The mouth
One area that’s often overlooked when we discuss nutrition is the mouth, but this truly is the start of the digestive process and issues here will affect the rest of the system.
Lips
The horse’s lips are put to a very good use and horses are particularly good at being able to select small bits out of their feed that they don’t like.
They use their prehensile upper lip to grasp the grass tips. They then curl their lips inward and deliver the grass to their teeth.
The teeth
Overall anatomy
Horses are heterodontous, which means that they have different shaped teeth for different purposes.
Incisors are found at the front of the mouth, and these are used primarily for cutting and ripping food, most commonly grass.
Immediately behind the front incisors is the interdental space, where no teeth grow from the gums. This is where the bit sits.
Behind the interdental space, all horses also have twelve premolars and twelve molars, also known as cheek teeth. These teeth grind food bitten off by incisors, prior to swallowing.
A typical adult horse thus has 40-42 permanent teeth, dependent on the presence of wolf teeth (otherwise known as canine teeth).
Mares may only have 36 to 40 teeth as mares are less likely to have canine teeth.
Only 10-32% of horses are actually thought to develop wolf teeth.
Wolf teeth are more common on the upper jaw, and can present a problem for horses in work, as they can interfere with the bit. They are frequently removed for this reason.
Chewing surfaces
One thing to note is that the horses’ chewing surfaces are not level.
The upper and lower cheek teeth meet at around a 10- to 15-degree slope, which facilitates the strong grinding forces necessary to breakdown fibrous feed.
The incisor teeth, which are not used for grinding, should meet in a more flat fashion.
Jaw movements vary depending on the height at which horses eat.
Eating from floor level promotes a natural rotation of the jaw and can help promote a more natural tooth wear.
Abnormal wear patterns limit chewing efficiency and this is why routine dental checks are important.
The structure of the tooth itself
Horses have what we call hypsodont teeth.
This refers to the fact that a portion of the tooth (around 10cm) sits below the surface of the gums hidden in the bone of the jaws.
The grinding action of the molars and premolars in particular, wears away a little bit of tooth surface, and more emerges into the mouth to take its place.
This means that as the horses ages the tooth will become progressively shorter until there becomes a time when very little of the tooth remains, and the older horse might have difficulty eating.
As a rough estimate, a horse’s teeth will wear and a new tooth surface will replace it at a rate of around 3-4 mm each year. This means that the horse should have enough tooth to last around 25 years under “ideal” circumstances.
For horses, “ideal” circumstances include, exposure to a diet of mainly soft grasses, but including harder/coarser varieties; some grains; broad leaf plants and the fine sand-like silicates that accompany these plants; and most importantly, exposure to these forages 24 hours a day, 365 days a year.
This environment helps to ensure that a horse will wear his teeth evenly and maintain good dental health.
The role of dentistry
Not all modern equines live under such ideal circumstances, and so modern equine dentistry is evolving to make up for the imbalances.
The exposed crown of an adult horse’s permanent tooth has neither a central nervous structure nor a blood supply.
Thus, when it is treated, the horse feels no pain, allowing dentists to work pretty effectively on the horse’s mouth even without sedation.
If the teeth are in good order this ensures the horse will be able to extract maximum benefit from his food.
Food that is not correctly chewed can predispose a horses to conditions such as choke and even colic.
Signs of a tooth issues can include:
- Quidding (dropping of food from the mouth)
- Reduce appetite
- Weight loss
- Reluctance to eat certain feedstuffs
- Unusual jaw movements
When a foal is born, it normally has no teeth, but this only lasts for a short while and within the first week of life teeth start to appear through the gum.
By the time the horse reaches 4-4.5 years these “baby” teeth will have been replaced with permanent teeth.
Because the baby teeth, are shed in the order in which they arrive, they provide a good marker for determining a young horse’s exact age.
Did you know?
The rate at which a horse chews is referred to as a ‘jaw sweep’. Horses typically take 60,000 jaw sweeps per day if grazing constantly. The type of grass, time spent feeding and the size of the horse will all influence the rate at which a horse consumes his grass. The average 500kg horse takes 40 minutes and 3,400 jaw sweeps to consume 1kg of hay.
Dental care tips
Dental care tips:
- Dental care should start at birth with at least a visual inspection of the foal’s mouth during the veterinarian’s first examination.
- A complete dental exam should be done by the time the horse is 12-18 months old.
- Adult horses should get maintenance care at a minimum of 12 monthly intervals.
Older horses should have checks performed at least every six months especially if they are prone to issues.
The saliva
Breaking food down into small particles (around <2mm) by chewing begins the process of digestion.
Saliva is then produced and the process of chewing allows these smaller particles to become lubricated with saliva ensuring the bolus of food can be easily passed down the oesophagus into the stomach.
Three pairs of salivary glands produce the saliva and on average up to 35-40 litres of saliva could be produced per day.
Saliva is made up of water, bicarbonate and amylase – which assist respectively in lubricating swallowed food, the buffering of the acid in the stomach and, to some extent, the digestion of carbohydrates. However, the main purpose of the saliva is to help move the food through the oesophagus easily and to buffer the stomach acid, as the actual levels of the enzyme amylase in the saliva are low in horses compared to in other species.
An interesting fact to note is that unlike humans, horses can secrete saliva only when they chew.
This is important as saliva helps to buffer stomach acid which is continuously produced in the horse, whether or not food is present.
This is why it is recommended that horses have access to forage 24/7 to ensure not only that their natural instincts are satisfied, but also that they can continuously have something to chew on so they produce adequate saliva to help buffer the stomach acid produced, reducing the risk of ulceration.
Saliva is produced at different rates depending on the feed stuff present. For example, it takes more chews to breakdown long stemmed hay and thus more saliva is secreted.
Concentrate feeds take less chews to consume and thus less saliva is secreted, and so once again its easy to see the importance of forage.
Did you know?
Ever wondered why domesticated horses are so prone to developing sharp edges on their teeth?
When chewing on hay or any other paddock vegetation, the horse chews with long jaw sweeps.
When feeding on grains and concentrates, much shorter jaw sweeps are required and so the outer edges of the teeth are not naturally filed down, therefore resulting in the development of sharp edges.
This is why horses who live out and constantly graze rarely develop sharp edges on their teeth, and domesticated horses have to have regular floating from a dentist in order to maintain their teeth.
After the mouth
After the food has passed through the mouth it moves down the oesophagus into the stomach, which is where our journey takes us next.