Ammonia and greenhouse gas emission from group-housed gestating sows depends on floor type

The ban by 2013 in the EU of individual accommodations for gestating sows and the renewed interest for litter systems could promote in the future the group-housing of gestating sows on litter. But what are the environmental impacts of this rearing technique? To answer this question, a study was scheduled to quantify pollutant gas emissions (nitrous oxide –N₂O–, methane –CH₄–, carbon dioxide –CO₂– and ammonia –NH₃–) according to floor type in the raising of group-housed gestating sows. The trial was carried out in experimental rooms located at Liège University (Belgium). Three successive batches of 10 gestating sows were used for this trial. Each batch was divided into 2 homogeneous groups randomly allocated to one of two treatments: concrete slatted floor or straw-based deep litter. The groups were kept separately in two identical rooms equipped with a pen divided into a lying area (slatted floor or deep litter) and five individual feeding stalls. The feeding stalls were equipped with front feeding troughs and rear gates preventing access to the stalls outside of the feeding time. Between each batch of sows, the pens were cleaned. In both rooms, ventilation was automatically adapted to maintain a constant ambient temperature. The gas emissions were measured 3 times (weeks 2, 5 and 8 of stay) during 6 consecutive days by infra red photoacoustic detection. Sow performance (body weight gain, backfat thickness, number and weight of piglets) was not significantly affected by floor type. With sows kept on slatted floor, gaseous emissions were significantly greater for NH₃ (12.77 vs. 9.05gd⁻¹sow⁻¹; P<0.001) and CH₄ (10.12 vs. 9.20gd⁻¹sow⁻¹; P<0.01), and significantly lower for N₂O (0.47 vs. 2.27gd⁻¹sow⁻¹; P<0.001), CO₂ equivalents (0.44 vs. 0.94kgd⁻¹sow⁻¹; P<0.001) and CO₂ (2.41 vs. 2.83kgd⁻¹sow⁻¹; P<0.001) compared to sows housed on straw-based deep litter. There was no significant difference for water vapour emissions (3.25 vs. 3.21kgd⁻¹sow⁻¹; P>0.05). In conclusion, the main environmental disadvantage of the deep litter system pointed to in this study was the greater N₂O-emissions and thus greater CO₂eq-emissions compared to slatted floor. However, the use of deep litter was related to reduced NH₃- and CH₄-emissions.