Police said the owner was checking on his herd Monday when he found the dead cow. A veterinarian found the bullet's entry and exit wound during an autopsy.
The loss will cost the owner an estimated $4,000, police said.
Police have notified the ministry of natural resources, the municipality of Northern Bruce Peninsula and the ministry of agriculture of the incident.
Anyone who has information is asked to call police at 1-888-310-1122. People can also leave anonymous tips on Crime Stoppers phone line at 1-800-222-8477 or website www.crimestop-gb.org, where they may be eligible for a cash reward of up to $2,000.