Miniatures, Mammoths and Mules

MINIATURE DONKEYS AND MULES

Evidence suggests that miniature breed types became recognised between 1850 and 1970. Dentition evolution however, may take thousands of years and so it’s feasible that miniaturisation in just a few generations could present a mismatch in terms of developing standard sized dentition within a much smaller cavity. Interestingly, humans show a reduction in jaw size, which is occurring more rapidly than the 1% decrease in the size of our teeth, which occurs every 1000–2000 years. The result is a high prevalence of impacted wisdom teeth (72% of adults) and dental overcrowding.

While the evidence suggests that congenital dental abnormalities occur less than developmental anomalies, miniature equids are more prone to specific orodental abnormalities.

Miniature donkeys and mules must not be thought of as dwarfs. Dwarfism presents an undesirable, proportionate or disproportionate genetic state and is a significant risk in mini breeds.

There are no minimum height restrictions currently, but typically, minis are considered to be proportionally correct animals under circa 36 inches tall. A height of 38 inches is considered acceptable, but less desirable, and 40 inches and over is noted as the cross over with the standard breeds.

Incisors

The most frequently described malocclusion of the miniature donkey and mule is prognathism. Prognathia (or undershot jaw) is a class III malocclusion whereby the affected equids either demonstrate a lengthening of the mandible or a shorting of the maxilla, resulting in a lower incisor or mandibular protrusion. This conformational defect is typically visible from birth and may become worse (especially in the absence of appropriate treatment) with age. Accordingly, if the patient is to achieve any degree of improvement or resolution then a detailed oral examination of the mini foal is indicated. Class II and/or III dental malocclusion treatment in young stock may include the application of an ethically contentious orthodontic apparatus and/or significant surgical procedures typically alongside more regular dental equilibration.

Dental displacements and disparities in tooth number

Miniature donkeys and mules demonstrate a higher occurrence of dental displacements as the crowns shift, rotate and contort around each other during development and in order to erupt.

If unrecognised or untreated, displacements commonly lead to periodontal disease, diastemata, malocclusions, dysmastication, dental overgrowths, soft and/or hard tissue injury, periapical disease, and sinus disease (this list is not exhaustive). The self-perpetuating nature of dental disease generally indicates that the more severe pathologies occur in older patients. Throughout their lifetime, but perhaps most noticeable in younger equids, the mandible and maxilla remodel to accommodate the reserve crowns. The three caudal most maxillary molars develop their apices in close proximity to the rostral and caudal maxillary sinuses. Overcrowding of the dental apices however, may lead to an obstruction of drainage, in turn leading to nasal discharge. Additionally, epiphora is common in proportionally correct minis due to the presence of normal eruption cysts impinging upon the nasolacrimal canal.

Other consequences of overcrowding include the development of life limiting (and quality of life limiting) dental over-growths and periodontal disease. In some cases, and it is a best-case scenario for minis, some of the adult teeth may fail to develop altogether (known as oligodontia), this then provides more room for the remaining dentition to erupt freely and in correct alignment.

Oligodontia however, may fail to be uniform. Patients may present with one tooth missing from one arcade, but a normal number of crowns present in the occluding cheek teeth row. This presentation requires very regular and careful management of the unoccluded crown(s) to avoid penetration of soft or hard tissues/structures. Such cases are usually, but not always, terminal.

Conversely, miniatures may present with varying severities of polyodontia (supernumerary teeth) resulting in dental displacements and associated pathology.

Retained deciduous caps

The oral cavity is very dynamic in equids less than 5 years of age. Deciduous teeth are beginning to be replaced by permanent dentition from around the age of 2 years old. It is around this time when the foundations for future, long-term oral health are laid.

Deciduous cap retention may cause permanent crowns to displace, or develop a tooth root/apical infection. In minis where the dental arcades may be very compressed, the retention of milk teeth is so common it is almost routine. Oral assessments are therefore an essential element of health management during this time (usually 6 monthly). Cap retention is further confounded in cases with displacements, which may block the caps and prevent exfoliation.

The dilemma of miniature donkey and mule dental disease, seldom presents with just one disorder such as a singular displaced tooth. Left untreated, the displaced tooth invites a cascade of oral and digestive/systemic sequelae. Despite their often generous body condition scores, dental disease is self-perpetuating. This can start as a small and insignificant issue, but can develop over time into ever increasing degrees of pathology which may render the animal inappetant (leading to hyperlipaemia), or may cause such profound disease and trauma that recovery may not be possible.

MAMMOTH DONKEYS AND SPECIALIST LARGE BREEDS

Some larger and rarer breeds of donkey, including the Poitou, Zamorano- Leonés and Mirandês Donkeys (and similar European breeds) share several similar dental traits.

The physical size of the head will on occasion be large enough for professionals to use the longest standard extensions available for motorised hand pieces and still struggle to reach the caudal most regions. Unsedated routine dental examination and treatment is usually a joy to perform, in the poorly trained large or mammoth donkey however, professionals are likely to struggle significantly. Given the size and therefore weight of the head in these cases, it is essential for professionals to have some method of humane head support in place when working with patients under sedation.

Recent studies demonstrate a 2.25% prevalence of polyodontia in two rare breeds of large donkey in Portugal, 97% of which occur in the maxillary cheek teeth and were mostly bilateral distomolars. Accordingly, in all cases regardless of size, professionals should routinely count all of the visible crowns during examination.

It is very common for the Poitou donkeys to present with relatively shallow clinical crown. Periodontal disease and diastemata in these cases may be severe and elicit marked pain responses.

Gingival hyperplasia has been commonly found throughout the entire arcades, particularly in the larger French breeds of donkey. This is in addition to a tendency to develop shear mouth. In cases with both shallow clinical crown and shear mouth, it is often not possible to achieve improvements to the angulation of the occlusal surfaces as would be similar to those in equids with normal clinical crown height, as often there is minimal dental tissue above the gingiva.

Other common presentations of large donkey breeds in general include brachygnathia, ventral curvature of the incisors, retained deciduous teeth and dental displacements (linked with polyodontia in some cases) in addition to the routine observation of sharp enamel points and focal overgrowths.

In mammoth donkeys, it is not unusual for the incisors to erupt without the mesial compression required for a tight dental arcade, the crowns (deciduous and permanent) may erupt with significantly enlarged interproximal spaces, which may fail to improve with age. Mammoths also demonstrate a tendency for deciduous cap retention and generally slower dental maturation (by up to around 1 year).

HANDLING AND PHARMACOLOGICAL CONSIDERATIONS SPECIFIC TO MULES

It should be noted that being a mixture of horse and donkey behaviour, mules tend to show the behavioural traits of both parents. This means that their behaviour is likely to fluctuate between the nervous obviously fearful behaviour of their horse mother and more stoic nature of their donkey father.

Handling

Mules are likely to offer rapidly changing behavioural responses to different moments of their interaction with any equine professional.

They may initially start out nervous and fearful, then appearing more stoic as the interaction progresses and finally if pushed beyond their threshold, they revert to the nervous flight behaviour so commonly seen in horses.

It is this switching of behaviour between the flight and fight responses that can be so confusing for those people working with a mule. This switching is even more prevalent if the mule has not been previously well handled.

Pharmacological considerations

When treating mules, depending on the temperament of the mule and procedure to be performed, the dosages for sedation may need to be increased by 30–50% above that given to donkeys.