by Emanuela Valle, veterinary, Prof.at Torino University
There are generally 40 teeth in the mouth of an adult horse. The so-called dental formula for each hemi-arch includes: 3 upper and 3 lower incisors, 1 canine above and one below, 3 premolars above and 3 below and finally an equal number of molars. The total, multiplied by 2, gives the result of 40 teeth. While this is the standard number for male horses, it can be more variable in mares. In fact, mares generally do not have canines and therefore they have 36 teeth. If canines are present, the mare is called in jargon “staggered”. It must also be said that a variable number of horses, between 20 and 30% have got the so-called "lupins" or wolf teeth. They are small teeth that correspond to the vestigial residue of the first premolar and are mainly located at the upper jaw level known as the maxillary arch, but are very rare in the lower jaw known as the lower mandibular. If they are present, the number of teeth in male horses can therefore rise to 42 and in mares 38.
The teeth of the adult horse, unlike those of humans, continuously grow by 1-1.5 mm per year. This continuous growth of the tooth, which gradually wears out, stops at around 20-23 years of age. In fact there is no precise moment, but the growth of the tooth ends at variable periods thus making chewing for the horse less efficient. Once the growth of the tooth stops and the tooth is all consumed, the horse begins to have problems chewing especially the forage and must therefore be monitored carefully in order to avoid excessive weight loss. Horse teeth are defined as:
• Hypsodont: they are teeth with an almost continuous growth that lasts until old age, when the growth of the tooth ends. In practice, during the life of the horse, the tooth grows slowly, while the continuous chewing of the forage consumes the tooth slowly.
• Anisognathus: the teeth do not match perfectly, as the upper maxillary arch is about 30% larger than the lower mandibular one. This particularity, together with the chewing angle of the surface of the teeth, allows a particular chewing defined as laterolateral which allows the fibrous food to be crushed in order to create fragments of chopped food that can be attacked by digestive enzymes.
• Dipiodon: they are milk teeth which are then replaced by definitive or permanent teeth.
The rule of six: to remember when the milk incisors emerge, use the rule of 6 days for the incisors, 6 weeks for the medians and 6 months for the cantins. These times are indicative because from subject to subject there may be physiological variations of the moment in which the teeth erupt.
Each hay chew cycle includes approximately one chew per second. Generally, the horse takes 8-10 chews for each mouthful before moving on to the next. A horse that chews well in fact has a rhythmic and constant chewing action. This means that the healthy adult horse performs 3,500 to 3,800 chewing acts in an hour, which is the time it takes to take about 1.5-1.8 kg of first cut hay. This depends on the age of the subject and its voracity. In fact, there are more voracious horses that at the same time chew more quickly reaching even 11 chewing acts in 10 seconds, while others are slower and more moderate. This could not only be due to the horse's personality but also to characteristics of the morphology of the head, such as the width of the mouth and the dental table. For example, some pony breeds can even perform 67-70 chewing acts per minute.
Ponies are naturally more voracious and chew a lot more per minute. This means that they can eat larger quantities of food in the same unit of time. The state of wear of the teeth and the frequency of veterinary checks (in particular the trimming of the dental table) influence the chewing of the horse. In fact, a horse with dental tips, which can create pain and discomfort when chewing, compensates for this problem by increasing the number of chews per minute for the same mouthful of forage. This causes it to produce the so-called “butts” or boluses of fodder that fall from the mouth after partial chewing and soaking with saliva.
Looking for food and chewing is a real job for the horse that keeps it busy and allows it to produce the essential saliva to lubricate the food, but also to buffer the acidity of the stomach, thanks to its bicarbonate content. If for 1 kg of hay an adult and healthy horse, weighing about 550 kg, produces about 4-5 liters of saliva, it can be assumed that for an hour of consumption of the same food, it produces about 6 liters, consuming approximately one kilo and a half of hay or a little more. The characteristics of the dental table, together with the prolonged chewing, make us understand that the horse's teeth require special attention: they must be checked periodically not only in the elderly horse but in all horses. The most typical problem is that of the formation of the so-called enamel points, which are formed on the outer edge of the premolars and upper molars and the inner edge of the lower teeth. This is because the chewing movement, of the latero-lateral type, describes the shape of a pot-bellied eight following the oscillation of the mandible on the jaw: in this way the horse obtains a grinding effect that finely processes the food. If not properly leveled, the tips of enamel are annoying for the horse: they can injure the mucosa especially in the posterior portions of the cheek or tongue. The cuts can then ulcerate, creating a lot of pain. Unfortunately, being very far down the oral cavity, they are not visible at the simple opening of the horse's mouth, so for an appropriate check of the mouth it is necessary to call our trusted veterinarian who uses a mouth opener to better check the presence of any problems. The teeth check should be done on an annual basis: shorter or longer times can be decided according to the advice of the treating veterinarian. To keep chewing healthy, in addition to carrying out regular dental checks it is a good idea to set a diet based on fiber. If it is not possible to guarantee grazing on suitable meadows for the horse, it is good to provide forage such as hay. Generally a good diet must include shares of first cut hay around 2% of the animal's weight, say 10-10.5 kg per day for a 550 kg horse, possibly associated with other foods according to it’s specific energy needs and its requirements. The hay must be of good quality and well distributed throughout the day. However, the possibility of spending a few hours in the paddock must always be associated with this: if there is little grass, we leave a few portions of hay available. After a few runs and bucking it will surely start nibbling and enjoying the effect of the freedom of the paddock.
Ideally, the horse should be handled in a group with it’s peers and in large spaces where it can graze. If this is not possible due to lack of adequate space, the hay administered must be of good quality and well distributed throughout the day. However, the possibility of spending a few hours in the paddock together with the other horses must always be associated with this. If there is little grass, let the horse have a few slices of hay available: after a few runs and bucking it will surely start nibbling and enjoying the feeling of freedom.
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