ONCE they were a byword for mindless docility. But cows have a secret mental life in which they bear grudges, nurture friendships and become excited over intellectual challenges, scientists have found.

Cows are also capable of feeling strong emotions such as pain, fear and even anxiety — they worry about the future. But if farmers provide the right conditions, they can also feel great happiness.

The findings have emerged from studies of farm animals that have found similar traits in pigs, goats, chickens and other livestock. They suggest that such animals may be so emotionally similar to humans that welfare laws need to be rethought.

Christine Nicol, professor of animal welfare at Bristol University, said even chickens may have to be treated as individuals with needs and problems.

“Remarkable cognitive abilities and cultural innovations have been revealed,” she said. “Our challenge is to teach others that every animal we intend to eat or use is a complex individual, and to adjust our farming culture accordingly.”

Nicol will be presenting her findings to a scientific conference to be held in London next month by Compassion in World Farming, the animal welfare lobby group.

John Webster, professor of animal husbandry at Bristol, has just published a book on the topic, Animal Welfare: Limping Towards Eden. “People have assumed that intelligence is linked to the ability to suffer and that because animals have smaller brains they suffer less than humans. That is a pathetic piece of logic,” he said.

Webster and his colleagues have documented how cows within a herd form smaller friendship groups of between two and four animals with whom they spend most of their time, often grooming and licking each other. They will also dislike other cows and can bear grudges for months or years.

Dairy cow herds can also be intensely sexual. Webster describes how the cows become excited when one of the herd comes into heat and start trying to mount her. “Cows look calm, but really they are gay nymphomaniacs,” he said.

Donald Broom, professor of animal welfare at Cambridge University, who is presenting other research at the conference, will describe how cows can also become excited by solving intellectual challenges.

In one study, researchers challenged the animals with a task where they had to find how to open a door to get some food. An electroencephalograph was used to measure their brainwaves.

“Their brainwaves showed their excitement; their heartbeat went up and some even jumped into the air. We called it their Eureka moment,” said Broom.

The assumption that farm animals cannot suffer from conditions that would be considered intolerable for humans is partly based on the idea that they are less intelligent than people and have no “sense of self”.

Increasingly, however, research reveals this to be untrue. Keith Kendrick, professor of neurobiology at the Babraham Institute in Cambridge, has found that even sheep are far more complex than realised and can remember 50 ovine faces — even in profile. They can recognise another sheep after a year apart.

Kendrick has also described how sheep can form strong affections for particular humans, becoming depressed by long separations and greeting them enthusiastically even after three years.

The Compassion in World Farming conference will be opened with a keynote speech by Jane Goodall, the primatologist who founded the study of animal sentience with her research into chimpanzees in the early 1960s.

Goodall overturned the then accepted belief that animals were simply automatons showing little individuality or emotions. It has taken many years, however, for scientists to accept that such ideas could be applied to a wide range of other animals.

“Sentient animals have the capacity to experience pleasure and are motivated to seek it,” said Webster. “You only have to watch how cows and lambs both seek and enjoy pleasure when they lie with their heads raised to the sun on a perfect English summer’s day. Just like humans.”