Police said 585 head of sheep were stolen from a property on Sunraysia Highway, Lexton in Victoria between July 23 and September 19.

The mixed-sex merinos were 12-months-old, police said.

Another 16 merino rams were allegedly stolen from the same farm between November 4 and November 6.

Farm crime inspector Paul Hargreaves said "this theft is concerning and unique as it involves a significant quantity of sheep and breeding rams of stud quality".

"Farm crime strikes at the very heart of a farmer's livelihood, resulting in hardships that extend far beyond monetary losses," he said.

The Lexton farmer notified police as soon as the sheep were noticed missing, investigators said.

Police suspect the culprit needed to use a livestock truck to get away with their wooly heist.

Though investigators said multiple trips could have been made using a stock trailer.

"Every piece of information matters greatly in solving crimes," Inspector Hargreaves said.

"Whether you witness something, overhear something, possess knowledge, or even harbor suspicions related to sheep theft, please don't hesitate to report it immediately."

"By promptly reporting anything unusual to the authorities, you could be the vital link in solving crime."

If you're the victim of livestock theft, contact your local police station or the Police Assistance Line on 131 444. Phone 000 for immediate assistance.

Anyone in the farming community who notices suspicious activity, no matter how small, is encouraged to contact their local police station immediately or make an anonymous report to Crime Stoppers Victoria on 1800 333 000 or via http://www.crimestoppersvic.com.au/