Discrimination learning in sheep with cues varying in brightness and hue

Discrimination learning ability of sheep ( Ovis aries L.) was studied with cues that varied either in brightness or hue. The hues tested were green and yellow, characterlstic of vegetation which sheep eat. The three sheep tested successfully learned to discriminate between pairs of cue cards of different brigthnesses: 41% or 77% reflectance. None of the sheep learned to discriminate between pairs of cue cards which were either green or yellow of the same brightness. The results do not discount the possibility that sheep possess colour vision. The ability to discriminate brightness may be one part of the mechanism allowing sheep to select more nutritious vegetation on an intraspecific basis. Brightness is correlated significantly with protein content in perennial ryegrass ( Lolium perenne L.).