Scattering amplitudes in gauge theories display important applications for the calculation of observables in the physics that the LHC delivers and, also, formal properties where mathematical aspects are considered. In this talk we consider relations among scattering amplitudes that are obtained as a consequence of the duality between colour and kinematics. These relations are obtained from Jacobi-like identities of kinematic numerators. Hence, we show that the generation of off-shell currents, with a clever choice of the gauge, allows for finding integral relations as a byproduct of this duality. On top of it, we rely on the loop-tree duality formalism to systematise the derivation of these relations. Analytic examples in QCD are presented.