Whether your horse is of modest or of competitive class value, you will want a policy to cover the illness of your horse, your tack, and your liability to the public ( which is not normally covered by your house insurance). You may also want to arrange cover for accident to the rider, and for motor insurance on your horse box.
Having a horse rider in the family means expense in many directions. Insurance is one of the few animal related expenses there can be some control over.
Cover can include death, illness, disease and straying of the horse, and activities all the way from hacking to serious eventing.