The horse evolved around 52-53 million years ago on the plains of north America. Back then, what we know as the horse was a very small animal, about the size of a rabbit. It had four toes and lived in the forest. It’s teeth were small and designed to deal with a diet that mainly consisted of soft fruits, foliage and leaves.
Due to climatic changes around 50 million years ago, the forage and plants in its environment changed greatly to one of tundra and course grasses. So, the diet went from consisting of soft and simple proteins and carbohydrates to a rough and high forage diet.
Carbohydrates are made up of molecules of sugar, simple carbs like glucose and starch and complex carbs such as cellulose. Cellulose is the important one here as it’s a structural carbohydrate that gives the grass its strength and allows it to grow tall.
No animal in the world can digest Cellulose, even though it’s the most common carbohydrate in foodstuffs! And the horse’s diet is very high in Cellulose.
The horse’s digestive system evolved to cope with Cellulose by developing a large bowel full of bacteria and microbes that assisted in the digestive process. This caecum and colon developed into a large fermentation vat that is able to break down the cellulose into volatile fatty acids that the horse can then utilise.
A horse’s gut is termed ‘Low efficiency’ because its designed to digest this low energy fibrous diet. Horses need to browse and trickly feed for 16+ hours a day on a high forage diet in order to keep the colon full and digesting effectivly.
It’s extremely important that this high cellulose forage, grass and hay, is physically broken down into very small particles because the bacteria in the hind gut need a large surface area to do their digestive work.
The optimal particle size for digestion in the hindgut is 2mm long, and the horse’s teeth have evolved to do this job very well!
This means that the teeth need to be functioning optimally in order to grind this rough forage down to the ideal size for complete digestion to occur.
Chewing is described as Mastication, the act and process of the jaw and teeth in chewing, crushing and mashing food into smaller digestible pieces.
When we look at the process of Mastication in the horse, we know that a Pony has 8000 mastication’s per kilogram of forage. This equates to 50-60,000 mastication’s per day to break up the forage into suitable particle sizes for the effective fermentation in the large intestine.
Horses teeth also get a lot of wear, there are two factors to this:
FIRST They are masticating for up to and over 16-20 hrs a day.
SECONDLY Forage contains tiny ‘grit’ like substance called Phytoliths which is abrasive silica particles taken up from the soil into the plants. This Silica and also dirt contamination can wear the teeth quickly. Horses will generally try very hard to avoid eating silica/dirt in order to prevent excessive wear.
Horses teeth evolved to be long and elongated structures and unlike Humans they are not totally encased with enamel.
A horse’s tooth has a layer of Cementum covering the tooth, grinding wears this softer structure of the teeth, the cementum and dentin and tends to leave the hard enamel which forms sharp folds called Enamel Occlusal Ridges. These rings form a self-sharpening function that helps to grind and break down the fibrous cellulose before swallowing which decreases the surface area available for the efficient bacterial breakdown and digestion in the hindgut. If the horse’s teeth are worn smooth or rasped excessively by a dentist, this can lead to feed and grain not being utilised or digested properly as it will be impossible for the horse to break down the forage into small enough pieces.
So, a horse’s teeth are designed to slowly wear away throughout its life. An average sized horse can have a 10cm tooth when young and this gradually wears away at the rate of around 2-3mm/year.
In an old horse, once the teeth have mostly worn away, they are referred to as a ‘smooth mouth’, this means the horse has worn down all the enamel in the tooth structure and will not be able to digest cellulose at all. The forage will not be broken down into small enough pieces for the hindgut bacteria to effectively digest it.
Horses grinding teeth are spaced wider apart on the top jaw and are designed to have a sideways and circular grinding motion. Hay and fibrous forage are chewed in large jaw sweeps to break it down. In comparison, when a horse’s diet is largely made up of concentrates or cube material, the jaw sweep will become more of a vertical chop and loses much of the large lateral sweep. This can lead to sharp edges developing on the sides of the teeth. This is why horses that are fed large amounts of concentrates will need their teeth attending to more regularly by the dentist.
For example, 1 kg of hay can take 3500-4500 chews/jaw sweeps and take 40 minutes, whereas 1kg of oats may only take 850 chews/jaw sweeps in 10 minutes. The oat chews will tend to be more vertical in sweep as they don’t require the same degree of pressure and motion to break down.
These functions of both the teeth and the digestive tract in the horse should help to explain why it’s important that we feed our horses in a biologically appropriate way. The foundation of the equine diet should always revolve around a high forage and fibrous diet in order to keep the animal as healthy as possible inside and out!
Also, the importance of quality, regular dentistry cannot be overstated. Your dentist will be able to monitor your horse’s teeth and make small adjustments where necessary, taking off sharp edges and keeping an eye on possible problems, infections and other damaged areas.