  We evaluate the impact of recent SeaQuest (E906 experiment) data on dimuon
production in proton-deuteron and proton-proton collisions on parton
distribution functions (PDFs). We find these data in a good agreement with the
QCD predictions based on PDFs fitted to the Tevatron and LHC data on forward
production of $W$ and $Z$ bosons. As a basis for this study we use the ABMP16
PDF fits and show that they turn out to be compatible with the SeaQuest data,
and that these data have constraining power, allowing to reduce the
uncertainties on the isospin asymmetry of the light-sea-quark distribution at
large longitudinal momentum fraction $x$. We discuss the nuclear corrections
needed to describe the deuteron and show that they affect the theoretical
description of the proton-deuteron Drell-Yan cross section at the level of
$\mathcal{O}(0.5 - 1)$\%. We also comment on the compatibility of the SeaQuest
results with other state-of-the-art PDF fits and show that these data are in
clear disagreement with models proposing an SU(3)-flavor symmetric quark sea.
Finally, we perform a comparison between the second Mellin moments of the
light-quark PDFs and recent results from various lattice QCD computations,
which demonstrates good compatibility, albeit limited by the uncertainties
inherent in current lattice QCD simulations.
