  In analogy with the load and the metage in hydrodynamics, we define
magnetohydrodynamic load and magnetohydrodynamic metage in the case of
magnetofluids. They can be used to write the magnetic field in MHD in Clebsch's
form. We show how these two concepts can be utilised to derive the magnetic
analogue of the Ertel's theorem and also, how in the presence of non-trivial
topology of the magnetic field in the magnetofluid one may associate the
linking number of the magnetic field lines with the invariant MHD loads. The
paper illustrates that the symmetry translation of the MHD metage in the
corresponding label space generates the conservation of cross helicity.
