Farm owner Gilbert Crawford, internationally known through his pedigree Charolais cattle, said he believed the attack – which happened early yesterday – was carried out “with a hatchet or some sort of sharp instrument”.

Speaking yesterday as a clean-up was being carried out on his farm, Mr Crawford said in the latest attack a cattle trailer, a forklift and a feeder were damaged.

“As yet I am not sure how much money it will take to get them fixed or if it is even worth it,” he said.

“I think this happened because whoever did it knew I was planning on going to the Balmoral Show on Tuesday.

“I am still planning to go to show the Charlois cattle but I have kind of lost heart after this.

Mr Crawford added: “This is the fourth attack. Everyone knows who is carrying out these attacks but the police cannot get him.

“I first saw the damage when I came out of the house this morning, but you can’t sit up all night worrying about what is going to happen next.”

Last night a police spokesman said: “Police are investigating damage caused to farm machinery at a property on the Tamnymartin Road in Maghera.

“Gates, a cattle trailer and a forklift were among the items damaged during the incident, which is believed to have occurred sometime during Monday night.

“Anyone with information regarding the incident is asked to contact police on 0845 600 8000.

“A police investigation into this and previous related incidents is continuing and we are following up on a number of lines of inquiry.”

Last month 30 jumbo fertiliser bags were slashed and animal feed bins opened and the contents strewn across the yard and contaminated.

Farm buildings were broken into and serious damage caused in January.

As well as the damage, thousands of pounds worth of equipment and produce was also stolen over the same period and into last year.

There was also concern about environmental damage as pipelines to two diesel tanks were cut, causing 10,000 litres of fuel to flow into a neighbouring field, polluting it.

Earlier Mr Crawford’s son Jonathan said the family was upset at the damage as it was just such a waste.

He said they had strong suspicions about who was behind the “vendetta”.