Ulster's pigs compete in a popularity contest that's as tough as any American high school, new research has revealed.
Dairy cows and pigs at a research centre in Hillsborough, Co Down, form close friendships just as humans do - and newcomers can be ostracised to the extent that they lose out on food and places to lie down.
The friendships of farm animals have been laid bare in new research carried out by Dr Niamh McConnell at the Agri-Food and Biosciences Institute (AFBI) in Hillsborough, in conjunction with the School of Psychology at Queen's University, Belfast.
Modern farming practice can cause social upheaval within the groups of animals, so the research may help discover how to minimise stress. Dr McConnell said: "I'm particularly interested in how animals relate to each other. Under natural conditions, animals live in stable groups and, with farming practices, that is not always possible."
She studied the herd of finishing pigs at the centre, discovering that the animals formed firm friendships within the group.
"What was interesting was that some seemed to be more popular than others - some had a number of friendships; others didn't," she said.
"This may explain why routine farming practices associated with splitting and reforming groups have greater impacts on some animals than others."
Her observations revealed that some of these friendships were short-term and fickle, while others were longer-term stable relationships.
Meanwhile, studies of the centre's sows and Friesian dairy cattle revealed that young animals being added to an established group don't integrate well.
"Sometimes they have difficulties getting access to lying areas and food," Dr McConnell said.
"But they form very strong bonds with the animals they are added in with."
McConnell advised that when animals are added to groups, it should be in pairs or small sub groups, so that they can thrive.