A PACK of nine sheepdogs may have been doped by thieves who stole a quad bike worth £2,200 from a farm.

The dogs normally bark when any stranger calls at Streatlam Grange Farm, at Marwood, near Barnard Castle, County Durham.

But farmer Ted Harrison and his wife, Mandy, did not hear anything while the thieves wheeled the bike away from their yard and took it across two fields in the dark at the weekend.

They are thought to have taken it more than 400 yards to a road before starting its engine and riding it away or loading it on a vehicle.

Mrs Harrison said: "I am convinced they must have done something to silence the dogs. They normally make a great deal of noise if anyone comes near in daytime, and even more at night."

Mrs Harrison, who breeds sheepdogs, said the oldest of the pack, 13-year-old Bill, is particularly good at guarding. He usually barks first and sets off the others - Moss, Sweep, Shep, Roc, Sal, Skye, Bob and Gen.

Gen has had a litter of eight pups, and would be likely to become more agitated than usual if anyone was moving about nearby during the night.

Mrs Harrison said: "I think the intruders must have been able to put some dope in the dogs' food earlier in the day so they would sleep soundly all night. That seems the only explanation."

Mr Harrison discovered the theft when he got up early and went to fetch the quad bike so he could tend his lambing sheep.

The dogs were still quiet the next morning when police arrived to investigate the theft, and one officer said he was surprised at how little they barked.

A police spokesman said it was possible the dogs had been drugged. He also said forensic evidence had been discovered at the scene, and that it was being examined.