The Skin

The donkey typically has a long and dry coat and it is often difficult to see ectoparasites such as lice and ticks. Wounds may be missed and skin disease may be in the advanced stages before it is visible.

The long coat is also an important factor to consider when applying topical treatments as dispersal may not be as effective as in horses and ponies and the disease condition may not respond to the drug. Drugs applied as a pouron may not be effective in the donkey.

The donkey has evolved to live in an arid climate and its coat and skin have adapted to this environment.

Wet weather can cause problems for donkeys and they will usually seek shelter in wet or cold weather. Skin conditions may occur if shelter is not available. Rugs may be used in addition to shelter and may also be used in cold weather. The Donkey Sanctuary advises the use of donkey-shaped rugs.

The large ears of the donkey can result in significant heat loss in temperate climates, and prolonged wetting can predispose them to dermatophylosis. The ears can also be an obvious site for sarcoid development and fungal lesions.
 

CLINICAL EXAMINATION

The following points are important to consider when examining for conditions of the skin:

• palpate all areas as the longer coat can hide lesions, lumps and parasites
• assess the body condition score to check the long coat is not hiding weight loss
• skin disease presenting alongside weight loss may signify a systemic aetiology
• a full blood profile and adrenocorticotropic hormone (ACTH) testing is recommended in challenging cases because skin disease may be a sign of liver pathology
• the skin and coat changes apparent in the horse and pony as a result of pituitary pars intermedia dysfunction (PPID) may be less obvious in the donkey.

• the hair should be clipped over the area of any lesion so that the full extent and character of the lesion can be determined
• establish the size and characteristics of any tumours and check the whole animal because more than one lesion may be present
• observe and map the affected area because this can be very useful for assessing progress.
   

Relevant questions for the clinical history would include:

• are the donkey’s companions or handlers affected?
• have there been any changes to feed or environment?
• is there a previous history of skin disease and is it seasonal?
• are there any concerns over the systemic health of the donkey?
• has there been a history of ectoparasite infestation?
• are there any environmental factors such as low-lying water or wooded areas providing a suitable habitat for biting insects?
• what is the nutritional status?

Donkey diets may be deficient in vitamins and minerals, which can compromise skin health.

INFECTIOUS SKIN DISEASE

Dermatophytosis (ringworm) is diagnosed and treated as in horses and ponies, although the lesions may be much less obvious. Small alopecic patches may be the only sign. Widespread alopecia with crusting and excoriation may be present.

Remember the zoonotic implications of ringworm.

Histoplasmosis (Epizootic lymphangitis) and Cryptococcosis are found in donkeys. They are diagnosed and treated as in horses and ponies.

Bacterial infections, other than the above, are usually secondary. They are diagnosed and treated as in horses and ponies.

Viral infections, for example EHV3, coital exanthema, are found in the donkey. They are diagnosed and treated as in horses and ponies.
 

PARASITIC DISEASE

The donkey is affected by the same parasitic diseases as horses and ponies and these conditions are diagnosed and treated similarly.

Pediculosis is common in temperate climates. The long coat of the donkey will often hide the presence of lice until there is a heavy infestation. However, clinical presentation varies with individuals: some donkeys are seemingly unaffected by heavy burdens while small burdens result in intense self-trauma in others.

The treatment of lice infestation in the donkey is more successful if any long coat is clipped, allowing effective dispersal of topical treatment and better visibility of the site. Clipping can also increase exposure of the skin to UV light, which can be helpful.

It may be necessary to apply larger volumes of licensed topical preparations due to differences in the coat. It is important to note that drug resistance has been identified to some of the preparations licensed for equines.

It is worth establishing the type of louse present in a case before selecting treatment as this may determine whether topical or systemic treatment is appropriate.

• Amongst the UK Donkey Sanctuary herd the chewing louse, Bovicola (Werneckiella) ocellatus is prevalent and has been shown to be resistant to topical permethrins.
• In other donkey populations where chewing lice are present it may be appropriate to consider the use of topical permethrin.
• Systemic avermectin may be used where sucking lice have been identified.
• Topical application of fipronil has also proved efficacious in the treatment of lice infestations but clinicians must remember that larger volumes may be required to penetrate the donkey’s thick coat if clipping is not performed.
• The use of a topical 5% tea tree oil product has been shown to be an effective alternative to permethrin based compounds. One option is ‘Equine Nit Nat’ which was developed with The Donkey Sanctuary.

