  Using lattice quantum chromodynamics (QCD) we perform an unquenched
calculation of the gluon propagator in Landau gauge. We use configurations
generated with the AsqTad quark action by the MILC collaboration for the
dynamical quarks and compare the gluon propagator of quenched QCD (i.e., the
pure Yang-Mills gluon propagator) with that of 2+1 flavor QCD. The effects of
the dynamical quarks are clearly visible and lead to a significant reduction of
the nonperturbative infrared enhancement relative to the quenched case.
