YOU can't get much happier than a pig in muck – but they can be unhappy too, according to new research.

Experts say the animals are just as likely as humans to feel the glass is half empty or half full, depending on their living conditions.

Farmers in Gloucestershire say they agree with the report from Newcastle University's School of Agriculture, Food and Rural Development.

James Hart, who runs a pig farm near Cirencester, said: "I think it is definitely a good idea and it is something we have all been looking at over the years because we realise that our pigs are intelligent animals.

"By law we have to have enrichment tools in their pens, like wooden blocks, bits of chain and all sorts of things and it definitely makes them happier.

"We want happy pigs because then they grow better, which is better for us. A happy pig is a healthy pig."

Simon Righton, from Old Farm, Dorn, near Moreton-in-Marsh, keeps more than 100 pigs and agrees pigs can feel optimistic or pessimistic according to how they are being treated.

During the World Cup, Mr Righton's pigs enjoyed a game of football. He said: "They all have good things to play with to keep them happy."

During the study, led by Dr Catherine Douglas, the team employed a technique to "ask" pigs if they were feeling optimistic or pessimistic about life as a result of the way in which they live.

Pigs were taught to associate one sound with a treat, and another with something unpleasant. Then they placed half the pigs in an enriched environment – with more space, freedom to roam in straw and play with toys – while the other half were placed in a smaller, boring environment with no straw and only one non-interactive toy.

The team then played an ambiguous noise – a squeak – and studied how the pigs responded.

Dr Douglas said: "We found that almost without exception, the pigs in the enriched environment were optimistic about what this new noise could mean and approached expecting to get the treat," she said.

"In contrast, the pigs in the boring environment were pessimistic about this new strange noise and, fearing it might be mildly unpleasant, did not approach for a treat.

"It's a response we see all the time in humans where how we are feeling affects our judgment of ambiguous events."