An elderly farmer has said he has been left "sickened" after a flock of pregnant ewes was stolen.
The sheep were taken from a field near the village of Park, Co Londonderry, sometime between 10:00 on 7 February and 10:30 the following day.
Seamus Gormley, 76, told BBC Radio Foyle he could not believe people could be "low enough" to steal his flock.
Officers are working to establish if this incident is linked to the theft of 50 lambs near the area last month.
Mr Gormley said he received a phone call from a farm worker that 13 Suffolk/Texel-cross pregnant ewes were missing from a flock of 30.
The pensioner said he initially believed some of the flock had simply escaped the field and refused to believe that they could have been stolen.
He said that, after painstakingly searching nearby fields, his daughter then called the police three days after noticing that they had gone missing.
'I didn't sleep last night'
"It's not even just the financial loss, but it's that people are low enough to do this and I want to get them caught," he said.
"They were top class ewes, they were the best ones I had, so you could be talking a couple of thousand pounds.
"It is hitting me worse now than it did in the first few days ... I didn't sleep last night. I am an old age pensioner and I don't need that carry on."
Police have asked anyone who saw any unfamiliar vehicles in the area of the junction of Kilcreen Road and Altinure Road between 7 and 8 February to come forward.
Inquiries are also ongoing into the theft of the flock of 50 lambs on 25 January, police said.
"The removal of these ewes would have required planning and the use of a vehicle, for example a trailer, to transport the animals away from the area," Sgt Johnston said.
"Not only is there the value of the ewes and the lambs, but there is also the cost involved in rearing and farming the animals."
Sgt Johnston said officers were working to establish if that incident was linked with the theft on Kilcreen Road.
Farmers in the area are being asked to take a number of security steps including padlocking field gates, checking stock regularly and varying times of feeding.