Thieves have stolen more than 100 Suffolk-cross lambs worth about £9,000 from a farm in County Durham.
Durham Police believe the theft of 136 lambs from Broom House Farm, near Witton Gilbert, took place some time in the early hours of Thursday 7 August.
But a police spokesman said the crime could have been committed earlier in the week because farm staff only realised the sheep were missing when they came to move the animals ahead of a sale.
The lambs were running in a flock of 275 in a field about a mile from the main farm holding.
Farm owner Mark Gray told a regional newspaper that he had never had any sheep stolen in 28 years in farming. Mr Gray put the value of the lambs at about £70 a head, making the total loss £9,520.
Police have asked anyone with information to call 101, quoting the crime reference number DHM-07082014-0141 or to call Crimestoppers anonymously on 0800 555 111.
The lamb theft came as the NFU Mutual Rural Crime Survey, released on 11 August, identified rustling as a growing problem particularly in the north of England and Northern Ireland.
The cost of livestock theft rose 25% across the UK, making 2013 one of the worst years on record, the survey showed.
Northern Ireland, which is currently suffering a spate of cattle and sheep rustling, was the most seriously affected part of the UK.
Large-scale sheep rustling in the north-west and north-east of England led to theft claims increases of 68% and 52%, respectively.
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