Do not feed grass clippings to your horse. If you collect and compost lawn clippings, be sure the pile is out of reach of your horses. Here’s why:
Wet, green lawn clippings that have been left in a mower bag or in an exposed pile will start to mildew and ferment quickly. This can cause serious gastric problems in your horse’s gut, leading to a bout of colic.
Laminitis might be a risk too, particularly for horses with other risk factors like insulin resistance.
There’s also the possibility that the clippings contain lawn chemicals that are not suitable for ingestion. Toxic ornamental plants like yew or oleander can also be mixed in lawn clippings.
In addition, lawn clippings have a tendency to clump together in damp wads. A hungry horse may take a big mouthful and end up with a wad of hay stuck in its esophagus.
It’s ok, however, to leave clippings on your pasture after a mow. The clippings will dry out quickly when exposed to sun and air and they won’t accumulate in big piles. Horses can safely consume dry, well-distributed clippings along with pasture grass.