We studied the effects of mother's preference and lamb age on selection of Amelanchier alnifolia and Cercocarpus montanus by lambs. Thirty-six ewes and their lambs were divided into treatment and control groups. Mothers in the treatment group were conditioned to eat A. alnifolia, but avoid C. montanus, by pairing ingestion of C. montanus with lithium chloride (LiCl), a compound that causes gastrointestinal distress. Mothers in the control group were allowed to eat both foods with impunity. After ewes were conditioned, lambs were exposed daily for 5 days with their mothers to either A. alnifolia or C. montanus for 5 min followed by a 5 min exposure to the other food. Half of the lambs in the treatment and control groups were 6 weeks of age during exposure, while the other half were 12 weeks of age. Treatment lambs of both ages ate less C. montanus than control lambs during exposure. Lambs were weaned after exposure and tested 10 days later for preference. Preference indices (PI) for C. montanus were calculated as the percentage of total bites contributed by C. montanus. Treatment lambs exposed at 6 weeks of age ate less C. montanus than A. alnifolia compared with control lambs during trials of 5 min day-1 for 7 days (PI = 0.07 vs. 0.44; P < 0.05). Treatment lambs exposed at 12 weeks of age also ate less C. montanus than A. alnifolia compared with control lambs (PI = 0.26 vs. 0.45; P < 0.05). Lambs that were 12 weeks of age during exposure, however, ate more C. montanus than lambs exposed at 6 weeks of age (PI = 0.26 vs. 0.07; P < 0.05). Nine weeks after exposure, treatment lambs exposed at 6 weeks of age still showed lower preference for C. montanus than for A. alnifolia compared with control lambs (PI = 0.10 vs. 0.48; P < 0.05). Treatment and control lambs that were 12 weeks of age during exposure, however, showed equal preference for C. montanus and A. alnifolia (PI = 0.42 vs. 0.42; P > 0.05). We conclude that lambs 6 weeks of age were influenced more by their mothers dietary habits than were lambs 12 weeks of age.
