Does the presence of a human affect the preference of enrichment items in young, isolated pigs?

Pigs may be housed individually in both production and research settings. Gregarious by nature, pigs kept in isolation may show behavioural and physiological signs of stress. In this study we investigated the preference of individually housed pigs, for social and non-social enrichments. Three enrichment items were compared: a mat (MAT), a companion (COM) and a mirror (MIR). Fourteen weaner pigs (Yorkshire×Landrace) were housed individually with continuous access to 4 adjacent pens. One pen was a control (CTRL) and had no enrichment; the others had one enrichment each, either a mat on part of the woven wire floor (MAT), a companion visible across the passageway (COM) or a mirror on one wall (MIR). Pigs spent more proportion of time (P=0.021) in the COM pen (0.65±0.07) compared to the CTRL pen (0.31±0.07) with the MAT pen (0.57±0.07) and the MIR (0.42±0.07) pen as intermediates. They also spent more total time engaged in investigative and inactive behaviours in the COM pen compared to the CTRL pen (P=0.007). A second analysis was performed to investigate changes in preferences in the presence or absence of a human in the room. The pens were then combined into two categories: social pens (COM and MIR) and nonsocial pens (MAT and CTRL). The probability of a pig being observed in the MIR pen when a human was present was significantly higher (P=0.0001), than when absent. Within the social enrichments, the probability of the animal being observed in either MIR or COM pen was not different (P=0.017). Our results confirm that preference studies may be highly sensitive to experimental conditions. Thus, the assumption that the most important preference is the one the animal spends most of its time with can be misleading. It appears that a mirror may be used by the animal for social support during periods of perceived threat, however further investigation is warranted.