The Foot

The donkey’s foot has several significant anatomical differences to that of the horse and pony and it is important to be aware of them.

• A more upright hoof-pastern axis.

• A dorsal hoof wall that is 5 to 10 degrees more upright.

• A broader frog with an apex that does not extend as far towards the toe.

• A U-shaped sole slightly flared at the heels.

• Narrower heels resulting in a cylindrical shaped hoof capsule.

• A thicker sole.

• A constant hoof-wall thickness from heel to toe.

• An extensor process of the distal phalanx which is located distal to the upper limit of the hoof capsule in normal feet – lateral radiographs should be interpreted accordingly.

• Microscopic differences in horn tubule size, density and distribution patterns.

Studies on donkeys kept in the UK indicated that moisture content of the hoof wall, a major factor in determining its mechanical properties, is significantly higher in donkeys than in horses and ponies, making it more pliant and deformable. This may predispose to hoof capsule disorders and pathological conditions when animals are kept in environments with higher humidity.

The donkey foot has a distinctive five-point loading pattern with focal stresses acting at the dorsal aspect of the hoof, the quarters and the heels, in contrast to the four-point pattern reported in the horse and pony.
 

FARRIERY OF THE DONKEY FOOT

Depending on the environment and lifestyle, a donkey’s feet will generally require trimming every six to ten weeks. Even where donkeys are walking on surfaces that naturally abrade hoof growth, it is recommended that this regular check and trim is not ignored.

Trimming

The limbs should be kept low when trimming and should not be abducted from the body. This will reduce the risk of unbalancing the donkey or causing pain and discomfort in animals that are affected with arthritis. It will also facilitate compliance.
 

When trimming it is important to note donkey-specific differences and adjust accordingly:

• Pare the sole first, removing all loose and necrotic material and paring back any overgrown frog. The frog frequently becomes large and bulbous, with the grooves and sulci retaining foreign matter and infection. The frog should be trimmed to a neat triangular shape, removing all degenerate and overgrown tissue.

• The sole of the donkey does not tend to flake away naturally, unlike the sole of the horse and pony. Consequently it frequently requires paring back so that it ideally becomes concave, minimizing the area of sole that will be in contact with the ground and enabling the walls to bear weight. The sole is pared back in increments until thumb pressure between the apex of the frog and the toe causes the sole to yield perceptibly.

• Trim the wall guided by the pastern axis and the angle of the wall at the proximal midline. A straight hoof pastern axis is ideal, with heel height frequently requiring reduction. The well-developed coronary band in some donkeys can be deceptive when assessing the hoof pastern axis. Excessive rasping of the hoof wall should be avoided.

• Assess the medio-lateral balance as in the horse and pony, and make adjustments so that the weight is transmitted equally across the width of the foot.

• Assess the balance, gait and comfort of the donkey post-trimming.
   

Shoeing

For most activities and in most situations donkeys do not need to be fitted with shoes. When wear is excessive and shoes are required, greater care is needed when placing nails in the narrow upright walls of the donkey hoof.

Many traditional donkey shoes limit or prevent heel expansion. These are not recommended as they restrict the natural functioning of the hoof and may predispose to longer-term problems such as atrophy of the frog and broken forward hoof pastern axes.
 

Synthetic shoes that cover the entire solar surface predispose to degeneration and disease of the sole and frog. These should also be avoided.

In cases where it is necessary to relieve sole pressure (e.g. cases of chronic laminitis with thin soles) or where rebuilding the hoof wall after remedial farriery or surgery, hoof resins and thermoplastic granule products have proven useful. They are used in the same way as with horses and ponies. Ensure that feet are clean and dry for the products to work effectively, and apply in thin layers to avoid tissue damage due to the heat generated when the products harden.
 

CLINICAL EXAMINATION

Donkeys experiencing pain tend to stand still or lie down, hence identification of any lameness or the presence of pain may be difficult and is often delayed.

Hyperlipaemia may occur in association with any painful or movement- limiting foot disease. A full clinical examination is therefore strongly recommended when clinicians are presented with a lame donkey.

It can be challenging to examine donkeys for mild lameness because they rarely trot or move at speed when led and they often mask evidence of pain in the presence of others. In many cases the only way of assessing a donkey’s gait is to spend time observing their movements in their natural environment. Owners may also report subtle changes in behavior, including reduced activity or increasing periods of time spent laying down.

Hoof testers may be useful in localizing or identifying foot pain, although the results should be interpreted with caution in these stoic animals.

