The marker fits under the chin of the teaser (Gomer) bull. The stainless steel ball bearing, working on the same proven principle as the ball-point pen, marks cows in heat with a specially formulated, nontoxic marking fluid that adheres to the ball and resists drying. The adjustable leather harness holds the reservoir securely under the bull's chin. The fluid reservoir holds a sufficient supply for 25-30 mountings. It is easily refilled by removal of the marker from the animal and inserting ink through the inspection valve at top of tank.