Babe may be the most famous sensitive pig in the world but new research from Newcastle University suggests he is by no means the only one.

Experts from the university's School of Agriculture, Food and Rural Development have shown for the first time that a pig's mood mirrors how content he is, highlighting that pigs are capable of complex emotions which are directly influenced by the environment in which they live.

Led by Dr Catherine Douglas, the team has employed a technique to 'ask' pigs if they are feeling optimistic or pessimistic about life as a result of the way in which they live.

In an experiment reminiscent of Pavlov's dogs, the Newcastle team taught the pigs to associate a note on a glockenspiel with a treat – an apple – and a dog training 'clicker' with something unpleasant – in this case rustling a plastic bag.

The next step was to place half the pigs in an enriched environment – more space, freedom to roam in straw and play with 'pig' toys – while the other half were placed in a smaller, boring environment without straw and with only one non-interactive toy.

The team then played an ambiguous noise – a squeak – and studied how the pigs responded. Dr Douglas said the results were compelling.

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

"It's a response we see all the time in humans where how we are feeling affects our judgement of ambiguous events. For example, if you're having a bad day – feeling stressed and low – and you're presented with an ambiguous cue such as your boss calling you into their office, the first thing that goes through your head is what have I done wrong? We call this a negative cognitive bias. But on a good day you greet the same ambiguous event far more positively, you might strut in expecting a slap on the back and a pay rise.

"This 'glass half empty versus glass half full' interpretation of life reflects our complex emotional states, and our study shows that we can get the same information from pigs. We can use this technique to finally answer important questions about animal welfare in relation to a range of farm environments, for pigs and potentially other farm animals."

The research, funded by Universities Federation for Animal Welfare (UFAW) was presented at the organisation's annual conference in York.

Quality of life of our farm animals is becoming increasingly important to consumers, scientists and government and the study is part of ongoing research at Newcastle to further our understanding of animal welfare and improve the lives of farmed stock.

Sandra Edwards, professor of agriculture at Newcastle University and one of the UK's leading experts in pig welfare, said the next step would be to refine and further validate the methodology so it could be used to help scientists determine what is really important to the pig for its well-being.

She explained: "Historically, animal welfare research looked only at alleviating suffering. Now the UK industry itself is going beyond a minimum standard and funding research to explore measuring, and then promoting, quality of life.

"Although techniques exist to measure stress, in the past we haven't been able to directly ask a pig if it is happy or not. Instead we have assessed production systems based purely on human perceptions and our best interpretations of behaviour.

"Our research, for the first time, provides an insight into pigs' subjective emotional state and this will help scientists and farmers to continue to improve the lives of their pigs in the future."

Dr Douglas said that in their experiments they deliberately used only environments that could be easily and sustainably introduced in commercial systems.

She added: "UK farmers have some very difficult decisions to make in order to compete in the global market and to suggest that we make all pig farms free-range is simply not practical, possible or necessarily desirable. Unfortunately, consumers buying cheap imports have the biggest impact on animal welfare and this puts pressure on UK farmers who, as a rule, do their utmost to ensure good welfare of the UK pig herd.

"In our experiments, the enriched environment was also a widespread commercial housing system, so a 'happy pigs' system already exists on many farms across the UK."