A new study seeks to answer a key question: what does it mean when a pig oinks, squeals or grunts?
In the study published earlier this month, researchers from the University of Copenhagen, ETH Zurich and the French National Research Institute for Agriculture, Food and Environment recorded 7,414 sounds from 411 pigs in different scenarios.
The researchers then developed an algorithm to decode whether pigs were experiencing a positive emotion, negative emotion or something in between.
The recordings were collected in situations encountered by commercial pigs from birth to death, the University of Copenhagen said. Researchers also monitored behavior and heart rates.
“Due to the impact of emotions on vocalization, the analysis of vocal expression of emotions is increasingly being considered as an important non-invasive tool to assess the affective aspects of animal welfare,” the study said.
It added: “In the last decade, it has been shown that vocalizations of various animal species produced in specific emotional contexts and/or physiological states display specific acoustic characteristics.”
Positive situations include when piglets suckle from their mothers or when they are reunited with family members. Negative situations include separation, fights, castration and slaughter.
Researchers also developed mock scenarios designed to evoke more nuanced emotions. Such scenarios included an arena holding toys or food and a corresponding arena without any such stimuli. They also introduced new and unfamiliar objects.
The study revealed that pigs typically vocalize high-frequency calls such as screams or squeals in negative situations, while low-frequency calls such as barks and grunts occur when pigs experience both positive and negative emotions.
“There are clear differences in pig calls when we look at positive and negative situations,” said Elodie Briefer, a professor at the University of Copenhagen’s biology department who co-led the study.
“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.”
According to the researchers, most modern animal welfare efforts focus on physical health.
Briefer said: “We need someone who wants to develop the algorithm into an app that farmers can use to improve the welfare of their animals” including their emotions.
