The Romney cross lambs were taken in two lots from a flock of more than 260 on his 22ha property, the man, who declined to be named, said.
"They were ready to go off to the works and whoever took them selected the best lambs - the biggest ones.
"There's too many for a freezer so they must have been sold or passed on to other people, so somebody out there must have heard about cheap lamb being available just around Christmas time or shortly afterwards."
He had counted the stock when shifting the mob before Christmas and noticed that 18 were missing.
A week later, he counted the mob again and a further 10 were gone.
The farmer has reported the theft to the police and Central Otago sub-area commander Senior Sergeant Jill Woods said investigations were continuing.
Snr Sgt Woods said it appeared to be an isolated incident but police would like to hear from anyone else who believed stock had been taken from their property.
Police would also like to hear from anyone who had witnessed suspicious activity around farm properties, especially in paddocks close to roads.
The farmer said his land was next to a road and the theft was possibly carried out during moonlit nights.
He thought the stock may have been shot on the property as two of the remaining stock had injuries which could have been gunshot wounds.
"It seems to have been a well-organised operation so you have to wonder if they were stolen to order."
Other farmers in the area should check their stock numbers, he said.
If anyone had been offered lamb at a price "too good to be true", they should contact the police, he said.
