An animal slurry macerator (1) comprising a housing (2), a slurry chamber (3) in the housing (2) for receiving slurry from a slurry inlet (6) on the housing (2), a rotatable cutting plunger (4) in the slurry chamber (3) for macerating slurry, and a plurality of slurry outlets (7) on the housing (2) for discharging macerated slurry from the slurry chamber (3) wherein the slurry outlets (7) are provided with air-valves (8) at the housing (2) to facilitate air flow through the slurry outlet (7).
