Meeting ethological needs – Effects of straw and roughage on attractiveness of outdoor run and behaviour of organic fattening pigs

• Providing substrate in a concrete outdoor run improved pig welfare. • Substrate allocation increased the presence of pigs outdoors. • Provision of substrate in a roofed area promoted creation of functional zones. • Weather and temporal factors also influenced pig behaviour and outdoor run use. Organic pigs must have permanent access to an open-air space, which typically consists of a barren concrete outdoor run. One way to improve the attractiveness of the outdoor run for pigs and facilitate the establishment of functional zones is through allocation of rooting or roughage materials in this pen area. Accordingly, we investigated the effects of straw (rooting material) and maize silage (roughage) provided under a roof in a concrete-floored outdoor run on the behaviour of organic fattening pigs raised in large groups. In one typical Danish commercial farm, we compared three adjacent, similarly sized pens. Each pen contained an indoor area and an outdoor run. Each outdoor run was divided by a 1 m-high concrete wall into an unroofed area and an area covered by a roof, where substrate could be allocated. One pen received no material under the roof (control), the second pen received straw, and the third pen received maize silage. The study took place from June 2021 to July 2022 and involved 8 batches of pigs. The population size per pen at arrival was (average ± standard deviation) 384 ± 22 pigs, weighing 37 ± 4.8 kg. Pigs were sent to slaughter when their liveweight was approximately 115 kg, approximately 3 months after insertion. Based on footage, the number of pigs present in each area of the outdoor run, and of these the number of pigs in each body posture (lying; sitting; upright) and the number of pigs displaying activity behaviours when standing (exploring the ground; other behaviours than ground exploration) were instantaneously sampled at 10 min intervals from 09:00 h to 16:00 h on days 1, 7, 21, 35, 49, and 63 relative to the batch insertion. More pigs were seen in the roofed area of the outdoor run when either straw or roughage were allocated. Additionally, provision of straw induced more resting in the roofed area whereas allocation of roughage stimulated more ground exploration in the roofed area compared to control pens. Secondarily, pig's activity and outdoor run use were influenced by temporal effects (i.e., experimental day) and weather variations. Thirdly, a pilot study suggested that pigs compete for access to an enriched roofed area. Our study demonstrated the possibility of meeting the behavioural needs - and improving the welfare – of organics pigs housed indoors with access to outdoor run by providing roughage or bedding materials in a roofed area of the outdoor run.