  The ratios of $p/\pi$ at large transverse momentum in central $Au+Au$
collisions at RHIC are studied in the framework of jet quenching based on a
next-to-leading order pQCD parton model. It is shown that theoretical
calculations with a gluon energy loss larger than the quark energy loss will
naturally lead to a smaller $p/\pi$ ratios at large transverse momentum in
$Au+Au$ collisions than those in $p+p$ collisions at the same energy. Scenarios
with equal energy losses for gluons and quarks and a strong jet conversion are
both explored and it is demonstrated in both scenarios $p/\pi$ ratios at high
$p_T$ in central $Au+Au$ collisions are enhanced and the calculated ratios of
protons over pions approach to the experimental measurements. However, ${\bar
p}/p$ in the latter scenario is found to fit data better than that in the
former scenario.
