DS research

There are significant numbers of donkeys kept as companion animals, both in the UK and abroad. Like their horse and pony compatriots, many kept donkeys are geriatric. Additionally, obesity is a common problem, irrespective of age. Diagnosis and management of endocrine disease in donkeys is challenging as many of the available tests for horses have not been specifically validated in donkeys. Furthermore, endocrinopathic laminitis in the donkey is not infrequently subclinical. The term ‘subclinical,’ is perhaps inappropriate, for the lack of clinical signs may not correlate with the severity of the laminitis episode but instead be a feature of the donkey’s notoriously stoic behaviour with respect to pain.

As a species, the donkey has evolved to be extremely energy efficient, with an inherent ability to maintain good body condition on lower energy diets. They have a slower intestinal transit time and greater efficiency of fibre digestion than the horse [1]. Donkeys appear able to accumulate adipose tissue with ease. Whilst these innate traits serve the working donkey or those kept in harsh environments where food resources are scarce well, they predispose the sedentary donkey to obesity, dyslipidaemias, insulin dysregulation and other metabolic disorders.

Donkey, or asinine, metabolic syndrome is increasingly recognised by equine veterinary practitioners. Clear and precise definitions are lacking and currently rely on extrapolations from equine metabolic syndrome. The clinician presented with an obese donkey should be suspicious of underlying metabolic derangements. The donkey may be generally obese, or have defined regional adiposity, with deposits along the neck, dorsum and rump being common. There are usually substantial subcutaneous fat deposits on the ventral abdomen in obese donkeys. Awareness of the obese donkey may only arise when the otherwise healthy donkey is presented for routine preventative care, such as vaccination or dental care. This provides an ideal opportunity to discuss the donkey’s body condition and diet, with the intention to reduce development of metabolic disease. Initial clinical assessment must include an evaluation of any indicators of laminitis, whether subtle or overt. The donkey that is described as unwilling to walk may actually be in discomfort rather than being unused to handling. It is imperative that provided diets are appropriate for the donkey’s life stage. For the adult, healthy donkey, with good molar function, the majority of forage intake should be provided by straw, with hay/haylage or restricted grazing making up the remainder of the diet. Owners should be advised to aim for straw to provide 75% of intake in summer and 50% in winter. Supplementation with a vitamin and mineral balancer is recommended. The conscientious owner may be willing to have their forage sugar content analysed, to further guide dietary management.

If a donkey remains obese, despite sufficient time and appropriate diet for expected weight loss to ensue, further investigation for metabolic disease should be undertaken. Basal insulin concentrations may be elevated in obese donkeys. The established reference range at The Donkey Sanctuary for a non-fasted insulin sample in the adult donkey is 0-15.1 uIU/ml (TOSOH AIA, using two-site immunoenzymometric serum assay). As for horses, a normal insulin concentration does not rule out insulin dysregulation and dynamic tests are recommended for further investigation. Protocols have been developed for donkeys, with intravenous glucose tolerance test, combined glucose-insulin test and oral glucose tolerance tests described in the literature [2] but insulin cut-off values for these tests have not been validated for donkeys. In the author’s clinic, the oral glucose tolerance test with corn syrup is used as this provides an accessible and practical dynamic test. The major limitation being that the protocol used is that developed for horses and may not be directly transferable to donkeys and, again, there is no validated insulin cut-off value. Consequently, diagnosis of asinine metabolic syndrome is currently made based upon combinations of clinical observations, poor weight loss despite appropriate diet, evidence of hyperinsulinaemia or insulin dysregulation and history of laminitis episodes.

