Pro-active pigs were willing to see whether there was a positive outcome in the mystery bowl.Dr Lisa Collins, from the University of Lincoln, and colleagues wrote: “Reactive pigs in the less enriched environment were more pessimistic and those in the more enriched environment more optimistic.”These results suggest that judgment in non-human animals is similar to humans, incorporating aspects of stable personality traits and more transient mood states”.The researchers wrote in the abstract of the paper that it is the first time cognitive bias has been investigated in non-human animals. Their nature was tested by offering two food bowls at opposite sides of the room, one filled with sugar-coated chocolate sweets and the other filled with disappointing coffee beans.Optimistic pigs were likely to check a third bowl, which was either filled with coffee beans or sweets.Pessimistic pigs would not even bother checking whether it was full of sweets or not.Pigs with less space and straw were more likely to be moody and pessimistic, and less likely to snuffle about for sweets.A bad mood in a pig would mean the animal was more inclined to expect a negative outcome from the bowl; coffee beans instead of sweets. Scientists have found that pigs can be optimists or pessimists, just like humans.In a new study by the University of Lincoln, published in Biology Letters, it was found that some pigs are go-getters, whereas others are moody and see the glass as half-empty.Researchers tested 36 domestic pigs, some of which were given roomy, comfortable living space with extra layers of deep straw. These results suggest that judgment in non-human animals is similar to humans, incorporating aspects of stable personality traits and more transient mood statesDr Lisa Collins Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.