  The resonant production of keV sterile-neutrino dark matter mainly takes
place during the QCD epoch of the early universe. It has been argued that it
could be strongly affected by the opacities (or damping rates) of active
neutrinos, which receive non-perturbative QCD-contributions. We find that for
lepton asymmetries $ n_{ L_\alpha } /s $ below $ 10 ^ { -6 } $ the opacities
significantly affect the sterile-neutrino yield, but that for larger
asymmetries, which are necessary for producing a significant fraction of the
dark matter, the yield is insensitive to changes of the opacities. Thus
non-perturbative QCD contributions to the opacities at temperatures around 160
MeV will not affect this dark matter scenario. We obtain larger
sterile-neutrino yields than previous studies, and thus weaker lower limits on
the active-sterile mixing angle from Big Bang Nucleosynthesis.
