Horseracing Integrity Act of 2019 This bill establishes the Horseracing Anti-Doping and Medication Control Authority as an independent, private non-profit corporation with responsibility for developing and administering an anti-doping and medication control program for (1) Thoroughbred, Quarter, and Standardbred horses that participate in horse races; and (2) the personnel engaged in the care, training, or racing of such horses. The Federal Trade Commission shall have oversight over the authority. An interstate compact may be established after five years to take over the authority's duties. The sale of a Thoroughbred, Quarter, or Standardbred horse shall be considered an unfair or deceptive act or practice if the seller (1) knows or has reason to know the horse has been administered a substance that the authority determines has a long-term degrading effect on the soundness of the horse, and (2) fails to disclose to the buyer the administration of such substance.