Parrot mouth is a common equine dental condition typically identified at birth or shortly after. It is characterized by a pronounced overbite where the horse’s upper front teeth protrude beyond the lower row of teeth, causing the upper lip to overlap the lower one.

Dental misalignment in cases of parrot mouth is due to anatomical abnormalities in one or both jaws of the affected horse’s skull. The underlying causes of this condition are currently not fully understood.

While some degree of dental misalignment is normal and often harmless, severe cases of parrot mouth can impede a horse’s ability to bite and chew, leading to issues such as weight loss, injury to the roof of the mouth, and digestive problems.

Understanding the anatomy of a horse’s mouth and recognizing the signs and severity of parrot mouth can help horse owners ensure their horse receives timely diagnosis and treatment. Early intervention, including dental modification and surgical procedures, can significantly improve the quality of life for affected horses.

Parrot Mouth in Horses

Parrot mouth is a condition in horses where the upper front teeth protrude out further than lower front teeth. [1][2][3][4] The upper lip overlaps the lower one, which can make the profile of the horse resemble a parrot’s beak. [5][6][7]

This condition is also known as: [3][5][6][7][9][10][11]

  • Rostral malocclusion
  • Brachygnathism
  • Brachygnathia inferior
  • Prognathia superior
  • Retrognathism
  • Overshot jaw

As with all skeletal structures, there is variance in presentation of jaw alignment between individual horses. In horses with ideal alignment, the upper front teeth and the lower front teeth meet evenly when the jaws are closed and the head is in a neutral position. [6]

Parrot mouth is the result of abnormalities in jaw bone morphology. Specifically, parrot mouth is due to one or a combination of the following morphological presentations: [1][5][8][9]

  • Upper jaw bone is abnormally long
  • Lower jaw bone is abnormally short

Many horses have some degree of misalignment of their front teeth without significant impact on quality of life. Temporary changes in dental alignment related to head position are also normal. [6]

Parrot mouth requires veterinary attention if misalignment of the jaws leads to difficulty eating or tissue damage in or around the mouth due to overgrown teeth. [3]

Overbite vs. Overjet

Parrot mouth is typically used as a general term that encompasses two abnormalities in the position of the horse’s upper and lower jaws: overbite and overjet. [12]

  • Overbite: In horses with overbite (also known as an overshot jaw), there is vertical misalignment of the front teeth. The upper front teeth overlap and sit in front of the lower front teeth when the mouth is closed. [1]
  • Overjet: In horses with overjet, there is horizontal misalignment of the front teeth. The upper teeth protrude further forward than the lower front teeth when the mouth is closed, leaving a space between the upper and lower front teeth. [1] Some horses with an overjet develop an overbite as well due to wear on specific teeth and overgrowth of others. [3][5]

While parrot mouth is often used to describe both overbite and overjet, some sources reserve the term only for overjet and specify overbite as a different condition. [5]

Equine Mouth Anatomy

The horse’s mouth anatomy has evolved for efficient grazing and breaking down fibrous plant material.

To support this feeding behavior, the teeth perform two primary functions: biting, which involves cutting through material with the front teeth, and chewing, which involves grinding the material into smaller particles using the back teeth. [10]

Changes to the structures of the horse’s teeth and jaws resulting from parrot mouth can impact these functions. Horse owners benefit from understanding the specifics of equine tooth anatomy and function to better recognize when misalignment warrants further investigation.

Equine Dentition

Adult horses have hypsodont teeth. These teeth are common in mammals that wear down the enamel by eating abrasive material, such as coarse forage. [10]

In hypsodonts, the tooth enamel extends well past the gumline and continually erupts throughout life as the grinding surface wears away. Due to this continual tooth eruption, domestic horses require routine dental floating to keep their teeth balanced so they can adequately chew forage. [10]

Proper chewing is an essential first step in equine digestion, helping to ensure feed particles are small enough for the digestive tract to handle.

Incisors

Incisors are flat, spade-like teeth at the front of the mouth that are used for biting. [10] In cases of normal alignment, the upper and lower incisors meet evenly to allow effective biting.

In a horse with parrot mouth, the upper incisors are further forward than the lower incisors. This means the horse cannot bite as effectively. In severe cases, the ability to bite is significantly impaired. [9]

If the lower incisors get trapped on the inside edge of the upper teeth, growth of the teeth and movement of the jaw can become limited. [1][3] This can impact the horse’s ability to chew. [3]

In some cases, the line of the upper incisors becomes curved due to uneven wear. In these cases, the row of teeth are described as having a “smile” or a “frown”.