Ammonia emission from individual- and group-housing systems for sows

Abstract

Given that freedom of movement improves sows' welfare, the implications for the emission of ammonia of keeping sows in groups instead of individually were investigated. Three housing systems were compared: System A, with 64 sows kept individually in feeding stalls with 2.8 m2 surface area per sow; System B, with 62 group-housed sows, free access stalls with 3.3 m2 surface area per sow; System C, with 65 group-housed sows, electronic sow feeders and with 3.4 m2 surface area per sow. The sows in Systems A and B were fed simultaneously twice a day at 7:30 and 15:30 h. In System C the sows were fed sequentially once a day from 15:30 h onwards. The study was carried out in winter during three one-week periods. Average outdoor temperature was 3.7 degrees C. The average ambient temperatures recorded in the houses were thermoneutral: 19.8 degrees C for System A, 19.2 degrees C for System B and 19.0 degrees C for System C. The average ammonia emission per sow was 0.72, 0.62 and 0.70 g hour-1 for the systems A, B and C, respectively. For the systems A, B and C this implied that 23, 20 and 23% of the nitrogen intake was emitted as ammonia nitrogen, respectively. The emission from System B was significantly less (P<0.05). The diurnal pattern of the ammonia emissions from Systems A and B were biphasic and were related to feeding times. In System C the diurnal pattern had a more monophasic course related to the feeding time in the afternoon with an additional small peak in the morning after the lights were switched on. The diurnal pattern of ammonia emission from sow houses was related to the feeding schedule. Under thermoneutral conditions, giving sows a larger area at their disposal - such as with group housing - did not imply an increase in ammonia emission.