Mixer vehicle is typically a tractor drawn and powered trailer for mixing and distribution of bulk materials such as farm animals feedstuffs. It comprises a semi-cylindrical body (10) having a side discharge opening (22) with a single longitudinal agitation rotor (36) centred therein, the rotor having helical sweep bars (40) rotating close to the body wall in at least the body part not occupied by the opening acting as a skeleton auger driving material along the body into its discharge zone, and a lesser diameter return auger (50) in the latter zone acting to return material from that zone so that the material is circulated for mixing. When a door (28) is opened the action of the rotor discharges the material through the opening where it may be further acted on by a faster feed-out rotor (34).