Animal welfare: a translator to decode the emotions of pigs through their growls

In his book “ The expression of emotions in humans and animals ”, Darwin describes many species using sounds to convey their emotions. He insists on the fact that animals that are usually not very talkative, such as rabbits, produce shrill cries when they are in pain. He explains that many also vocalize in situations of well-being, when they find a lost companion for example.

Animal emotions, defined as Intense, short-term reactions to specific events have attracted increasing interest in recent decades, not least because of growing concern for animal welfare. But what are the acoustic markers of these emotions, how are they coded? In order to answer these questions, a team of international researchers focused on domestic pigs. Their results are published in the journal Scientific Reports.

Recognizing the presence of emotions in animals: starting point

Just like humans, animals experience fear of novelty and frustration when the situation does not meet their expectations. They are reassured by predictable events and enjoy being in control of their environment. The knowledge acquired on the mother-young relationship and, more generally, on social ties, as well as the demonstration of their cognitive abilities, also contribute to bringing animals closer to humans. Neurobiology, for its part, shows that in mammals, similar cerebral structures are involved in different emotional behaviors.

Alain Boissy, director of research at INRA-Clermont-Ferrand-Theix and co-author of the analysis, declares: “Even if it is still difficult to have operational indicators of their mental state, we have made considerable progress in the objectification of the emotions of animals ”. These advances have been made concrete by the European program Welfare Quality, which has established in 2000 a European standard for the assessment of animal welfare. It includes measurements on the animal, its health and its behavior, in addition to measurements on the breeding conditions.

It should be noted that the research at the animal confirms that emotions are not automatic and reflexive processes, but rather can be explained by elementary cognitive processes. This line of thought suggests that an emotion is triggered by an individual’s assessment of their environmental situation. This is the case of domestic pigs displaying very sophisticated varieties of vocal expression.

In fact, previous studies have established correlations between high-frequency calls, such as screams, associated with negative emotions, and low-frequency growls associated with positive or neutral emotions. Elodie Briefer, professor at the University of Copenhagen, and co-author of the study specifies, in a press release: “An emotion can be described by two main dimensions: its valence (positive or negative) and its level of intensity ”. But between these two extremes lies an assortment of less well-understood sounds. Indeed, coding the emotions in his vocalizations is one thing. Being able to “decode” them when we hear acoustic signals is another.

Varied situations, contrasting emotions, modulated sounds

For this purpose, the researchers recorded pig sounds in various scenarios, associated with positive and negative emotion. Positive situations included for example those where the piglets are suckling their mothers or when they are reunited after being separated. Emotionally negative situations included, among others, separation, fights between piglets, castration and slaughter. Through experimental parks, the researchers also designed in-between situations to evoke more nuanced emotions. These included an arena with toys or food and a similar arena without any stimulus. In addition, pig calls, behavior and heart rates were monitored and recorded where possible.