A ventilation duct system (1,24,34) and method serve for minimizing air pollution in and/or around an animal habitat structure (25,33,52) with at least one animal habitat surface (3). The ventilation duct system (1,24,34) is located at least partly below the at least one animal habitat surface (3) and comprises waste receiving means (2) configured for receiving waste (17,20,32) from and/or through at least a part of the at last one animal habitat surface (3). The ventilation duct system (1,24,34) provides an air pressure gradient across the width of the waste receiving means (2), which air pressure gradient is generated by a pressure difference between a first long side (10) and an opposing second long side (11) of the waste receiving means (2). The ammonia concentration is almost completely kept at floor level and in the slurry pits, and the breathing air in the room above the slatted floor is thus ventilated without admixing the unpleasant gases from the animals.