  In the context of quintessence, the inclusion of new degrees of freedoms to
the matter sector might produce additional imprints on cosmological observables
while keeping the scalar field responsible for the quintessence and the
standard matter minimally coupled to gravity. We investigate this premise by
including a canonical SU(2) Yang-Mills field to the total content of the
universe coupled to the standard quintessencial field by a disformal
transformation. The effects of the gauge field are studied in an anisotropic
background configuration in order to allow for more general outcomes. The
background dynamics study is addressed by a dynamical system analysis from
which novel anisotropic scaling solutions with a non-vanishing gauge field are
obtained. After establishing the dynamical character of the fixed points, the
phenomenological consequences of the model are assessed by means of a numerical
analysis. An interesting result to be confronted with observations is a
transient matter-radiation phase for the gauge field dynamics. We have also
quantified the redshift-dependent contribution of the gauge field in the form
of dark radiation during the radiation era to the effective number of
relativistic species. This depends essentially on the initial conditions and,
more importantly, on the disformal coupling function. Phenomenological
couplings and the Abelian version of the model are discussed as well to check
the generality of our results.
