It can be impractical for farmers to provide pain relief to livestock following husbandry procedures such as castration and tail-docking, particularly in pasture-based systems because animals need to be repeatedly gathered to handling facilities and restrained. We investigated whether voluntary consumption by lambs of an analgesic incorporated into feed can achieve pain relief following surgical castration and hot-knife tail-docking. Sixty-four, singleton, male Merino lambs were randomly allocated to one of four treatment groups: sham castration and tail-docking (S), castrated + tail-docked + no pain relief (C), castrated + tail-docked + flunixin in feed (4.0 mg/kg, CF) and castrated + tail-docked + flunixin injection (2 mg/kg, CI). Haematology, cortisol, and plasma haptoglobin concentrations were measured before and up to 48 h after treatment. Lambs also had their scrotal and tail wounds scored based on severity of swelling and wound appearance, with 2 being a healed wound and 8 being severe swelling and evident necrosis and pus. Behaviours were recorded by video for 12 h after treatment. Lambs in the CF and CI groups displayed fewer active pain avoidance behaviours (P