Rooting for feed: Mixing corn pellets into rooting material tends to increase the presence of grower and finisher pigs in the rooting area but not its cleanliness

Exploratory behaviour is an essential part of the behavioural repertoire of pigs. Providing pigs with a rooting area filled with appropriate material enables such behaviour and is therefore considered to improve animal welfare. Managing the hygiene of a rooting area, however, is often challenging when pigs use it also for elimination. Mixing corn pellets into the rooting material could increase use and exploration while reducing elimination behaviour. To investigate this hypothesis, we constructed rooting areas filled with compost produced from garden waste in four pens on a commercial organic farm. We compared two experimental pens (E) with rooting areas filled with compost, in which we mixed 2 kg of corn pellets every morning, with two control pens (C, rooting areas filled with compost only). The experiment started in October 2019 and lasted 34 weeks with seven replicates in total. Group size ranged between 21–35 pigs (N = 386). We registered behaviour once a week through direct observations of the complete outdoor area and additional video recordings of the rooting area. Behavioural variables of interest were activity status (i.e. standing/sitting or lying), rooting, agonistic and play behaviour. We assessed cleanliness of the rooting material via visual scoring and chemical analysis of compost samples. The latter included tests on dry matter content, conductivity, and ammonium concentration. Data were analysed with linear mixed-effects models. Results showed that there was a tendency for a higher total number of pigs in the rooting area in E than in C (p = 0.06). In E, more pigs were lying in the rooting area than in C (p = 0.04). There was no difference between treatments in rooting behaviour. In addition, the overall use of the outdoor run did not differ between treatments. Time of day influenced all recorded behaviours in the rooting area (p < 0.001). With increasing temperature, more pigs were present in the outdoor run (p < 0.001) and in the rooting area (p < 0.01) for both treatments. Conductivity and ammonium concentration in the compost increased the longer the compost remained in the rooting area (p < 0.001), but there was no difference between the two treatments. We conclude that mixing corn pellets into rooting material increases the use of the rooting area by heightening the overall presence of pigs in it but not its cleanliness.