Dog owners are being called upon to keep their pets on leads near sheep after one was brutally killed and two others were left injured at Landport Bottom Nature Reserve in Lewes.
Witnesses to the attack, which happened on December 3 or early the following morning, are urged to contact the police.
The dead sheep had its throat ripped out, with bite marks confirming it was a dog attack.
Lewes District Council had installed signs in the area to let people know that sheep were grazing in the field and that dogs should be kept on leads - the council's Neighbourhood First team is also increasing patrols in the area.
The site's shepherd, Charlotte Streeter, said: "I am so upset by the amount of sheep worrying and attacks we have had this year. If dog owners could just read the signage provided and keep dogs on leads around the livestock as it is totally gutting seeing an animal you have cared for since it was born be brutally attacked and killed."
This year has seen the most dog attacks at the council-owned Landport Bottom site since the signs were introduced 12 years ago.
Councillor Julie Carr, Cabinet Member for Recycling, Waste and Open Spaces, said: "This was a horrific attack and dog owners must stop this happening.
"Due to Covid-19 restrictions, many more people have been exploring their local countryside which is a great thing but has brought problems too. Dogs have sometimes been allowed to roam free in areas where they should be kept on a lead, with owners not necessarily realising the risk of harm to farm animals.
"It is important to realise that even well-behaved dogs may need to be kept on a lead for all or parts of walks in the countryside to keep livestock and wildlife safe.
"Sheep are natural prey to dogs, who will chase them. Some of the sheep at Landport Bottom and in other parts of the Downs are pregnant at this time of year and the stress of being chased can cause them to abort their lambs.
"Allowing a dog to chase a sheep, never mind kill it, is illegal. If anyone sees this happening anywhere in our countryside, they should report it to the police."
Councillor Matthew Bird, Cabinet Member for Sustainability, said: "As a local resident, I know how much Landport Bottom is valued and how saddened residents are at this wholly preventable attack.
"Dog owners should obey signs at all times to prevent any more unnecessary sheep deaths. It is really important that Landport Bottom is grazed because the sheep are restoring the area to flower-rich chalk grassland, making this a rare habitat not only for the UK, but also globally."