Effects of age and conditions of exposure on maternally mediated food selection by lambs

Abstract

We studied how age and conditions of exposure with mothers affected lambs' abilities to select and avoid foods. Ewes in the treatment group were allowed to eat Amelanchier alnifolia, but were conditioned, with lithium chloride, to avoid Cercocarpus montanus. Ewes in the control group were allowed to eat both foods. After the mothers were conditioned, lambs with their mothers were exposed for 5 min day −1 on 5 consecutive days to A. alnifolia and C. montanus offered simultaneously: the two shrub species were located at opposite ends of a 5 m × 5 m exposure pen. Half of the lambs in the treatment and control groups were 6 weeks of age and half were 12 weeks of age. During exposure. ewes in the treatment group did not ingest C. montanus, but ewes in the control group took nearly the same number of bites per 5 min of A. alnifolia and C. montanus. During exposure, lambs 6 and 12 weeks of age in the treatment group took fewer ( P<0.05) bites per 5 min of C. montanus than lambs in the control group. Following exposure, lambs were weaned and then tested 7 days later for preferences. Preference index (PI) values were calculated as the fraction of the total bites taken per 5 min of C. montanus. Treatment lambs exposed at 6 weeks of age had a lower PI for C. montanus than did control lambs during trials of 5 min day −1 for 7 days (PI=0.15 vs. 0.51; P<0.05), as did treatment lambs exposed at 12 weeks of age (PI = 0.19 vs. 0.53; P < 0.05). The PI for C. montanus did not differ for treatment lambs exposed at 6 or 12 weeks of age (PI = 0.15 vs. 0.19; P > 0.05). Nine weeks after exposure, the PI of treatment lambs for C. montanus was less ( P < 0.05) than that of control lambs. The average PI values for treatment and control lambs exposed at 6 weeks of age were 0.21 and 0.51, respectively, and the average PI values for treatment and control lambs exposed at 12 weeks of age were 0.28 and 0.47, respectively. Age of exposure did not affect the PI of lambs in the treatment groups for C. montanus (PI=0.21 vs. 0.28; P > 0.05). The results show that lambs offered two foods simultaneously took more bites of the food consumed by their mothers and less bites of the food avoided by the mothers.