  We revisit the calculation of relic density of dark matter particles
co-annihilating with a top or bottom partner, by properly including the QCD
bound-states (onia) effects of the colored partners, as well as the relevant
electroweak processes which become important in the low mass region. We
carefully set up the complete framework that incorporates the relevant
contributions and investigate their effects on the cosmologically preferred
mass spectrum, which turn out to be comparable in size to those coming from the
Sommerfeld enhancement. We apply the calculation to three scenarios: bino-stop
and bino-sbottom co-annihilations in supersymmetry, and a vector dark matter
co-annihilating with a fermionic top partner. In addition, we confront our
analysis of the relic abundance with recent direct detection experiments and
collider searches at the LHC, which have important implications in the
bino-stop and bino-sbottom scenarios. In particular, in the bino-stop case
recent LHC limits have excluded regions of parameter with a direct detection
rate that is above the neutrino floor.
