Portland detectives are investigating the theft of 22 genetically significant Suffolk stud sheep, from a property south-west of the city.
The 21 ewe lambs and a ram, valued at $21,000, were stolen from Henty stud Updown Park's Portland lease block, Bridgewater Road, some time in the last fortnight.
Updown Park's Daniel Lutz said he discovered the theft on Sunday, when he went down to the block to drench the sheep running there.
"I had them on the lease block, down at Portland, because it's very dry up here - being on the coast they had some very good feed.
"Because I am joining them, I had them on good paddocks."
The ewes had a high percentage of United Kingdom blood, "they are obviously irreplaceable, because of the biosecurity rules that mean you can't really bring any more of those genetics in to the country".
Mr Lutz said he had acquired the bloodlines from Advanced Performance Suffolks (APS) stud, which dispersed in April 2021.
He bought bought nine ewes and seven ewe lambs at an average of $700 and to a top of $1950 at the dispersal.
"It's a bit of a disaster, really," he said.
"They (the sheep) were all born in Australia, through the work of APS."
He said he didn't hold out much hope of getting the sheep back.
It was the first year he had decided to use the ram, which had strong UK genetics.
"Hopefully some of the ewes that are still there are in lamb to him," he said.
"It's not so much the dollar value, it's the genetic value - they are genetics that you can't just ring up another stud and buy.
"The fact someone would come and steal them is pretty devastating.
"If they were commercial sheep, it's still terrible, but I'll never be able to get these genetics back."
Mr Lutz said when he went to get the sheep in for treatment, "they were just gone".
"I couldn't see the ram and there didn't seem to be enough sheep -when I got them in I counted them in I discovered the loss."
He said he believed the theft was recent, as he had people checking on the flock every day.
"I'd seen them a fortnight before and I'd counted them myself, and they were definitely there," he said.
The ewe lambs were born between 2020-2022 - "they were mainly maidens," he said.
"They were out with a very high indexing ram," he said.
He appealed to anyone who might be offered the sheep for sale to notify police.
Sheep theft was too common, and needed to be publicised more, he said
A spokeswoman for Portland detectives said no signs of forced entry or damage to gates or fences had been reported.
There were tyre tracks from a vehicle that didn't belong to Mr Lutz near the property, the spokeswoman said.
Anyone with information can call Crimestoppers on 1800 333 000 or Portland police, 5522 1500.