The calves were taken from their mothers overnight on Tuesday to Wednesday, July 26-27 from a roadside paddock at an Ermedale dairy farm.
"I'm hopeful this is a one-off incident," says Senior Constable Kelvin Templeton.
"However, farmers and their workers and neighbours need to be really vigilant, and prepared to call Police straight away on 111 if they are witness to this activity or anything they believe is suspicious."
Anyone with information about the theft is asked to contact Riverton Police on 03 234 7070, or call CrimeStoppers, anonymously, on 0800 555 111.
