Horses are herbivores that eat roughage and grain primarily. If you want to add to their diet, especially by way of treats, be aware of the following points: Too much fruit is a bad thing. Some riders will use apples as treats for their horses. Although an occasional apple is likely fine, too much fruit can cause colic or lead to founder. Don't feed your horse meat. Horses are herbivores and have developed systems designed to digest only plants. Don't feed your horse lawn clippings. Although horses may graze in the same grass, giving grass material to them all at once can cause colic or make them choke. Don't feed your horse dusty or moldy hay. Giving your horse dirty hay can make it sick. Even if the amount of dust or mold is minimal, eating it could lead to the horse developing serious lung issues.