Maize silage as enrichment material improves the welfare of growing-finishing pigs in environmentally-friendly pens

Provision of enrichment in welfare- and environmentally-friendly pig pens is important for sustainable pig production. The primary aim of the present experiment was to investigate the effects of maize silage as a singular enrichment compared to a combination of maize silage and chopped straw on behaviours important for determining pig welfare (play, locomotion, exploration, social contact, aggression, manipulation, eating, drinking, lying/sleeping, sitting/standing and nosing objects) in growing-finishing pigs (pigs, n = 432; batch, n = 2; pens n = 12 per batch). Secondly, the impact of drinker position (IN: two drinkers placed in the inside area; OUT: two drinkers in the outside area; IN_OUT: a drinker in each of the inside and outside areas; n = 8 pens per group) on pig behaviour was assessed. There were no statistically significant influences of enrichment treatments on behaviour. The OUT group performed less manipulation behaviour than the IN (mean difference = 2.65; 90 % highest density interval (HDI): 0.46, 4.84) and IN-OUT (mean difference = 2.88 HDI: 0.69, 5.15) groups, and drank more than the IN-OUT group (mean difference = -3.87; HDI: -6.76, -0.90). In addition, we found that a one standard deviation (∼ 2 days) increase in observation days/pig age significantly decreased manipulation (log coefficient = -0.32; HDI: -0.42, -0.22) and aggressive behaviours (log coefficient = -0.46; HDI: -0.57, -0.36), but there was an increase in drinking (log coefficient = 0.13; HDI: 0.09, 0.18) and nosing objects (log coefficient = 0.12; HDI: 0.06, 0.18). Significant associations were also found for batch (season), as well as correlations between behaviours. In summary, our results showed that pig behaviours during the growing-fattening period were similarly expressed in the maize silage and combined maize silage and chopped straw treatments, suggesting that maize silage in environmentally-friendly pig pens is adequate in ensuring welfare standards. Furthermore, placing drinkers in the outside area reduced manipulation between pen-mates, thus, could improve pig welfare.