You Feed To, Or Allow A Horse To Eat Grass Clippings

Fresh lawnmower clippings are actively fermenting, which is why they feel warm. The horse doesn’t need to do much chewing since the grass is already small, and without saliva to reduce the clippings, the fermentation proceeds unabated in the horse’s stomach, much ahead in the digestive tract than normal. The gas given off by the fermentation can cause colic, in some cases so severe that the stomach may rupture.  Source: