Probably not, unless you have specifically requested this be added to your policy and have paid
an additional premium.  If you are allowing a horse organization to use your property, you can request
evidence of their Liability Insurance and request to be added to their policy as an Additional Insured.
Daily Equine Event policies are available to cover these kinds of functions, or the horse organization
may have an annual Liability policy to cover all their various shows and events and can provide you
with evidence of their insurance.