Training lambs to be weed eaters: Studies with leafy spurge

The objective of the study was to determine if exposure of young lambs to leafy spurge (Euphorbia e&u L.) would increase the consumption of this plant. Orphan lambs were exposed to leafy spurge from birth to 11 weeks of age as a water soluble extract mixed with milk replacer and as freshly harvested plants. Ewereared lambs were exposed to leafy spurge by grazing them on a leafy spurge-infested pasture. Study 1 investigated the consumption of vegetative and flowering leafy spurge paired with arrowleaf balsam root (Balsamorhiza sagiftata (Pursh)Nutt.) by orphan lambs during a 30-mm feeding period. Experienced lambs consumed a higher percentage leafy spurge than naive lambs (P<O.O3). The interaction of leafy spurge phenophase and previous experience (X0.02) showed that experienced lambs preferred leafy spurge regardless of phenophase (70% of intake) and naive lambs only preferred leafy spurge when it was vegetative. Study 2 investigated the preference for leafy spurge on pastures with high or low leafy spurge biomass. Experienced compared to naive lambs had a higher percentage of bites (P<O.OOl) and preferred leafy spurge in the high spurge biomass pasture, but not in low biomass pastures. Naive lambs avoided leafy spurge in both pastures. Study 3 was a pasture trial that investigated spurge consumption by orphan and ewe-reared lambs. Percent bites and time spent grazing leafy spurge were not affected (C-0.23) by previous exposure, but daily herbage removal was greater (P<O.O9) in pastures grazed by experienced compared to naive lambs (876 vs. 685 g/lamb, respectively). Experienced ewe-reared lambs had a higher rate of biting on leafy spurge (PCO.06) than naive or orphan Lambs. These studies indicate that previous experience will be an important factor affecting the use of sheep as a biological control agent for leafy spurge.