Original sentence: The kiang’s hooves look like those of a horse but wider. They are wide and don’t slip on rocks.
Corrected sentence: The kiang’s hooves look like a horse’s but are wider. They help the kiang not slip on rocks.
Why this is better: We use "a horse’s" to show the hooves belong to a horse, and saying "help the kiang not slip" makes it clear the wide hooves keep the kiang from slipping on rocks.