As with horses and ponies, assessing digital pulse intensity is a key part of a lameness examination in the donkey.

During examination of the foot, keep hooves close to the ground to minimize stress on the joints and reduce discomfort in older or arthritic donkeys. Foot trimming may aid effective examination of the foot.

A mildly toe-out conformation can be normal in donkeys, but may make assessing mediolateral imbalance more challenging. Radiographs are useful to determine whether corrective trimming for balance is necessary.

Radiography

It is important to note that there are certain key differences in the donkey’s foot compared to that of a horse or pony.

• A limited broken forward hoof pastern axis can be considered normal, with a degree of rotation of the dorsal aspect of the distal phalanx in relation to the long axis of the proximal phalanx.

• The distal phalanx is positioned more distally within the hoof capsule resulting in a greater distance between the proximal limit of the hoof wall and the extensor process of the distal phalanx (‘founder distance’). The mean founder distance in the standard donkey is reported as 10.4mm (SD +/- 3.66).

• The mean integument depth measured at the midpoint of the distal phalanx is 25% greater in the donkey (16.2mm) than reported in the pony.

In ideal situations, the donkey foot displays a parallel relationship between the dorsal hoof wall and the dorsal border of the distal phalanx in the same way as the horse and pony. However, in donkeys where regular foot care is neglected this is not always the case.

The angle of the solar surface to the ground is similar to that reported for the horse and pony.

COMMON CONDITIONS

The overgrown hoof

Overgrown hooves, with or without twisting, is a common problem in donkeys. In extreme cases hooves can resemble ‘Turkish slippers’. However, many less pronounced cases of overgrowth, with painful stress on joints and ligaments, are all too frequently seen.

Lateral radiographs will aid trimming, and allow an accurate position of the distal phalanx to be established and an assessment of any laminitic change to be made. In the absence of radiographs, successful trimming can be undertaken if the position of the distal phalanx is estimated from its relationship to the coronary band, bearing in mind that the proximal extensor process will be distal to the coronary band. This distance may be greater in cases of chronic laminitis, a common problem associated with overgrowth.
 

Recommendations for correction are:

• remove the frog and sole overgrowth and reduce the heels first, in order to allow the bearing surface to sit correctly on the ground

• remove toe overgrowth, stopping paring when thumb pressure on the sole reveals a slight ‘give’

• dress back the dorsal wall of the hoof with a rasp once the toe has been removed, guided by the angle of the proximal hoof wall adjacent to the mid coronary band

• remove degenerate hoof wall and white line if enough wall remains to allow the donkey to move reasonably comfortably.

Pay careful attention to post-trimming analgesia. A comfortable, deeply- bedded stable, good hoof hygiene, regular inspection and an appropriate farriery plan for the future should all be considered.
 

Laminitis

Laminitis is one of the most common causes of lameness in non-working donkeys. It is often undetected until the condition is advanced. This is possibly due to the stoic nature and non-athletic lifestyle of many donkeys and to the subtlety of a donkey’s change in behavior in response to pain.

Donkeys with laminitis may present with reluctance to move, a shortened stride, increased time spent recumbent and weight shifting on hard ground. They are less likely to show the classical equine laminitic stance unless severely affected.

On examination, laminitic donkeys may show evidence of increased digital pulses and solar pain that may be localized to an area corresponding to the tip of the distal phalanx, just in front of the frog. In chronic cases, distortion of the hoof capsule may be present and donkeys may develop muscle wastage around the shoulders.
 

Diagnosis is made on clinical signs and radiographic changes seen on lateromedial radiographs of the affected feet, taking into account the different parameters for normal donkeys. In view of the founder distance in normal donkeys it can be difficult to assess any depression around the coronary band. However, donkeys with laminitis may exhibit pain associated with palpation of this region. Cases of chronic laminitis can be difficult to assess and radiographs are an essential part of making a diagnosis. Typical changes to the distal phalanx include modelling or lipping of the tip, demineralization of the distal margin and distal displacement within the hoof capsule.

Radiographic changes in the laminitic foot of the adult donkey (Collins et al, 2011):

The aetiology of laminitis in donkeys is similar to that in the horse and pony. Equine metabolic syndrome (EMS) and pituitary pars intermedia dysfunction (PPID) become more significant in elderly and obese animals, and are increasingly recognised as an important factor in the aetiology of laminitis in the donkey.

Treatment for laminitis in donkeys is similar to treatment in the horse and pony.

