  We compare orbits in a thin axisymmetric disc potential in MOND to those in a
thin disc plus near-spherical dark matter halo predicted by a $\Lambda$CDM
cosmology. Remarkably, the amount of orbital precession in MOND is nearly
identical to that which occurs in a mildly oblate CDM Galactic halo (potential
flattening q=0.9), consistent with recent constraints from the Sagittarius
stream. Since very flattened mass distributions in MOND produce rounder
potentials than in standard Newtonian mechanics, we show that it will be very
difficult to use the tidal debris from streams to distinguish between a MOND
galaxy and a standard CDM galaxy with a mildly oblate halo.
  If a galaxy can be found with either a prolate halo, or one which is more
oblate than $q \sim 0.9$ this would rule out MOND as a viable theory. Improved
data from the leading arm of the Sagittarius dwarf - which samples the Galactic
potential at large radii - could rule out MOND if the orbital pole precession
can be determined to an accuracy of the order of $\pm 1^o$.

Astrophysics