  The effective coupling of QCD is measured by using the gauge configurations
produced by the MILC collaboration in which the Kogut Susskind (KS) fermion is
incorporated and by using that produced by the QCDOC collaboration in which the
domain wall fermion (DWF) is incorporated. We fix the gauge to the Landau gauge
and to the Coulomb gauge. The infrared effective coupling in the Coulomb gauge
agrees with the recent extraction at JLab, but that in the Landau gauge shows
infrared suppression. The suppression is expected to be due to the color
anti-symmetric ghost propagator which in the unquenched configurations has
stronger infrared singularity than the color diagonal ghost propagator. The
Coulomb form factor in the infrared depends on the kind of the fermion
incorporated in the system and the temperature. The quark has the effect of
quenching randomness and the fluctuation of the color anti-symmetric ghost
propagator is reduced in the unquenched configuration, and the Kugo-Ojima
parameter c is closer to 1 in the unquenched configuration than in the quenched
configuration.
