The farmer-researcher @kereonnec made a discovery this week, his pigs curl their tails to the right or to the left. Why do they do this? This is the topic of #Pigbasics n°1: laterality.
https://twitter.com/kereonnec/status/1353806646292738048?s=20
Written with @LateraLiterally. Thank you 🥰.
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2. What is laterality? It’s the fact that brain and body are asymmetric. The right hemisphere controls the left part of the body and the left hemisphere controls the right one. This enables task sharing between both hemispheres and hence an optimized brain function.
3. Laterality can be measured at the individual level: one measures side preferences during motor tasks for a population, species, breed. For example, in humans, there is a majority of right-handers!
4. Thus, while observing behaviour, on can determine which hemisphere is active and which function is used (learning, emotions,…), and one can identify the “preferred” hemisphere of an individual as well.
5. So, what about our pigs? Did you ever notice that some pigs spontaneously turn their tail to the right or to the left? Like Adrien’s pigs. Some sows lay on the left side during lactating, others on the right side.
6. Yes, there are right-biased, left-biased and ambilateral pigs!
They rather use the ride side of their body, or the left, or both… This is observable according to how they use their snout, eyes, feet or to how they turn their tail.
7. This was the topic of @LateraLiterally during her PhD works, to provide a first investigation of pig laterality! Charlotte’s studies show that pigs are lateralized for using their snout. A majority were right snouted (42%) or left snouted (38%), and a minority were ambilateral
8. Surprisingly, a majority of pigs in the population turned their tail to the right (62%)! In contrast, during a stepping task, pigs’ feet were not lateralized since only a minority of them showed a preference.
9. In this study, pigs with a general right bias for both using the snout and curling the tail showed differences in their personality compared with pigs with a general left bias: they were bolder, more explorative and more sociable.
10. To investigate emotional processing, another study shows that covering the right eye (i.e. reducing visual inputs coming to the left hemisphere) reduces the positive appraisal of pigs for seeing a positive stimulus.
11. Thus, the simple observation of side preferences (for using the snout, curling the tail, seeing) allows to indicate personality or emotions of our pigs. This was the aim of @LateraLiterally ‘s PhD thesis
12. How can you measure pigs’ laterality? For the snout, the pig is trained to open a flap door behind which a chocolate raisin is hidden. After training, a barrier in front of the flap door “forces” the pig to open the flap door with the left or the right side of their snout.
13. For tail curling, one can observe spontaneous tail curling behaviour in the pen. This is what Adrien did and he found similar results as Charlotte, with pretty blue and red pigs. Anyways, it is important to repeat the measurements for each animal and to calculate a proportion
14. Laterality is a widespread phenomenon in the animal kingdom. In humans, first the lateralization of language was officially discovered, in the 19th century. Our language function is lateralized to the left.
15. Only one century later, scientists discovered that non-human animals are lateralized as well. Since then, we know that laterality is common to all vertebrates and is even present in insects!
What about your animals? Are their right- or left-biased ?
15bis. If you want to know more, you can read the articles of @LateraLiterally here

http://doi.org/10.1093/cz/zoy071
https://doi.org/10.1080/1357650X.2017.1410555
https://doi.org/10.1016/j.anbehav.2019.06.021

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