Could pigs have unidentified behavioural needs that warrant inclusion in future welfare assessments?

A growing body of research suggests that in addition to pigs’ known behavioural needs, some other behaviours may also be innately motivated, and thwarting them may cause frustration. Here, we review the literature on potential candidates for “new” behavioural needs and present our recent findings on nest-oriented behaviours. One candidate is wallowing, which literature suggests may have emotional significance beyond thermoregulation. Pigs spend time in water even at optimal temperatures and work to gain access to wallowing, suggesting potential similarity to dustbathing in poultry. We also discuss literature on potential significance of examining novelty and using olfaction. Our experimental contribution involves nest-oriented behaviours. They have been observed in sows building farrowing nests, piglets burrowing in the farrowing nests and pigs of both sexes building resting nests, but their welfare-relevance has only been studied in sows before farrowing. We collected descriptive data on pre-rest behaviours in intensively farmed pigs with no bedding. In Experiment 1, we observed 167 gilts on video for 2 h, finding that 92% of events of settling to recumbency started with oral-nasal contact, mainly at the floor (52%) or another pig (31%). In Experiment 2, we provided 128 finishing pigs with pieces of wood and 51 suckling piglets with sisal ropes. Each animal was observed once on video until recumbent and immobile, presumably asleep. Of the finishing pigs, 14% inserted the head or body under wood for 2 to 19 seconds before lying down; 3% remained under it when immobile. Of the piglets, 16% inserted the head or body under rope for 3 to 25 seconds before lying down; 14% remained under it when immobile. We conclude this may reflect a motivation to manipulate nest materials. Further research is needed on the welfare-relevance of these behaviours and whether they require inclusion in welfare assessments of the future.