Instructions
Look for golf-ball-sized pellets. They might be stuck together or they might be broken apart from hitting the ground. There will be multiple pellets to form a cluster of horse poop. The size of this cluster of pellets will vary by horse.
Note the color. Horse poop will be brown and may be tinged with green depending on the horse's diet. All horse poop will have some hay or grass inside it.
Notice the lack of smell. Because horses are herbivores, their poop won't smell like a carnivore's does. There are also no health risks associated with horse poop, so cities with mounted police don't have to worry about immediate clean up.
Look at the soil. Horse poop is mostly water and is completely biodegradable. This means that horse poop will degrades into the soil around it, fertilizing the grass.
How to ID Horse Poop
Horses are big animals and they release a lot of poop. But you don't have to live in the country to identify it. It looks completely different than cow poop and it's big. Both make it easily identifiable in a pasture. The average horse of 1000 pounds produces 50 pounds of poop a day. This accumulates to 8 to 10 tons every year.