Potential ammonia emissions from straw, slurry pit and concrete floor in a group housing system for sows

To assess the contribution of straw bedding, concrete floors, slats, and slurry in the pits to ammonia emission in a straw-bedded group-housing system for sows, the ammonia volatilisation response of urination on the potential emitting surfaces from a sow house was studied under laboratory conditions. Ammonia is mainly produced by hydrolysis of the urea in the urine: a process that depends on the characteristics of the surface of the emitting area. For the study, substrate samples were obtained from the surfaces of a concrete floor in the walking alley (A), slurry pits under the drinking area and the waiting area (D and W) and from the straw bedding (S1, S2, S3). The latter represented straw with respectively a small (S1), an average (S2) and a high (S3) content of slurry dropped by the sows. The controls were a sample of slurry from a reference conventional housing system with sows kept individually on partly slatted floors (R), and a sample of unsoiled fresh straw from the farm depot (S0). After sprinkling 150 ml of urine on each sample, the ammonia volatilisation (E in mg), maximum volatilisation rate (rmax in mg/h) and time of occurrence of the maximum volatilisation rate (tmax in h) were measured during 7 days. Paired comparisons of the predicted means were based on standard error of differences (SEDs, probability P0·05) and most from the slurry from the reference system (1686 mg, P0·05). The highest volatilisation rate occurred from the concrete floor in the walking alley (17·5 mg/h, P>0·05). The volatilisation rate peaked soonest with heavily soiled straw, slurry in the pit under the waiting and drinking area, concrete floor and slurry from the reference system, and latest from unsoiled straw (P>0·05). The results reveal that in a sow house with straw bedding, the largest source of ammonia emission is a urine puddle on the concrete floor in the walking alley, and the smallest is a urination on straw, irrespective of the slurry content of the straw. Only at high slurry contents in the straw bedding does the rate at which ammonia is produced from urea increase. The implication is that straw bedding in a group-housing system for sows decreases the ammonia emission per m2 after a urination; however, its effect on other gaseous emissions remains to be clarified