The ventilation is judged more favourable the higher the stack and the larger the outlet velocity. In this way a transport of odorants into the wake of the building should be prevented. Outlet openings below rooftop or in the side walls are therefore considered almost as unfavourable as natural ventilation. Odour develops mainly from the duration the manure is kept in the building, the use of straw, and the air flow pattern. Odour development inside the livestock building is reduced if manure is removed frequently, straw is used, and air speed above the manure surface is low.
Poultry is treated separately.
For all the other animals, a differentiation between solid and liquid manure systems can be undertaken. Mechanical solid manure systems with closed manure removal show the lowest odour emissions. Deep litter systems are judged more favourable if the duration the manure is kept inside the building is short. Compared to ventilation system and manure treatment, its weight with values between .05 and .20 is lowest. The odour pollution around the source is assessed by taking into account the wind distribution, orographic influences, and given land use categories.