VETS are urging dog owners to keep their pets on leads when walking near sheep as lambing season approaches.

As heavily pregnant ewes prepare to give birth, they become more vulnerable, and vets say they have seen in increase in the number of sheep attacking dogs, sometimes resulting in lambs being lost and livestock being killed or injured.

Fiona Lovatt, president of the Sheep Veterinary Society, who has worked with sheep farmers in County Durham, said: “I think most owners are well meaning but if your dog is off the lead you may not even be aware of the chasing or attack.

“It is important to know where your dog is at all times as they can cause a lot of damage in a short time.

“At this time of year a dog attack can have drastic effects even for the ewes who are not injured, as the stress may cause them to abort.”

Robin Hargreaves, president of the British Veterinary Association, added: “Even dogs who are usually calm and good natured can become very excitable and difficult to control when faced with livestock."