Socially induced food avoidance in lambs: direct or indirect maternal influence?

Food avoidance can be directly motivated in the sense that an animal refrains from eating a food because of an aversion to it, or indirectly motivated in the sense that an animal ingests little of one item because it prefers another. We studied whether the reluctance of a lamb to eat a shrub (Cercocarpus montanus) its mother avoided resulted from a socially induced aversion to C. montanus or from a socially induced preference for an alternative shrub (Amelanchier alnifolia). Each lamb (n = 6) in the treatment group was exposed with its mother to either A. alnifolia or C. montanus for 5 min, followed by 5 min of exposure to the other food for 5 d. Mothers in the treatment group avoided C. montanus because its ingestion had previously been paired with lithium chloride, but they readily ate A. alnifolia. Each lamb in the control group (n = 6) was exposed with its mother to only A. alnifolia. Following weaning, lambs in both groups strongly preferred A. alnifolia to C. montanus when offered a choice between the two species (P < .05), but they readily ate C. montanus when only C. montanus was offered. Accordingly, the data support the hypothesis that the low consumption of C. montanus occurred as a result of a socially induced preference for A. alnifolia, not as a result of a socially induced aversion to C. montanus. If food avoidance had been directly mediated, lambs whose mother avoided C. montanus would have completely avoided the shrub during testing, as in the case when acquired food aversions are directly mediated by toxins.