Relatively little is known about the ability of ungulates to visually discriminate vegetation patches while foraging on grasslands despite extensive studies with man-made stimuli presented indoors. This study aimed to assess visual discrimination ability of cattle (Bos taurus) under conditions closer to the actual foraging situation. Twelve Japanese Black cows were afforded four successive opportunities to choose between green and dead forages presented as 25 × 25 cm patches 1, 2, or 3 m ahead while walking through a 25-m-long field area. Apparatuses for presenting the forages as visual stimuli were designed to minimize olfactory cues. The green forage differed from the dead forage in appearance (color and texture) and quality (digestible dry matter and crude protein). Cows preferred the green forage to the dead forage and were able to use the forages as visual cues to discriminate them. The proportion of green forage choices was 0.70-0.72 (different from the chance at P < 0.001), 0.57 (P < 0.05), and 0.53 (P ≥ 0.1) at the distances of 1, 2, and 3 m, respectively. The results indicate that the ability of ungulates to visually discriminate vegetation patches during foraging in grasslands would not be as high as that expected from the visual acuity reported in the previous indoor studies.
Keywords: Cattle; Dead forage; Field locomotion; Green forage; Short distance; Visual discrimination.