Effects of stocking density and environmental enrichment on behavior and fecal corticosteroid levels of pigs under commercial farm conditions

In intensive pig farming of Western and Southern Europe, welfare concerns are still often related to barren environments and crowded conditions. Pig producers need to balance the requirements to improve welfare conditions at farm with practical considerations. The aim of this study was to determine the extent to which the reduction of stocking density and the provision of suspended pieces of hard wood as environmental enrichment have an influence on both behavior and fecal corticosteroid concentrations in commercially housed growing-finishing pigs. A total of 640 growing pigs were arranged in a 2 × 2 factorial design with stocking density (high, 1.0 m2/pig and low, 1.5 m2/pig) and environmental enrichment (yes or no) as factors. Ten replicate pens were allocated to each treatment. Observations of behavior (instantaneous scan sampling) were made in each pen at 2-week intervals, when pigs were from 15 to 31 weeks old. Fecal samples were collected to determine corticosteroids concentration in the 40 selected pens. The pigs housed in low density showed a higher (although not significant) level of exploration of pen furniture than crowded pigs (10.11% vs. 8.53%, respectively; P = 0.09). Similarly, social interactions were observed more frequently (P ≤ 0.001) among the pigs in the enriched (10.27%) than in barren (6.69%) pens. The pigs housed in barren pens had greater incidences of tail biting (barren: 1.35%, enriched: 0.42%; P ≤ 0.01) and aggression (barren: 1.30%, enriched 0.61%; P ≤ 0.05). Crowded pig in barren pens spent less time moving (2.26%) compared to other treatments. Uncrowded pigs in enriched pens spent less time lying inactive (43.97%) and feeding (14.48%) compared to other treatments. Fecal corticosteroids doubled their concentration from the first (56.74 ng/g) to the last (108.10 ng/g) sampling date (P ≤ 0.001). The crowded pigs showed higher (P ≤ 0.001) concentration than the pigs housed in low stocking density (85.09 ng/g and 76.08 ng/g, respectively). No differences were found in corticosteroid concentrations between the pigs housed in barren and enriched pens. To conclude, the reduction of stocking density modified the pigs' behaviors and reduced the fecal corticosteroid levels, highlighting an improvement of welfare conditions. The provision of suspended pieces of hard wood modified the pigs' behaviors but did not exert relevant effects on fecal corticosteroid levels.