Is a pig grunt worth a thousand words? Sixteen researchers from Denmark, Switzerland, France, Germany, Norway, and the Czech Republic conducted a study about pig sounds and their findings were published in Scientific Reports.
Using 7,414 sounds from 411 pigs in different scenarios (from their birth to death), a machine learning algorithm was created to decode if a pig’s sound indicates a positive or negative emotion.
"With this study, we demonstrate that animal sounds provide great insight into their emotions. We also prove that an algorithm can be used to decode and understand the emotions of pigs, which is an important step towards improved animal welfare for livestock", says Associate Professor Elodie Briefer of the University of Copenhagen’s Department of Biology at the University of Copenhagen, who co-led the study.
Researchers created mock scenarios for the pigs to evoke more emotions in the middle of the spectrum — an arena with toys or food and another without any stimuli. Unfamiliar objects were also included for the pigs to interact with them. The pigs’ calls, behavior, and heart rates were monitored and recorded.
The emotions of pigs were defined according to how they react to different positive and negative stimuli. For example, pigs are in a negative emotion if they stand still, produce a lot of vocalizations, and try to escape. Additionally, missed nursing, social isolation, piglet fights, piglet crushing by the mother, castration, and handling and waiting in the slaughterhouse evoke negativity to the pigs. Meanwhile, they are in a positive emotion whenever they explore their surroundings and posture their ears forward, huddle with littermates, get nursed, receive positive conditioning and enrichment, reunite with the mother, and run freely.
Previous research indicates that high-frequency calls (such as screams and squeals) indicate negative emotions and low-frequency calls (such as barks and grunts) happened both in situations where the pigs experienced positive or negative emotions.
"There are clear differences in pig calls when we look at positive and negative situations. In the positive situations, the calls are far shorter, with minor fluctuations in amplitude. Grunts, more specifically, begin high and gradually go lower in frequency. By training an algorithm to recognize these sounds, we can classify 92% of the calls to the correct emotion", explains Elodie Briefer.
Now that an algorithm to decode pig grunts was created, researchers need someone who wants to develop it into an app that farmers can use to effectively understand the emotions of their animals and improve their welfare.
Image credit: Marek Piwnicki and Kenneth Schipper Vera on Unsplash, Elodie Briefer