Can commercial pigs demonstrate the ‘when’ aspect of episodic-like memory?

This study aims to identify whether commercial pigs have the capacity for episodic-like memory – the awareness of ‘what’, ‘where’ and ‘when’ about an event.

Year of Publication2009

Demonstrating higher level cognitive functions in animals could have implications for their welfare. One such higher function is episodic-like memory, which can be demonstrated by showing that animals know ‘what’, ‘where’ and ‘when’ about an event. Little research on this exists in farmed animals, therefore, this study aimed to identify whether it is present in commercial pigs. Two groups of nine female Large White ×Landrace pigs aged 10-12 wk were initially trained, individually, that food was present in one of two hoppers, either to the left or right of a test pen, teaching them ‘what’ and ‘where’. After the training, the ‘when’ aspect of episodic-like memory was examined using 4 and 8 hr intervals. After 4 hr the feed would remain in the same hopper; however, after 8 hr it would be in the other hopper. This was alternated, with all pigs being fed (and tested) both 4 and 8 hr after the first feeding, on different days. Pigs had no access to food between tests. The ability of pigs to immediately choose their correct hopper when 4 hr had elapsed since feeding, but select the other hopper after 8 hr, would suggest pigs can distinguish ‘when’. In the first part of the study, pigs learned to immediately choose the correct hopper at a level which was highly significantly different from chance (‘t’-test; P < 0.001), demonstrating that they could easily distinguish ‘what’ and ‘where’. For the second part, demonstrating ‘when’, results were more equivocal. Group 1 made choices that were significantly (P < 0.01) different from chance after both 4 and 8 hr, while group 2’s choices were significant after 4 (P < 0.001) but not 8 hr. Results of this study suggest that commercial pigs may be capable of the ‘when’ aspect of episodic-like memory, although further research is required.

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