Abstract
Exercise yards are increasingly being attached to cattle housing in order to provide the animals with additional space for movement and contact with the external climate. The use of exercise yards in addition to the loose house usually causes an expansion in the soiled and hence emission-active areas. Besides this, we are dealing here with emission sources close to the ground, which are particularly exposed. Exercise yards were not previously taken into account in Switzerland when calculating the minimum distance to residential zones. The aim of this study was to highlight any effect of the exercise yard on odour impact by analysing an available dataset of loose houses with exercise yards using specific statistical methods. In addition, forcomparison with an experimental approach, the odour impact of an exercise yard with free flow over a uniform surface was determined. To this end, cattle excrement was distributed over an area of 100 m2. For the survey,ten dairy-cattle houses with exercise yards and isolated farm locations were selected. Nine farms had loose housing with resting cubicles and one had a deep-litter system. Eaves-to-ridge and forced-ventilation systems were all used. Animal populations varied between 20 and 40 livestock units. The emitting areas comprised 100 to 600 m², of which exercise yards accounted for between 50 and 180 m². The exercise yards had solid flooring and were permanently accessible.
For both the cattle housing and the test area, the odour impact was determined in the summer half-year by means of odour-plume inspections. Immediately after the first three inspection rounds, performed with a soiled exercise yard, the yard was covered with sheeting. Further inspections then followed, corresponding to the situation with no use of the exercise yard. Impact-side odour perception was recorded by trained assessors as odour intensity in intervals of ten seconds, via inspection rounds of ten minutes’ duration each.
The statistical analysis of the dataset with a linear mixed-effects model took into account the hierarchical structure with farm and survey date. The impact-side odour intensity was explained by a model with the influencing variables area, distance to source and wind speed. The odour impact of the test area was explained by analogy using a model consisting of distance and wind speed. The results from the test area and the surveys on the cattle farms demonstrate the odour relevance of enlarged surfaces. Only an analysis taking account of the hierarchical data structure with repeated measurements and fixed and random effects made it possible to derive relevant influencing variables on odour release and dispersion. A differentiation and consideration of total odour-relevant areas, and hence of exercise yards, is indicated in future in distance recommendations, in order to prevent odour complaints.