Flies and Midges (Culicoides spp) will have the same effect on donkeys as in horses and ponies. Fly-bite attacks occur predominantly on the distal limbs and in elderly/arthritic donkeys if these are less mobile. Hypersensitivity to fly bites or to Culicoides bites (Sweet Itch) will result in pruritic papules and nodule formation.

Flies can act as vectors for other disease such as habronemiasis.

Prevention of fly attack relies on good hygiene, the use of hoods and rugs and environmental measures, in the same way as is recognised for horses and ponies.
 

Pinworm Oxyuris equi infestation can be easily mistaken for Culicoides bites in donkeys. It frequently presents with hair breakage and excoriation of the rump, tail head and perianal region.

Mites infest donkeys in the same way as horses and ponies. Forage mites and Chorioptes spp may be seen and, rarely, the burrowing mites, Sarcoptes spp and Demodex spp. Donkeys fed and bedded on straw may have an increased likelihood of infestation with forage mites due to an increased exposure. They are often found around the head for this reason.

Ticks present problems as they are very difficult to find in the donkey coat. Donkeys are susceptible to tick-borne infections as in horses and ponies, for example piroplasmosis.

Habronemiasis and Onchocerciasis are found in donkeys. They are diagnosed and treated as in horses and ponies.
 

Ivermectin can be mixed with vaseline and used topically for habronemiasis in areas of the donkey that are problematic for treatment, such as the skin around the eye and the sheath. This will also protect the wound against flies during the period of treatment.

OTHER CONDITIONS

Sarcoids have been identified in the donkey and presentation and treatment is the same as in horses and ponies. 

• Early recognition and prompt treatment of a sarcoid facilitates the chance of successful therapy.
• Donkeys should be checked regularly, particularly the sheath and inguinal areas.
• Surgical or chemotherapeutic intervention, as in horses and ponies, remains the mainstay of therapy and laser or smart surgery with wide local margins are currently the most successful approaches.
• Multimodal therapy using surgery and adjunctive chemo or radiotherapy may be required.
• Specialist opinion should always be sought if there is any doubt over a treatment plan.
• Recurrence rates are high and owners and vets should be ever vigilant.
   

Other neoplastic diseases have been seen and should be considered as part of the differential diagnosis;

Melanoma appears to have a low incidence despite the high numbers of donkeys with a grey coloured coat.

Squamous Cell Carcinoma has been recorded in cutaneous, ocular and genital forms and should be investigated and treated as in horses and ponies.

Fibromas/fibrosarcoma have occasionally been diagnosed by histopathology in suspected sarcoid lesions. However, several authors consider these to be variants of the sarcoid and manage them as such.

Insect bite hypersensitivity is found in donkeys but it can be difficult to distinguish between hypersensitivity to the bite of Culicoides spp or to flybites. Hypersensitivity is diagnosed and treated as in horses and ponies.

Atopic dermatitis presents and is treated in the same way as in horse and ponies.

Vasculitis is rare in the donkey but when seen it should be treated in the same way as in horses and ponies. 

Autoimmune diseases have been recorded in the donkey, Pemphigus foliaceous being the most relevant. The prognosis is guarded.

Congenital diseases are rare in the donkey but junctional epidermal bullosa has been recorded.

Besnoitiosis may be seen as donkeys appear susceptible to the protozoal parasite Besnoitia bennetti.

Molluscum contagiosum, the pox virus, has recently been described in two donkeys.

WOUNDS

Approaches to the treatment and prevention of skin wounds in donkeys is the same as in horses and ponies.

Remember that donkeys may not be protected against tetanus and appropriate prophylactic treatment must be given.

Wounds may be advanced and possibly secondarily infected as the long coat of the donkey may hide wounds, and any grooming or examinations are often undertaken infrequently.

In working donkeys severe wounds can result from repetitive trauma arising from:

• poor tack
• carrying of inappropriate loads
• debilitated donkeys suffering from poor nutrition.

In these cases the cause of the wound has to be addressed in order to prevent re-occurrence. This may involve education and advice on alternative options for the owner or the community.

PREVENTION

The prevention of skin wounds is an important consideration. Owners should be advised to:

• vaccinate against tetanus
• undertake regular and thorough examination of the coat combined with daily grooming
• seek expert advice as soon as a problem is identified
• use correct and well-fitted equipment, especially harnesses and bits
• adapt tack to allow for any skin conditions or musculo-skeletal conditions, to minimise pressure sores or rubbing
• change or adapt management and working practices that contribute to the development of wounds.