Management of asinine metabolic syndrome is as challenging as the diagnosis. Many owners struggle to appropriately diet their donkey, particularly if any companion is not obese and/or has different dietary requirements. It is now widely understood that donkeys form strong bonds with their companions and can become distressed and at risk of hyperlipaemia if separated. However, for short periods if one donkey needs supplementary feed companions can be kept in sight of each other, yet physically separated by a fence or stable door. Owners should also try to encourage their donkeys to exercise, which is admittedly no mean feat. Turn out onto a bare pasture, which donkeys can explore and exercise within, is likely to carry more benefit than stabling a donkey away from rich grass pastures. If a donkey is accepting of a head collar and being led, many owners enjoy taking their animals for short walks. Providing enrichment activities that encourage the donkey to be mobile and explore are also helpful.

It goes without saying that exercise should not be advised until active laminitis has been ruled out. An association between obesity, insulin dysregulation and recurrent laminitis in donkeys has been reported but in a recent cross-sectional study of 707 donkeys in the UK [3], the presence of basal hyperinsulinaemia or PPID (indicated by seasonally adjusted elevations in ACTH) was not associated with increased odds of laminitis. However, this study acknowledged the lack of validated dynamic testing for either PPID or AMS and the potential errors in classification of cases. In the absence of definitive knowledge, clinicians should err on the side of caution and be alert to the potential for endocrinopathic laminitis. Management of laminitis in the donkey has been covered elsewhere [4].

The use of medication to treat asinine metabolic syndrome has not been extensively evaluated. As for horses, therapeutic protocols should only be used as an adjunct to dietary and exercise management. The use of levothyroxine in the donkey at standard equine doses has been reported [2]. Studies are needed to assess the safety and efficacy of ertugliflozin in the donkey, alongside any other medication proposed for treatment of metabolic syndrome in the horse.

References:

[1] Thiemann AK, Sullivan RJE. (2019). Gastrointestinal Disorders of Donkeys and Mules. Vet Clin North Am Equine Pract 35(3):419-432

[2] Mendoza FJ, Toribio RE, Perez-Ecija A. (2019) Metabolic and Endocrine Disorders in Donkeys. Vet Clin North Am Equine Pract 35(3):399-417

[3] Menzies-Gow NJ, Wakeel F, Little H, Buil J, Rickards K. (2021). Cross-sectional study to identify the prevalence of and factors associated with laminitis in UK donkeys. Equine Vet J. 54(4):757-765

[4] Thiemann A.K, Buil J, Rickards K, Sullivan R.J (2021). A review of laminitis in the donkey. Equine Vet Educ 34(10): 553-560

Colitis and typhlitis are diagnosed in donkey populations. Precise clinical presentations vary, depending on whether acute or chronic, a single individual or a number of animals in a group outbreak situation. The common feature, irrespective of circumstance, is that of a dull donkey and consequently, in the initial stages can be challenging to differentiate from the many other potential causes of dullness. Typically, donkeys present as inappetent, or only picking at feed, behaviour is depressed and they may distance themselves from companions. It is vital that owners and vets are aware that this likely constitutes a medical emergency and a clinical exam should be performed without delay. In acute cases, the donkey may be tachycardic, tachypnoeic, pyrexic, have congested mucous membranes with delayed capillary refill time and significantly reduced borborygmi. However, many cases can initially present with relatively normal parameters, yet progress to a peracute presentation and become moribund within hours. A salient point is the lack of diarrhoea in most donkeys with colitis. Ventral or limb oedema is not a consistent finding. Overt demonstrations of abdominal pain, such as rolling or kicking at the abdomen are uncommon in donkeys but if present are likely to indicate severe pain.

Thorough history taking is essential to guide diagnosis. Risk factors for colitis in donkeys include stressors such as recent movement, management or dietary change, alongside ingestion of toxic feed substances, infectious aetiologies, endoparasite infestation and recent anthelmintic or antimicrobial use. Right dorsal colitis does not appear to be common in donkeys, irrespective of short or long-term NSAID treatment at standard maintenance doses. Dysbiosis, secondary to any of the previously listed stressors, may be a significant factor in the development of colitis. Toxic and infectious causes are higher up the differential list in an outbreak situation. In chronic cases, insidious weight loss may be noted and intermittent episodes of dullness and colic.

