Depreciate the % used for business use of transporting horses.  The personal pleasure use is not deductible.  As to the interest.  The business use portion would be reported on Schedule C or F.  The personal use portion of interest may be includible on Sch A as 2nd home.  Usually the purchase of these is for "Hobby Business", so convince taxpayers that the best way to survive an audit is to be reasonable and only take a % to business.