Equine Tax Parity Act of 2017 This bill amends the Internal Revenue Code, with respect to the preferential tax treatment of gains and losses from the sale of depreciable property used in a trade or business, to eliminate "horses" from the definition of "livestock" (thus making the 24-month holding period requirement for livestock inapplicable to horses and allowing horses to be treated as capital assets subject to the existing 1-year holding period requirement).