The Chin Ball Marker is an effective heat detection aid for cattle. A rugged nylon strap and heavy buckle hold the polyvinyl harness underneath the chin of a penectomized bull. The stainless steel ball inside the reservoir works on the same principle as a ball point pen. The coloured ink on the female's back will give a clear indication of which cow is in heat. Ink is sold separately. Ink available in red, blue and yellow.