The ability to properly chew and grind food is essential for nutrient digestion and absorption. Dysmastication is a condition involving impaired chewing- also known as mastication. [1]

Horses that are unable to chew properly may experience a cascade of problems affecting their nutritional intake, digestive system, and overall well-being. Horses with abnormal tooth wear or damaged or diseased teeth can also experience pain and discomfort. [2]

Diagnosing dysmastication involves observing the horse’s eating habits and conducting a physical examination. Additional diagnostic tools such as oral endoscopy, X-rays, and CT scans can provide further insights into a horse’s dental health.

Treatments for chewing disorders in horses may include:[5][2]

  • Dental floating
  • Tooth removal
  • Widening of tooth gaps
  • Surgical intervention
  • Pain management through medication

Dysmastication in Horses

Dysmastication in horses refers to any impairment or dysfunction in the chewing process. Horses with dysmastication may have difficulty chewing, or abnormalities in the way that they chew.

A horse’s teeth are essential for adequately grinding feed into smaller particles, a key step for efficient digestion. Any disruptions in a horse’s dentition can significantly impact their ability to eat and digest food properly.

Equine Teeth

Equine teeth are naturally adapted to their continuous grazing habits; growing continuously throughout their lives. Constant growth compensates for the wear and tear caused by chewing tough, fibrous plant materials, ensuring their teeth remain functional and effective for grinding feed.

However, this continuous growth can lead to imbalances if the teeth don’t wear down evenly. The diet and eating patterns of domestic horses might not provide the natural wear necessary, leading to uneven tooth wear.

Unfortunately, dental care for horses is often overlooked. Postmortem studies have frequently revealed undiagnosed dental issues in horses, highlighting a significant gap in equine healthcare. [15]

Signs and Symptoms

Signs of dysmastication or dental issues in horses can present in various ways including: [2]

  • Quidding: Dropping food from the mouth while chewing, often forming ‘balled up’ or ‘cigar-shaped’ masses.
  • Halitosis: Unpleasant breath odor.
  • Unusual facial expressions: Changes in facial expression may occur during chewing, potentially indicating pain or discomfort.
  • Weight loss: Loss of body condition ranging from mild to severe. Inadequate mastication can lead to reduced food intake and subsequent weight loss.
  • Changes in manure: Presence of long fibers in the feces, indicating inadequate digestion.
  • Behavioral changes: Irritability, reluctance to eat, or avoidance of specific types of feed. Affected horses may be resistant to having the bit placed in their mouth or respond to the bit negatively when ridden. Horses with dysmastication may also dip their hay in their water trough before eating it.
  • Excessive Salivation: Drooling or excessive production of saliva, potentially indicating oral discomfort.

Causes of Dysmastication in Horses

Dysmastication in horses can result from a range of factors, including poor tooth balance, dental disease, improper dental care, and systemic health problems.

Dental Issues

Dentition refers to the development, arrangement, and condition of teeth in a horse. It encompasses aspects such as the number, types, and structure of teeth, as well as their overall health and alignment within the mouth.

Horses are susceptible to a variety of dentition problems that can lead to difficulties in chewing. The risk of developing dental issues in horses tends to escalate with age.


Dental occlusion refers to the way the teeth in the upper (maxilla) and lower (mandible) jaws contact one another. [1] In horses, the standard occlusion (orthooclusion) is described as a level incisor bite. [6]

A malocclusion refers to any deviation from a typical occlusion pattern. Malocclusions in horses are categorized into classes from 0 to 4, with Class 0 indicating normal occlusion​. [7]

Malocclusion can result from uneven wear, congenital defects, or improper dental care. Additionally, the formation of dental abnormalities such as hooks, ramps, enamel points, and wave complexes can contribute to malocclusion.​ [9][5]

Horses grind their feed in a lateral and rostral (back to front) motion. This can result in uneven wear on their teeth and the formation of malocclusions. [8]

These malocclusions can disrupt normal tooth movement and impair chewing efficiency. They commonly result in elongated cheek and incisor teeth due to abnormal wear patterns. This can also increase the risk of periodontal disease.​[6][9]

Misaligned Teeth

Misaligned teeth are a common cause of malocclusion, manifesting as: [9][5]

  • Overbites
  • Underbites
  • Rotations
  • Crowding
  • Displacements
  • Tilting in both the incisors and cheek teeth

Parrot Mouth

Parrot mouth is a type of malocclusion that can result in dysmastication. It occurs when the lower jaw (mandible) is shorter than the upper jaw (maxilla). [3][4]

Cheek Teeth Diastemata

Spaces between teeth should naturally be tightly pressed together. When the spaces between teeth are wider than normal, they can trap food and promote gum inflammation.

Diastemata are a primary cause of dysmastication in horses. [3] They can form due to developmental factors (such as misalignment or overcrowding) or acquired reasons