It depends on what "work on the Ranch" means.
If a W-2 employee, job expenses are not deductible, and assets purchased for the job are not depreciable.
If you are self employed or a contract employee, the horse is depreciable property, as explained in the other answer.
If you are the ranch owner, the ranch must be an income generating activity, for you to claim deductible expenses or depreciate assets.
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