Electroweak measurements in the forward region at LHCb

W, Z and low mass Drell-Yan production cross sections in proton-proton collisions at $\sqrt{s} =$ 7 TeV have been measured with $W \to \mu \upsilon_{\mu}, Z \to \mu \mu, Z \to ee, Z \to \tau \tau $ and $\gamma^* \to \mu \mu$ channels in the LHCb detector. The cross section results are consistent with theoretical predictions calculated at next-to-next-to-leading order (NNLO) with different proton parton distribution functions (PDFs).