You come home after being gone for a few hours and your horses, who have been turned out on pasture all day, are found eating a large pile of lawn clippings near the fence line adjacent to the road. It appears that a passerby thought they were treating the horses by disposing of their excess grass in the pasture unaware of the serious potential risks this poses. What is the primary medical concern, and what treatments options may the vet recommend when they arrive at the farm?