Common differentials include hyperlipaemia, hepatopathies, other forms of colic including impaction or sand and any systemic inflammatory process causing pain and discomfort. Co-morbidities of any of these with typhlocolitis are not uncommon and can complicate diagnosis and treatment.

In addition to the basic clinical exam, vets should perform a rectal examination where possible. The aim is two-fold – to establish the presence of intestinal distension, displacement or impaction and to obtain a faecal sample for subsequent analysis. Testing for Salmonella, C.difficile and C.perfringens (including toxins) and Coronavirus alongside worm egg counts are recommended. Additional tests may be advised for foals. A blood sample should be obtained for routine biochemistry and haematology alongside inflammatory markers and, essentially, serum triglyceride concentrations. Feed samples can be collected for analysis if ingested toxins are suspected. Passage of a nasogastric tube is useful to assess for the presence of reflux. Transcutaneous ultrasonographic abdominal examination is ideal for further assessment, including measurement of intestinal wall thickness but may not be available in the field. Owners should be counselled as to the guarded prognosis and potential costs involved. Referral to a clinic setting should be considered for donkeys in need of intensive care but the risks of stress induced by movement will need to be taken into account.

Initial treatment in an ambulatory setting and whilst awaiting results of initial diagnostics centres on stabilising the donkey, restoring fluid and energy deficits and relieving pain. Unless there is gastric reflux and/or complete ileus, if the donkey is not voluntarily eating, nasogastric intubation of a water/electrolyte combination (the average standard size donkey stomach will hold approximately 3 litres of fluid) with dextrose or glucose powder and oat-based cereal (fine milled porridge cereals) should be given. If an infectious or toxic aetiology is suspected, enteral adsorbants such as smectites may be given down the stomach tube. Severely hypovolemic donkeys, or those with total ileus may require intravenous fluid boluses in the field before being stable enough to transport to a clinic. Analgesia is essential, usually flunixin meglumine at 1.1mg/bwt BID i.v providing the donkey is sufficiently hydrated, otherwise anti-endotoxic doses can be given and/or paracetamol at 20-25mg/kg p.o BID. Alpha-2 agonists and opioids may be required for multimodal analgesia, again extrapolating from standard equine doses. Use of corticosteroids in the acute phase is often debated and should be subject to a risk benefit analysis -the merits of potent anti-inflammatory activity versus worsening of systemic infection for example. Decision making for administration of other medications, such as anthelmintics, antimicrobials, gastroprotectants, pro-kinetics and other anti-inflammatory and anti-endotoxin therapies follow the same rationale as for horses and there are no peer-reviewed donkey specific guidelines. In our Donkey Sanctuary population, post mortem data of non-survivors indicates that very sick donkeys with colitis may be predisposed to gastric glandular ulceration.

If the donkey is worsening or failing to respond to treatment and intensive care is an option then remember to hospitalise companions with the patient, to reduce further distress. As for horses, strict biosecurity measures should be adhered to until infectious causes can be ruled out. In a donkey with severe hypoalbuminaemia, colloid fluid therapy may be indicated. Severe mural oedema has been identified at post-mortem in the intestines of donkeys subjected to aggressive crystalloid therapy and this likely worsens ileus. Other conspicuous findings of non-survivors in our population at post-mortem have included focal or diffuse severe necrotisation and encysted cyathostome burdens

Vets and owners should establish clear end points for treatment, if the donkey is responding poorly. Repeated transabdominal ultrasound, blood work including lactate quantification and results of abdominocentesis may be used to guide decision making. There are donkey specific biochemical and haematology parameters [1] but normal intestinal wall thicknesses

and lactate reference ranges have not been established. For patients that are responding favourably, provision of their normal diet and good nursing care are essential for recovery. Like horses, donkey colitis patients may be prone to laminitis. Transfaunation using faeces from another donkey is a valid consideration in the recovering patient. Note that the donkey gut microbiome is not the same as that of the horse [2] and therefore horse-specific probiotics are unsuitable.

