PARENTS and animal-lovers have been warned to be on their guard, amid fears that a cruel killer has been leaving arsenic on York's Knavesmire.

One dog died only an hour after eating some bread left on a path near York Racecourse, and other pets have also become severely ill within minutes of eating items found on the field or in Knavesmire Wood.

Police are now investigating and the public have been warned to be alert to the potentially-fatal dangers. The Dogs Trust also voiced disgust.

Vet Lesley Edwards, who fought to save the dog that died, said the poison was stronger than any they were used to. She said: "If it's that violent and serious to a dog, then I think it could well be dangerous to a child."

She said the dog that had died, a four-year-old bearded collie called Summer, exhibited all the symptoms of arsenic poisoning: pain, weakness, salivating and diarrhoea, before collapsing and dying.

Summer died on Saturday, after eating bread while out walking with her owner, Denise Barley, and four other bearded collies.

Ms Barley said she initially thought the bread had been left out for birds, and thought nothing of it until Summer became ill.

She died less than an hour later at Abbeyfield Vets, in Clarence Street.

Ms Barley said: "She went back in the car and it was when I was in traffic going back into York that she got ill. From the dog eating the bread to the vet was about 45 minutes to an hour, and it was too late by then.

"It was a horrible way to die, the poor dog. She would have been in pain and her muscles were going into paralysis."

Ms Barley, who comes from Inverness-shire and was visiting a friend in York, said it could have been far worse if a child had been there. She said: "It could so easily have been picked up by a toddler."

Mrs Edwards, practice principal at Abbeyfield, said: "Arsenic is found in pesticides, but if it was found on bread, that does suggest it was deliberate."

Dog-walker Penny Lee, 59, of South Bank, said her black Labrador, Bob, fell ill after eating something in Knavesmire Wood.

She said: "Within two minutes his back legs were going and thick yellow stuff was coming from his mouth and he got diarrhoea. I took him to the vet's. If he had been a smaller dog, he might have died, but he's back to normal now."

She added: "It is not only dogs at stake - children play in that wood too."

Local councillor Sandy Fraser said: "Clearly we are concerned if this is a deliberate attempt to poison dogs and, of course, it is not just dogs at stake."

York Racecourse's marketing manager James Brennan, who often walks his dog, Charlie, on Knavesmire, said: "A number of us have dogs and are dog-walkers on Knavesmire and as a part of the community of York and South Bank, this is both sad and disturbing."

Local police sergeant Ann Brannan said they had been notified of Saturday's case only, and urged anyone else who knew of other incidents to notify police.

If people found what they believed to be poison, they should notify City of York Council or the police to try to get a sample, and should be careful handling anything themselves.

A City of York Council spokesperson said: "It is not clear what caused the dog (Summer) to become ill and whether the bread it ate was indeed contaminated with some sort of poison.

"We would urge dog owners to be on their guard; keep an eye out for anything unusual; and try to stop their pets from eating anything that they pick up on a walk."