Mostly likely not. Even though it is portable, I assume it is fastened to the foundation. However, if you were a tenant on the property and the barn was part of a "horse" related business that you are in, you may be able to argue it is a trade fixture. Work with your agent to see what is possible or consult with a real estate attorney. There may be ways to exclude it from a sale, IF you have not already received an offer, and IF the property is not in foreclosure.