When deprived of play, as they are in factory farms on the crowded slatted pens, piglets do not grow into normal pigs.
Play is found mainly in the most cognitively complex and adaptable non-human species, such as primates, dogs, dolphins and birds. It also exists in fish and reptiles and complex invertebrates such as octopus. Play appears to be a marker of cognitive complexity.
Piglets are extremely fond of play, with wide and quite complex types of play involving other pigs and objects. Pigs commonly shake and carry objects (sticks, balls) and toss straw. They wave their head, scamper, jump, hop, paw, pivot, gambol, flop, play fight, push and run after each other (play tag), in a similar way to dogs (32).
According to the authors of a 2015 review of pig cognition, Lori Marino and Christina Colvin:
“Play in pigs not only satisfies a need for exploration and discovery, it is also critical for healthy development. Play is best stimulated by diverse, hands-on, and renewable objects and materials. So important is this need that insufficient opportunity to explore leads to behavioural abnormalities” (32).
Unsurprisingly, it has been documented that piglets born in farrowing crates do not develop socio-cognitively as well as those given freedom and an interesting environment; but also sadly, the crated piglets were emotionally depressed (32).