COMPARISON OF SHEEP AND GOAT PREFERENCES FOR LEAFY SPURGE

The objective of these studies was to compare preference for leafy spu rge (Euphorbia esula L.) by sheep and goats. Study 1 was a choice test that paired leafy spurge with either arrowleaf balsamroot (Balsamorhi za sagittata (Pursh)Nutt.) or crested wheatgrass (Agropyron cristatum (L.)Gaertn.) for a 30 minute feeding period. Study 2 consisted of 3 gr azing trials on spurge-infested pastures. Differences between sheep an d goat grazing were measured using capacitance meter estimates of stan ding crop and ocular estimates of composition; counts of grazed and un grazed leafy spurge stems; and bite counts to estimate botanical compo sition of diets. The paired choice study showed that selection for lea fy spurge was affected by the interaction (P<0.0001) of animal species and the choice alternative. Goats preferred leafy spurge (80% of cons umption) compared to arrowleaf balsamroot, but demonstrated a relative avoidance (33% of consumption) of leafy spurge when paired with crest ed wheatgrass. Sheep always avoided leafy spurge compared to the alter native forage and consumed an average of only 28% of their intake from leafy spurge during the 30 minute test. In the grazing trials goats t ook 64% of their bites from leafy spurge compared to 20% for sheep. Th is represented a relative preference for spurge by goats compared to a strong relative avoidance by sheep. Sheep avoided areas in the pastur e that had high densities of flowering spurge stems while goats were r elatively unresponsive to stem densities. Goat grazing reduced the num ber of flowering stems. Stem numbers were 90 vs. 23 flowering stems m- 2 (P=0.4) in sheep- and goat-grazed pastures, respectively. Goats appe ar to have a greater potential for biological control of leafy spurge than sheep. This advantage may be particularly important in areas wher e leafy spurge is relatively unpalatable, which the present study site represented.