If your horse has white plaque on the inside surface of his ears, don’t get too worried about it. Varying from white or non-pigmented, slightly raised to distinct “bunch of grape-like” lesions, this ear plaque is a type of wart (papillomatosis virus) that rarely causes problems, and treatment is usually unnecessary. While ear plaque typically doesn’t get worse, it usually doesn’t go away either. Contact your vet for a definitive diagnosis.
Horse Ear Plaque
What to do about that strange white substance in your horse's ear.
My horse has this and my vet told me to use black shoe polish to cover it for shows because she is bay and the wart is white. Has anyone tried this yet and if so what were you results?