The study involved 72 male and female juvenile pigs. Half were housed in spacious ‘enriched’ pens with straw bedding, while the other half were kept in more compact ‘barren’ pens with partially slatted concrete floors, which adhered to UK welfare requirements.

Tests were conducted to see how the pigs responded to social isolation and new objects, and to see whether their responses were consistent across two tests (defining their 'personality').

The study indicated that pigs with more proactive personality types produced grunts at a higher rate than the more reactive animals. It also found that male pigs (but not females) kept in the lower-quality conditions made fewer grunts compared with those housed in the enriched environment, suggesting greater susceptibility among male pigs to environmental factors.

The results add to evidence that acoustic signalling indicates personality in pigs, and suggest personality needs to be kept in mind when using vocalisation as a measure of the animals’ welfare status.

Mary Friel, lead author of the study and PhD student at Queen’s University Belfast, added: “The aim of this research was to investigate what factors affect vocalisations in pigs so that we can better understand what information they convey.

"Understanding how the vocalisations of pigs’ relate to their personality will also help animal behaviourists and welfare experts have a clearer picture of the impact those personalities have on communication, and thus its role in the evolution of social behaviour and group dynamics in social species."