AN independent cattle expert has told an inquest that a herd of 30 cows which trampled to death a university professor may have wanted to "eliminate" him.

Andrew Marshall said there was a high risk of attack as the breed of cows which rounded on Mike Porter were "unpredictable", "more excitable" and "less calm".

When threatened, the cows - a continental breed - trigger a "fight or flight" response, and in the worst possible scenario they seek to "eliminate" threats, he said.

Mr Porter, 66, was walking with his brother John and his two dogs when they were encircled by the herd and stamped on halfway across a field in Turleigh, Wiltshire.

Mr Porter, who had just retired from his post at Edinburgh University, managed to scramble out of the field but collapsed and died shortly afterwards. A hoof mark was found on his chest.

The attack happened on Timothy Rise Farm on May 13, 2013 in an area where three previous cow attacks had injured members of the public, Salisbury Coroner's Court heard.

Mr Marshall - an independent agricultural expert since 1985 who has previously consulted for the government - said farmer Brian Godwin and his family farmed beef cattle and raised them as "suckler cattle" - where the livestock wean their own calves and have little human interaction.

Mr Marshall, who visited the farm with HSE inspectors and police, said: "A farmer who puts suckler cows in a field with a footpath is aware there is a high risk of attack to the public.

"Farmers are very careful. As soon as you got suckler cows on a farm you have to be very careful.

"If those animals had been involved in previous incidents then these animals are not frightened of humans and if they perceive them entering their comfort zone they are confident enough in dealing with it."

He said of the previous incidents: "Previously the cattle attacked but then left the individual as they had dealt with it. But in this instance they pursued the Porter brothers as they left the field. This time they were going to deal with this threat and they had to be eliminated."

The inspector from the Health and Safety Executive said their records only had one reported attack as the others went unreported.

Dawn Lawrence said they wrote to the farm about the need for additional safety measures after one incident in October 2011.

The Godwins subsequently installed signs saying: "Cows and calves in field."