To determine the impact of occasional or repeated packhorse (Equus caballus) grazing on mountain meadows in southwestern Montana, Olson-Rutz et al. evaluated vegetation use and diet selection for horses that were tied to a picket and allowed to graze on a 15 m rope for 4-, 8-, or 18-hours during July, August, or September. Picketed horses fed avidly for 3 to 4 hours and continued to graze intermittently thereafter throughout their time on picket circles. They moved continuously while grazing, even when preferred forages were available. As grazing time increased the percent of grasses grazed increased and the height of grasses was reduced (less than 12 cm tall), especially in circles grazed more than 8 hours or grazed repeatedly during the summer. Packhorse grazing does have immediate impacts on the vegetation in mountain meadows, however, the authors suggest that the impact level will vary with the horse's previous exercise and picket grazing experience, and the amount of time they are picketed in one circular area.
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