Case description: A 15-year-old Saddlebred gelding used for competitive pleasure driving had a 1-year history of head shaking while pulling a cart.
Clinical findings: The horse had cystic corpora nigra in both eyes and concomitant classic and operant conditioned responses to wearing a bridle with bilateral eye covers (blinkers).
Treatment and outcome: Deflation and coagulation of the cysts with an infrared diode laser and behavior modification consisting of desensitization and counter-conditioning were used to successfully restore performance.
Clinical relevance: Behavioral changes in horses can result from a combination of physical and psychologic causes. A combination of appropriate medical treatment of physical abnormalities and a behavioral modification plan is necessary to successfully treat behavioral problems in these patients.