Dorset police are appealing for witnesses after 160 sheep were stolen from a field near the village of Wool.
The rustlers are thought to have had to use a large lorry to move the animals, which were all marked and electronically tagged.
Police said the incident took place between 8am on Saturday 2 November and 2.30pm on Monday, at the field which lies next to the A352 between Wool and the nearby village of East Stoke.
Police Constable Adam Taylor, of Wareham police, said: “The thieves would have needed a good understanding of livestock and used a large vehicle, possibly a six or eight wheeler type lorry, to move the sheep.
“I am appealing to witnesses and anyone who may have seen any unusual activity in the area around this time.
“All the sheep had colour markings and were electronically tagged. If anyone has been offered sheep in unusual circumstances or for very low prices please contact the police on 101.”
No arrests have been made.