Teeth: how horses' teeth work

Teeth that keep coming

The Royal Veterinary College describes horses' teeth as specially adapted for a life of grazing and designed to grow continuously throughout life. Grass and hay are tough, and World Horse Welfare explains that the teeth must grind them down to around 3 mm before the food reaches the stomach, so they wear constantly. Horses have adapted to that wear with a large reserve of tooth below the gum line, which keeps emerging (erupting) over the horse's life to replace the surface that is worn away.

The British Horse Society puts some numbers on it:

• Horses can chew around 30,000 times a day.
• That chewing wears the teeth down by about 2–3 mm a year.
• Horses are born with deep tooth roots, which get shorter as the teeth erupt.

Because a horse has only so much reserve crown, the teeth of an old horse are shorter and can become loose or displaced. Older horses also tend to have smoother chewing surfaces, so they may struggle to grind food as well, and they more often have decay and gaps between their teeth.

How many teeth?

Adult horses have between 36 and 44 teeth, and males have more than females. They fall into two working groups:

• Incisors, at the front, cut the grass. The lips and tongue gather forage and pass it to them, and World Horse Welfare notes that problems here can stop a horse feeding properly at pasture or from a small-holed haynet.
• Cheek teeth (premolars and molars), at the back, grind food. The tongue moves food back to them for chewing.

Many horses also have small wolf teeth. The British Horse Society notes they can interfere with the bit and cause discomfort, which is why checks before a young horse is first bitted are especially important. The Royal Veterinary College lists wolf tooth extraction among the minor surgery it carries out on yards.

How vets number teeth

Vets record each tooth with a number in the Triadan system. The last two digits show where the tooth sits in its row, counting back from the centre of the mouth:

A dental chart using these numbers lets a vet or technician record exactly what was found and treated, and compare it at the next visit.

Chewing power

World Horse Welfare says the force of a horse's chewing often exceeds 150 kg. If there are gaps between the teeth, food can be forced deep into them. That is how periodontal (gum) disease starts, which World Horse Welfare calls probably the most common and most painful equine dental disease. It is the main reason horses drop feed (quidding) and lose weight with dental disease.

Hidden pain

Horses are prey animals and are skilled at hiding pain, especially dental pain. The British Horse Society cites research suggesting that 70% of horses may have undiagnosed dental pain. Signs, when there are any, can include:

• dropping food, pouching food in the cheeks, chewing on one side or drooling
• changes in behaviour at rest or at work, including headshaking or resisting the bit
• swelling of the face, discharge or a smell from the nostrils, or red, swollen gums
• choke, weight loss or poorer performance

The Royal Veterinary College adds that a horse that suddenly can't bite through a carrot may need its teeth checked. Many horses with serious dental problems show no outward signs at all.

Who should check them, and how often

In the UK, anyone can legally rasp a horse's teeth, but it is a specialised skill. The British Horse Society and World Horse Welfare advise using a vet (ideally an equine vet) or an equine dental technician who belongs to the British Association of Equine Dental Technicians or is a category 2 member of the Worldwide Association of Equine Dentistry.

Advice on how often differs a little:

• World Horse Welfare: every six months for horses under eight and over eighteen, and every twelve months between those ages if there are no concerns.
• British Horse Society: every nine to twelve months, with older horses and those with dental problems checked as advised by the vet or technician.
• Royal Veterinary College: at least once a year, starting from around two years old so that the eruption of the adult teeth can be monitored.

The British Horse Society also advises checking foals for developmental problems, with more thorough checks and rasping often starting from 18 months, and checking a newly bought horse's teeth as soon as possible.

Modern equine dentistry goes well beyond rasping. The University of Edinburgh's equine dental clinic, for example, carries out root canal treatment of fractured teeth, fillings, extractions of cheek teeth and orthodontic braces for foals with a "parrot mouth" (an overbite).

For how chewing fits into digestion, see The digestive system.