Sheep die after dog chases them on to rail line at Tuddenham St Martin
A farmer said 14 of her ewes were hit by a train and killed after they were chased on to a railway line by a dog.
Becki Spry, who has sheep near Tuddenham St Martin, near Ipswich, said the incident on 29 December was an "unnecessary loss of life".
She has put up signs urging dog owners to keep their pets on a lead around livestock.
Suffolk Police said it was investigating the incident and urged dog owners to be responsible.
Ms Spry said she received a telephone call to say the ewes were on the railway line, and 11 of them were already dead when she got there.
She said another two had to be put down due to injuries sustained and another died later.
"It was clear they had been chased through the electric fence, up the bank and on to the railway line to get away from the dog," she said.
"It was very upsetting for us to see; they are our life, we put a lot of time, hours and care into them to make sure they are as well as they can be."
Sgt Brian Calver, from the rural crime team at Suffolk Police, said: "When are we going to get this message across to people? Dog ownership comes with responsibility."
He said the majority of dog owners using the Fynn Valley area were "decent law-abiding people who are doing the right thing".
However, he said: "People need to understand they are walking a natural predator, they might not be aggressive, they might just want to chase and play, but you can't tell a sheep 'It's fine, that dog just wants to play with you.'
"That is the owner's responsibility and all it takes is to keep the dog on a lead, it's not difficult."
Find BBC News: East of England on Facebook, Instagram and Twitter. If you have a story suggestion email [email protected]