Newborn lambs were left to die by thugs who separated them from their mothers.
Farmer John Carr found the bodies when he started work in the morning at Balsdean Farm in Rottingdean.
He said: "This is sick and mindless - just why they did it is a complete mystery."
Sheep are normally protective and can put up a fight when their lambs are taken away but Mr Carr found his had been torn from their mothers and taken into a separate field.
They were separated from their mothers and left bleating overnight when they needed constant feeding.
Mr Carr found three of them had died, probably from starvation, and he quickly reunited about a dozen more with their mothers.
Mr Carr, currently lambing 1,800 ewes, said: "If these people believe they are making a point or doing some sort of good then they have got it seriously wrong."
Earlier this week Mr Carr had problems with a dog walker who let his pet into a field where sheep were grazing.
He said: "It is difficult running a farm close to residential areas. Some people have little idea about countryside rules. What lies behind this latest incident, I have no idea."
Police are appealing for witnesses. If you can help call Detective Sergeant Waters on 0845 6070 999.
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