Usage of outdoor runs and defaecation behaviour of fattening pigs

Access to an outdoor run improves the housing conditions of fattening pigs by an enlarged space allowance, access to different climatic conditions and environmental stimulation. One central conflicting issue regarding outdoor runs is the emission of harmful gases such as ammonia resulting from faeces and urine. However, by establishing appropriate functional areas in fattening pens, the area soiled by faeces and urine can potentially be reduced. Here, we investigated the usage of an outdoor run and the frequencies and locations of defaecation behaviour of fattening pigs kept in groups of ten in eight pens. Usage of the outdoor run was registered by scan sampling at the group level in three observation periods (pigs at 16, 19, and 22 weeks of age). Furthermore, in each pen, two focal pigs were individually marked and continuously observed for 24 hours in each observation period to record defaecation behaviour. At the group level, the fattening pigs used the outdoor run mainly during the daytime between 06:00 h and 20:00 h. A total of 99.4% of defaecation events occurred in the outdoor run, most often in the corner next to the wall of the barn. On average, 11.08 (± SD 3.06) defaecation events per pig per day were recorded, whereby the time of day significantly affected the relative frequencies of defaecation behaviour (GLMER, X12 = 4.11, P < 0.043). Fattening pigs defaecated more often during the daytime than during the nighttime. The number of daily defaecations decreased with age. In pens as used in our study, fattening pigs perform nearly all defaecations in the outdoor run and within a small area. This may enable technical possibilities to reduce ammonia emissions in pig pens with outdoor runs, such as regular cleaning of dunging areas by an automatic floor scraper.