Dietary management is essential to control weight, although care needs to be taken with weight loss to ensure that it is not excessive, because this may increase the risk of hyperlipaemia.

Medical management of laminitis in the donkey is similar to that in the horse and pony, although the frequency of dosing for most NSAIDs is different due to differences in drug metabolism when compared to horses and ponies.

When an animal is in acute pain, multimodal analgesia can be helpful using similar doses of paracetamol, opioids and ketamine to those administered to horses and ponies. Fentanyl patches have also been used on donkeys.

Corrective farriery is important for rebalancing the foot once the acute phase is over.
 

Lateromedial radiographs are useful to guide farriery. The frog of the donkey, although often well developed, tends not to extend as far forwards towards the toe as in the horse and pony. Pedal bone support by frog supports alone is therefore not helpful and possibly contraindicated. A thick cotton pad covering the whole foot, together with deep bedding, can provide support and comfort. Hoof resins and thermoplastic granule products have proven useful to create shoes and provide protection, but care must be taken in active cases as the heat generated when the product hardens may increase inflammation or pain. It is therefore most useful in cases of chronic laminitis.

After the acute phase, exercise can also be beneficial to control weight and provide enrichment.

White line disease

Donkeys appear to be prone to white line disease in some environments and dirty, wet conditions, genetic factors, mechanical stress and poor farriery are cited as causes. Lesions can extend around the circumference of the hoof and progress proximally towards the coronary band.

Donkey hooves have a higher moisture content in certain environments than horse and pony hooves, which may exacerbate the problem. Repeated bouts of laminitis weaken the sole-wall junction, providing an ideal route for keratolytic fungi and bacteria to invade.

The condition is characterised by crumbly grey or white material at the sole-wall junction. Donkeys with white line disease are not usually lame, although in severe cases deep pockets of black, foul-smelling discharge may be associated with lameness and sensitivity to hoof testers.

Treatment is aimed at debriding all affected horn, rebalancing the foot and providing a dry, clean environment. Donkeys can cope with extensive debridement around the toe, but radiographs are advised where concurrent signs of chronic laminitis and thin soles are seen.
 

White line abscess

White line abcesses can be very frustrating to deal with in donkeys because there is rarely an obvious lesion, and many hooves have stretched white lines and multiple areas of white line disease to explore. It may be possible to localize the abscess in small, lightweight donkeys if hoof testers are used. However, some larger, thick-soled breeds such as Poitous show little response to the hoof tester.

Thorough initial trimming of the hoof is recommended. Remove all but the deeper lesions. Difficult cases can benefit from a bilateral abaxial sesamoid nerve block to aid comfort during resection.

Pus may move more dorsally in longstanding cases, or inwards towards the pedal bone. Pus rarely underruns the sole in donkeys. Pus can be encouraged to drain by poulticing and immersing the foot in warm water for 5-10 minutes several times a day. Radiographs are indicated if pus has not drained and the donkey has been severely lame for more than two days. In cases where the abscess has reached the pedal bone leading to osteitis, surgery may be necessary to curette the bone and remove the infected tissue.

Tetanus prophylaxis must be considered and adequate analgesia provided to maintain comfort and promote appetite. Lame donkeys should always be monitored for appetite and signs of hyperlipaemia.

Chronic foot disease

Chronic foot disease is a descriptive term used to categorise cases with any combination of chronic laminitis, white line disease, pedal bone degeneration and chronic pain. It may be possible to keep such cases comfortable with the long-term use of NSAIDs, careful farriery, level pastures and soft bedding. It is essential that the quality of life of affected donkeys is regularly assessed. Objective recording of assessments over time is very useful in helping to decide when euthanasia is appropriate.

These cases respond poorly to stress and the increased weight-bearing associated with transportation. Clinicians should therefore be particularly careful when assessing the fitness to travel of such donkeys.

Keratomas

Keratomas are seen in donkeys, affecting both front and hind feet. Clinical signs include repeat abscess-like lameness with pus frequently discharging from the coronary band or sole. In some cases there is associated deformation of the hoof wall.

Dorsoproximal-palmarodistal oblique radiographs will reveal a smooth defect in the margin of the distal phalanx. Surgical removal is required but recurrence can be an issue.

PREVENTION

The prevention of hoof disorders relies on the following throughout the life of the donkey:

• appropriate nutrition and maintenance of a healthy body condition score

• regular foot care and farriery appropriate to the specific needs of the donkey

• a dry, clean environment, including stabling and exercise area

• prompt attention as soon as signs of lameness are seen.