The long and short of showers: Effects of shower duration on behaviour, thermal comfort and soiling of organic growing-finishing pigs with access to outdoor runs

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Showers can be used in the outdoor run to improve thermal comfort and provide environmental enrichment for growing-finishing pigs. Showers may also reduce ammonia emissions by preventing excessive soiling in summer. Few studies have addressed water cooling measures for pigs in systems with concrete outdoor runs, and none have considered the operation of showers outdoors. We therefore investigated the effect of showers in the outdoor run on pigs’ use of different pen areas, thermal comfort, and soiling of the pigs and the pen in multi-farm experiments in Austria and Switzerland. In a pilot experiment on three organic farms involving a total of 428 growing-finishing pigs in 15 groups with two to three assessment days each, we compared groups with access to showers to groups without showers. A subsequent larger trial (referred to as SHORT/LONG experiment) compared two different shower programmes (SHORT = 10-minutes; LONG = 30-minutes shower activation per hour), comprising a total of 472 pigs in 20 groups on three farms with six to seven assessment days each. The treatments SHORT and LONG were alternately applied with at least three replicates per farm. We assessed the pigs’ behaviour (activity, lying posture), respiratory rate and cleanliness as well as soiling of the pens on a group level. The pilot experiment revealed increased activity (p = 0.03) and reduced lateral lying (p = 0.08) in pigs with access to showers compared to pigs without, which supports the potential of showers to improve thermal comfort. In the SHORT/LONG experiment, we found interactions between treatment and outdoor temperature: The proportion of pigs under the shower (p < 0.01), lateral lying in the shower area (p = 0.01) and respiratory rate (p < 0.01) increased more with rising temperatures in treatment LONG than in SHORT. In both treatments, high temperatures increased the use of the outdoor run (p = 0.02) and the shower area (p < 0.001) as well as the soiling of pigs (p < 0.01), while at the same time reducing activity in the shower area (p = 0.02). Interestingly, fewer pigs were present in the shower area during and at the end of shower activation compared to the time before (p < 0.001), indicating avoidance of the water spray. This casts doubt on whether showers, apart from reducing heat stress, provide appropriate means to allow all aspects of species-specific thermoregulation. Our results suggest complex interactions between outdoor temperature, shower duration, pig behaviour, and soiling (with potential impact on ammonia emission), which require further investigation especially in open-air settings.