Comparison of sheep and goat preferences for leafy spurge

Abstract

The objective of these studies was to compare preference for leafy spurge (Euphorbia esula L.) by sheep and goats. Study 1 was a choice test that paired leafy spurge with either arrowleaf balsamroot (Balsamorhiza sagittata (Pursh) Nutt.) or crested wheatgrass (Agropyron cristatum (L.)Gaertn.) for a 30 minute feeding period. Study 2 consisted of 3 grazing trials on spurge-infested pastures. Differences between sheep and goat grazing were measured using capacitance meter estimates of standing crop and ocular estimates of composition; counts of grazed and ungrazed leafy spurge stems; and bite counts to estimate botanical composition of diets. The paired choice study showed that selection for leafy spurge was affected by the interaction (P < 0.0001) of animal species and the choice alternative. Goats preferred leafy spurge (80% of consumption) compared to arrowleaf balsamroot, but demonstrated a relative avoidance (33% of consumption) of leafy spurge when paired with crested wheatgrass. Sheep always avoided leafy spurge compared to the alternative forage and consumed an average of only 28% of their intake from leafy spurge during the 30 minute test. In the grazing trials goats took 64% of their bites from leafy spurge compared to 20% for sheep. This represented a relative preference for spurge by goats compared to a strong relative avoidance by sheep. Sheep avoided areas in the pasture that had high densities of flowering spurge stems while goats were relatively unresponsive to stem densities. Goat grazing reduced the number of flowering stems. Stem numbers were 90 vs. 23 flowering stems m2 (P = .04) in sheep- and goat-grazed pastures, respectively. Goats appear to have a greater potential for biological control of leafy spurge than sheep. This advantage may be particularly important in areas where leafy spurge is relatively unpalatable, which the present study site represented.