic fields are expected to be necessary for detecting the new effects in
this case.