Harold Lee, 75, died when his herd of 100 cows stampeded as he moved them along a B-road with his son, Richard, last August.
His family has claimed the animals were distressed by the emergency lights and sounds of the fire engine which was heading to a nearby emergency.
They believe the accident might have been avoided had the fire crew waited until the cows were safely herded off the road before proceeding.
Harold Lee was at the rear of the herd when the Holstein Friesian cows crushed him.
He was airlifted to Royal United Hospital, Bath, Somerset, before being transferred to Frenchay Hospital, Bristol. He suffered severe head and chest injuries and died six days later.
Police began an investigation and have arrested a 29-year-old fireman on suspicion of manslaughter by negligence.
The unnamed man, a member of the engine crew, has been bailed until Friday.
Mr Lee's elder son, Andrew, 47, who works at the family’s farm in Burtle, Somerset, has claimed the accident could have been avoided had the fire crew waited for a few minutes as the cows were safely herded off the road.
He said: "We have always said this incident should not have happened. My brother Richard said he tried to stop the engine coming through.
"He said a fire engine had frightened the cows and father was hurt.
"My father had been doing this for 50 years and there has never been a problem before.
"As a family we would like justice to help put this behind us as quickly as possible.
"Things are pretty raw at the moment and will be until we get some answers as to why he died.
"He was a family man and a community man, that was his life and he loved it.
"Hopefully this can be a step forward to justice for him."
A Devon and Somerset Fire spokesman declined to comment about the arrest but has said the crew was on its way to a road accident
Cows 'spooked' by fire engine trample farmer to death - Telegraph