This is a condition that is seen quite commonly and ranges from mild to severe.
Parrot Mouth or Brachygnathia, is when the lower jaw is shorter than the upper jaw leading to an overbite. This typically causes malocclusion of the incisors and often only a mild malocclusion of the cheek teeth. Horses with Parrot Mouth tend to be more prone to incisor related periodontal disease as well as exaggerated hooks on their cheek teeth. Regular dentistry helps to maintain a healthy mouth and happy horse.
Baker, G.J & Easley, J. (1999) Equine Dentistry. London, UK: WB Saunders
Navara, Katie. “Common Equine Dental Problems and How To Avoid Them: Equimed – Horse Health Matters.” EquiMed, Katie Navara, 19 Apr. 2017, equimed.com/health-centers/dental-care/articles/common-equine-dental-problems-and-how-to-avoid-them.