The role of olfactory cues in the discrimination of agemates by lambs

We assessed the effect of olfactory cues on agemate discrimination between lambs, Ovis aries. In experiment 1, a local anaesthetic was sprayed into the nostrils of 2-3-week-old lambs to inhibit olfaction. To verify whether the treated animals were anosmic, they were tested for their responses to a food source tainted with the odour of dog faeces, a scent that is strongly avoided by intact lambs. In a simultaneous-choice test, lambs that were categorized as anosmic, i.e. that fed in the presence of dog faeces odour, responded preferentially to a familiar penmate over an alien agemate, indicating that olfaction is not essential for social discrimination. We then examined intact lambsʹ responses to pairs of agemates that were anaesthetized and partially hidden, thereby eliminating vocal and salient visual characteristics of the stimulus lambs, but allowing access to their odours. During the choice tests, subject lambs responded more positively to their familiar twin than to an unfamiliar, unrelated lamb, but they did not discriminate between a familiar, unrelated penmate and a strange stimulus lamb. Thus, olfactory cues appeared to be a sufficient basis for twin recognition in this context. We conclude that discrimination of a twin but failure to discriminate between familiar and unfamiliar unrelated lambs probably reflects differential familiarity between twins and unrelated penmates, but perceptible similarities between the odour phenotypes of twins may also facilitate the discrimination.