BERLIN (AP) — Police in western Germany are appealing for help in cracking a potentially very cold case.

Authorities say about 60 containers of bull sperm were stolen from a farm in the town of Olfen, 90 kilometers (56 miles) northeast of Cologne, late Monday or early Tuesday.

Police said in a statement Wednesday that while it's unclear how the rustle happened, the precious cargo needs to be supercooled with liquid nitrogen at –196 Celsius degrees (–320 Fahrenheit) so it isn't spoiled.

They are seeking tips from the public that might lead to the recovery of the sperm, which was intended for artificial insemination.