Effect of an energy supplementation and time on use of medusahead by grazing ewes and their lambs.

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Rangeland Ecology and Management







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Medusahead is an annual weed that invades millions of acres in the western United States. This study explored the effect of energy supplementation on use of this unpalatable weed by ewes and their lambs. Thirty-six ewes with their lambs (2 − 3 mo old) were randomly assigned to 12 groups (3 ewes with their lambs per group), and half of the groups received 2.5 kg group d− 1 of an energy-based supplement (beet pulp − barley − Ca-propionate, 66:30:4; as-fed basis). After supplementation, all groups grazed plots with medusahead infestation for 15 d. Lambs were then weaned, kept in the same groups but without supplementation, and allowed to graze medusahead-infested plots for 3 d. Grazing events were recorded daily at 5-min intervals, and defoliation of medusahead tillers was measured in all plots. The proportion of grazing events recorded on medusahead and the proportion of defoliated medusahead tillers were not affected by supplementation in either ewes or lambs (P > 0.05). All ewe-lamb groups presented a greater proportion of medusahead use during the second half of the grazing period (P < 0.05). Nevertheless, the average proportion of events recorded for medusahead use was never greater than 7%, which was similar to the relative availability of medusahead in the community (i.e., 6%). Use of medusahead by ewes was correlated with that observed for their lambs (r = 0.83; P < 0.05), and weaned lambs showed a similar proportion of grazing events on medusahead to those observed before weaning (P > 0.05). These results suggest that mothers influence medusahead use by their offspring. They also suggest that despite the low palatability of medusahead, sheep will not avoid medusahead when grazing moderately infested rangeland. The diversity of the plant community likely contributed to this outcome, which might have also reduced the impact of the supplement on medusahead use by sheep.