References:

[1] The Donkey Sanctuary (2020). Parameters for Haematology and Biochemistry. Available at: https://www.thedonkeysanctuary.org.uk/research/sites/uk/files/2020-02/parameters-for-haematology-and-biochemistry.pdf

[2] Edwards, J.E., Schennink, A., Burden, F. Long S., van Doorn D.A., Pellikaan W.F., Dijkstra J., Saccenti E., Smidt H.. (2020) Domesticated equine species and their derived hybrids differ in their fecal microbiota. Anim Microbiome 2(1):8

Clinicians familiar with anaesthetizing horses will find many basic similarities between the species, but knowledge of some of the differences with donkeys will ensure a better approach.

Laminitis is a relatively common, painful condition of donkeys, ponies and horses. The underlying principles of pathology, diagnosis and treatment are broadly similar, but there are features of donkey anatomy, behaviour and physiology that differ from the horse; understanding these will improve treatment outcomes (Thiemann et al, 2021).

A study of over 2500 donkeys in the UK, found a prevalence of 4% of donkeys presented with laminitis with 46% of cases acute and 54% chronic. This is likely to be an underestimate due to the high levels of obesity and poor detection of the disease.

Recognition of laminitis

Few donkeys in Europe work, most are companion equines. This often results in late detection of laminitis in this species. Typically, signs are subtle, and include altered posture, stiff or shuffling gait and lameness on turning. There may be increased digital pulses and pain to hoof testers. Many donkeys will just lie down, and some owners can misinterpret this as normal resting behaviour.

In chronic cases, there will be abnormal growth rings on the hoof, a flatter sole and, in severe cases upper limb muscle atrophy and flexor tendon breakdown.

Using the Donkey Facial and Donkey Composite pain score (Van Dierendock, et al 2020) enables clinicians to quantify donkey pain and monitor response to treatment and analgesia.

The anatomy of the donkey hoof varies from the horse- P3 sits further distal and there is typically 10mm “founder distance” as normal between the coronary band, and top of the extensor process. The frog tissue is further back on the distal border of P3, this makes use of a heart bar shoe inadvisable. A normal hoof should have at least 10mm sole depth. The external hoof wall is approximately 5° more upright than a horse, but the phalanges, pastern and dorsal hoof wall should align.

Radiographs of donkey hooves need interpreting using donkey parameters.

Obese donkeys suffer from Asinine Metabolic Syndrome (AMS) and donkeys with Body Condition Score >3 (scale 1-5) are at risk. Donkey specific BCS charts and weight nomograms are available (The Donkey Sanctuary, 2020a & 2020b) to assist with assessment. Basal insulin and karo lite testing can be used to confirm a diagnosis of AMS.

Elderly donkeys can develop PPID and, as in the horse, seasonally adjusted donkey specific reference ranges are available.

Treatment of laminitis

As in the horse, the basis of treatment consists of rest, analgesia, foot care and dietary adjustments. In the donkey acute pain and stress, or rapid change in diet may precipitate life- threatening hyperlipaemia (Burden et al, 2011). Ensure the donkey’s appetite and demeanour are closely monitored, and while it is appropriate to reduce the sugar content of any fibre being fed, a reduction in fibre or attempts to diet an obese donkey should be done in a gradual manner.

Donkeys metabolise all NSAIDs (except carprofen) faster than horses, and after a loading dose of 4.4mg/kg BID of phenylbutazone, long term use at 2.2mg/kg BID is considered safe with less risk of dorsal colon ulceration. Meloxicam has a short half- life in donkeys (6 hours) and there is little data on newer NSAIDS. Paracetamol is a useful adjunct at 20-25mg/kg BID. Miniature donkeys require TID dosing for adequate analgesia.

