Visual identification of small sizes by adult dairy bulls

The objective of these trials was to measure the visual acuity of adult dairy bulls using a psychophysical approach. Three adult dairy bulls (2 Holstein Friesian and 1 Red Holstein) were trained to recognize a black disk and then to differentiate between that disk and a black annulus that had a white center. The diameter of the center of the annulus varied from 30 to 0.5 cm. Bulls could identify a white center as small as 1 cm. Because bulls had to discriminate between the black disk and the black annulus at a distance of at least 1.5 m, we calculated a visual angle of 23' (arc minutes) to describe the visual acuity of the bull. This acuity is much poorer than that of other ungulates, such as sheep, and even poorer than the acuity of younger cattle.