Development of an apparatus for evaluating the visual and olfactory discrimination ability of cattle under controlled...

Ungulates visually and olfactorily discriminating between vegetation patches in grasslands often encounter restriction of target visibility due to light intensity changes; however, little is known about their performance in such a context. We developed and tested an apparatus for evaluating the visual and olfactory discrimination ability of cattle under controlled target visibility, focusing on the discrimination at a short distance. The apparatus was designed to contain a discrimination target under a sliding cover of variable light transmission levels and behind a vent of a fixed size and aperture so as to control the visibility of the target (14-100% restrictions) while ensuring a constant level of odor. Twelve Japanese Black cows were allowed to choose between two apparatuses presenting a pair of targets: green forage versus empty, green forage versus dead forage, or green forage versus green-dead mixture. Cows rapidly learned to slide open the cover to reach the selected target, consistently chose the green forage against the alternative except against the green-dead mixture under 100% visual restriction, and remembered the reaching procedure for at least 16 days. The results indicate the usefulness of the apparatus for assessing close visual and olfactory discrimination ability of cattle in detail.