To date, recommendations for distances between animal husbandry and residential zones have been based either on empirical assumptions, on studies of individual animal species, or on dispersion modelling with assumptions concerning source strength and odour dispersion. However, a cross-species approach with corresponding field investigations had been missing. The aim of this cross-species synthesis was to determine the attenuation of odour intensity with distance, to give insights into the variability between different types of farm odour sources with regard to their odour impact in the field.
The synthesis is based on datasets of farms with cattle and pig husbandry, as well as animal husbandry combined with biogas facilities. In the case of cattle, loose dairy housing systems with and without an outdoor exercise yard were compared. Pig farms with forced or natural ventilation, with multiple-area pens and outdoor exercise yards were also part of the study. The farms with cattle husbandry and biogas facilities, two of which additionally kept pigs resp. poultry, covered a wide range and variety of emitting surface areas. During down-wind plume inspections in the field, assessors recorded their odour perception and odour intensity. The mean odour intensity in the down-wind plume was explained with a linear mixed-effects model. The fixed effects distance, emitting area, wind speed, and the type of farm odour sources (animal species, type of housing and facility) were significant. The highest odour intensity resulted from the animal housing with cattle and pigs combined with a biogas facility, followed by biogas facilities with cattle, with cattle and broiler chickens and from pig housing with forced ventilation, without outdoor exercise yard. The investigated cattle farms were characterised by lower odour intensity; but the effect of the outdoor exercise yard was obviously. Farms with a larger number of animals, with spatially extended area sources, e.g. with outdoor exercise areas, in the case of pigs also with natural ventilation and multi-area surfaces resulted in a greater spatial plume extent. Differences of animal species became clear, in that pig husbandry was characterized by a higher odour intensity than the attenuation curves of cattle husbandry.
The identified relationship of odour-relevant sources, wind speed and odour perception in the plume will create a better understanding of factors, which impact odour in the field. The observed decrease of odour intensity with distance, the ranking of animal species, housing systems and source characteristics can serve as a basis to improve minimum separation distance and the siting of animal husbandry near residential areas.