Digital hypothermia is well -tolerated by donkeys and can be useful in acute cases or as preventative in sepsis cases.

In acute cases foot support is best provided with a deep bed, and whole hoof padding or using a commercially available sole support.

Corrective farriery after an episode is an important part of rehabilitation of the hoof, and for chronic cases with flat soles the use of acrylic rim shoes may assist in providing comfort.

Medical support for underlying AMS or PPID is similar to in the horse. The Donkey Sanctuary has little experience yet with the use of levothyroxine to aid weight loss, or insulin lowering drugs such as ertuglifloxin. Pergolide for the reduction of ACTH is known to cause appetite suppression in some donkeys, so when used, the donkey needs careful monitoring.

Prevention of laminitis

Preventative medicine in donkeys is often poor (Barrio et al, 2020), and engaging with owners about correct nutrition, weight management and farrier care is a good strategy. The Donkey sanctuary provides an online resource “The Donkey Academy” with free courses for owners, vets and farriers to assist in this area, as well as fact sheets and handbooks: https://www.thedonkeysanctuary.org.uk/research/what-we-do/knowledge-and-advice/donkey-academy

Donkeys with good dentition cope well on a high fibre, low starch diet where straw provides the bulk of the forage, supplemented by a small amount of vitamin/mineral balancer (Burden et al, 2019). If dieting is needed, suitable mental stimulation helps with prevention of stereotypic behaviour developing (The Donkey Sanctuary, 2020c).

In many cases severe chronic laminitis is undetected and vets and owners can work together to understand the impact of this on Quality of life and End of life Decision-making. The stoic nature of donkeys can results in prolonged unacceptable suffering.

References

1) Thiemann, A. K., Buil, J.and Rickards, K.(2021). A review of laminitis in the donkey. Equine Veterinary Education. 34(10) 553-560. Available from: doi.org/10.1111/eve.13533

2) Van Dierendonck M.C., Burden, F.A. and Rickards, K. (2020). Monitoring acute pain in donkeys with the Equine Utrecht University Scale for Donkeys Composite Pain (EQUUS-DONKEY-COMPASS) and the Equine Utrecht University Scale for Donkey Facial Assessment of Pain (EQUUS-DONKEY-FAP) Animals.10(2) 354. Available from: doi.org/10.3390/ani10020354

3) The Donkey Sanctuary (2020a) Donkey Body Condition Score chart. Available from: https://www.thedonkeysanctuary.org.uk/research/sites/uk/files/2020-01/body-scoring-chart-revised-01-2020.pdf.

4) The Donkey Sanctuary (2020b) Donkey weight nomogram. Available from: https://www.thedonkeysanctuary.org.uk/research/sites/uk/files/2020-01/donkey-weight-estimator-chart-revised-january-2020.pdf

5) Burden, F. A., Du Toit, N., and Hazell-Smith, E. (2011). Hyperlipaemia in a population of aged donkeys: description, prevalence, and potential risk factors. Journal of Veterinary Internal Medicine. 25(6)1420-5.

6) Barrio, E., De Blas Giral, I., Thiemann, A. K. and Vasquez Bringas, F. J. (2020) Demography, preventative health care and reasons for relinquishment of donkeys to an equine charity. Equine Veterinary Journal. 53(2) 324-330. Available from: doi.org/10.1111/evj.13310

7) Burden, F. A. and Bell, N. (2019) Nutrition and Malnutrition of donkeys. Veterinary Clinics of North America Equine Practice 35(3) 469-479.

8) The Donkey Sanctuary (2020c). Environment Enrichment: The Donkey Sanctuary’s Guide to Enriching the Lives of Donkeys and Mules. Available at: https://view.pagetiger.com/EnvironmentalEnrichmentforDonkeys/EnvironmentEnrichmentfordonkeys [Accessed September 19 2020].