More than 100 sheep have died in what has been described as the UK's worst case of sheep-worrying in living memory.
Farmer Gordon Wyeth discovered a total of 116 sheep, worth about £17,000, at the West Dean Estate near Chichester, West Sussex.
The sheep, many of them pregnant, had been herded into a tight group against a fence and gate bordering woodland, and either died from shock or by being crushed in the flock.
Sergeant Tom Carter, of Sussex Police, said he was "all but 100% certain" that the deaths were caused by dogs as he appealed for information following Monday afternoon's discovery.
Sgt Carter said: "I have never seen or heard of sheep-worrying on this scale before and this was a terrible sight.
"While there are no signs of any of the animals being savaged, we are all but 100 per cent certain that their deaths were brought about by dogs.
"The flock was last checked around lunchtime on Sunday, so the incident could have occurred at any time over the next 24 hours.
"However, if as we suspect it was a dog attack, it may well have happened in daylight and we want to hear from anyone with information about it."
James Osman, the National Farmers' Union adviser for Sussex, said: "This is the worst incident of its kind in living memory and, talking to colleagues around the country, the number of deaths is double what we have come across in the past.
"We are in full support of the police's efforts to discover whose dog or dogs were responsible and urge anyone with information to get in touch with them."
Police said there had been a rise in sheep-worrying and urged dog owners to keep their pets on leads in rural areas. A farmer can legally shoot a dog chasing their livestock and seek compensation from the animal's owner.
Sgt Carter said: "So often in these incidents the owners are horrified by what their dogs have done, but they have to accept that even the most docile of pets can quickly turn into a killer given the opportunity."