The Gastrointestinal System
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In: The Clinical Companion of the Donkey (2nd Edition) by Evans L. et al.
Updated:
JAN 30, 2022
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INTRODUCTION
Most conditions of the gastrointestinal system present as in horses and ponies.
However, it is important to note that donkeys may be more sick than they appear, because their behaviour traits and physiology commonly result in a reduced expression of the severity of pain and dehydration when compared with horses and ponies.
The prevalence of colic varies according to the donkey population and can be a significant cause of mortality. The use of some key preventative health measures will reduce the incidence of colic and early identification will improve mortality rates. It is important to recognise subtle behavioural changes and a thorough examination and diagnostic evaluation is essential for the effective treatment of donkeys with colic. Surgical treatment of colic will not be discussed in this chapter, as the approach is the same as for the horse and pony.
There is a high risk of hyperlipaemia and gastric ulceration secondary to periods of inappetance or starvation and specific treatment of these conditions will ensure that the donkey has an improved chance of recovery.
Liver disease is relatively common in the UK population of donkeys, yet clinical signs may not be seen until advanced or end stage disease is present.
This chapter will cover the following subjects:
Key points
- Detecting colic can be difficult and/or delayed in donkeys due to their stoic nature and the subtle clinical signs displayed.
- Secondary hyperlipaemia is always a risk with colic/inappetence.
- A rectal examination is strongly advised when this can be safely undertaken.
- Obesity can complicate taking a peritoneal tap, obtaining a good ultrasound image, and surgical access to the abdomen.
- There is a strong association between dental disease and colic.
PREVENTION
- Good preventative management practices will reduce the incidence of colic, particularly regular dental care, appropriate diet, and strategic parasite control.
The gastrointestinal system of the donkey is similar in anatomy to that of horses and ponies, but there are a few important differences.
- Narrow nasal meati necessitate use of a narrow bore pony or foal sized tube for nasogastric intubation.
- The stomach of a 150-200kg donkey seems to tolerate a maximum bolus of 3 litres approximately delivered by stomach tube.
- The length of the small intestine is relatively longer, around 6 m per 100 kg (vs 5 m for the horse), the transverse colon is short (10 cm), and the small colon is approximately 1 m.
The donkey is a desert adapted animal, and appears to retain fluid in the hindgut and caecum and tolerate dehydration better than the horse. It is likely that a combination of physiology and stoic behavioural traits mean that donkeys do not present with clinical signs of dehydration until at a more advanced stage, so it is worth bearing in mind that they could be dehydrated, even when presenting few clinical signs. Monitoring urine output will be useful if blood markers of dehydration are not available.
Donkeys with colitis do not tend to present with profuse diarrhoea as horses often do.
The risk factors for the occurrence of colic in the donkey depend on the population under investigation.
Working donkeys globally are more likely to be fed inappropriate or dry feed, have access to rubbish and an inadequate water supply. There are also likely to be an absence of effective programmes for parasite control and a limited availability of drugs, all of which will increase the risk of colic.
A working donkey – scavenging on inappropriate feed from rubbish dumped in the area.
Companion donkeys may not receive good preventative treatments such as regular dental examinations and effective parasite control strategies. This will increase the risk of colic, as will inappropriate changes in diet
and management.
In the UK, studies have shown that the most common type of colic encountered in the donkey is impaction colic of the pelvic flexure and caecum.
The common risk factors for impaction colic include:
- increasing age
- dental disease
- access to concentrate feed
- reduced water intake.
CLINICAL EXAMINATION
See Appendix 1 for a summary of the clinical examination.
A thorough clinical examination of the donkey must always include a period of observation of their behaviour. Because recognition of the subtle signs of illness in the donkey are often delayed, the animal may be more compromised than expected or than initial appearances suggest. It is important to watch how the donkey responds to being offered food, and whether they eat and drink effectively.
Taking a thorough history will help to identify any risk factors which would predispose to colic. Any changes in feed or management, as well as practices such as worming or frequency of dental examinations should be noted.
⚠ ALERT
Anorexia or a reduction in appetite may result in hyperlipaemia. This can complicate the clinical picture and make diagnosis of colic challenging.
Donkeys can be challenging patients to treat when they present with colic because the nature of the donkey’s pain-related behaviours will often mask clinical signs and the subtle changes in behaviour rarely give an indication of the urgency of the condition. Inappetence or anorexia as a result of a condition in the gastrointestinal system in donkeys will quickly induce hyperlipaemia. This complicates the donkey’s behavioural and physiological responses and makes diagnosis and treatment more difficult, especially if surgery were to be considered.
See Chapter 7: Hyperlipaemia and the Endocrine System for more information.
Remember that the physiological parameters of the donkey differ from those of horses and ponies.
Information
Adult donkey physiological parameters
- Temperature: 36.5—37.8oC
- Pulse: 36—52 beats/minute
- Respiration: normally 20 breaths/minute
but with a range of 12—28 breaths/minute
A pulse rate of over 70 would indicate severe disease, hypovolaemic shock or pain.
Donkeys are reported to have an increased ability to tolerate dehydration; capillary refill time and pulse quality may remain more normal than expected in the face of fluid loss.
Clinical and behavioural signs
The behaviour of donkeys in response to pain is different to that of horses and ponies, with the donkey often showing more subtle behavioural indicators of pain in response to equivalent pain stimuli.
See Chapter 1: Behaviour for more information.
Typical colic signs in the donkey include:
- dullness
- isolation from companion or group
- behaviour change
- reduced appetite/ sham eating
- a selective appetite, which may favour grass but reject hard food and forage
- lying down or recumbent.
Donkeys will often lie in sternal recumbency and are quieter and more calm than a horse with colic, who would tend to lie flat out in lateral recumbency.
Further indicators of pain include a lack of ear movement and lowered head carriage.
A dull donkey showing typical signs of colic: depression, low head posture and immobile ears.
The plastic rubbish recovered from the donkey pictured to above.
Signs of acute abdominal crisis are usually less evident than in the horse. They include flank watching, weight shifting, kicking at the abdomen and lying down and rolling. In severe cases, terminally ill or exhausted donkeys may be unresponsive.
The signs of colic in the donkey are often vague and non-specific, and therefore a thorough clinical examination is essential whenever a dull donkey is presented.
Issues may arise with the small size of the donkey, making clinicians wary of performing basic clinical procedures such as rectal examination and nasogastric intubation. Obesity can impede effective ultrasonography and peritoneal taps. There is little space in the lumbar fossa for ultrasound examination of deeper structures, and fat deposits can complicate imaging.
DIAGNOSTIC PROCEDURES
A dental examination using a Hausmann gag (oral speculum) should be carried out because there is a strong association between dental disease and colic. It may not be appropriate to treat any underlying dental disorder until the colic is resolved.
Stomach tubing should be carried out using either a pony or foal stomach tube to check for reflux. The prominent large nasopharyngeal recess may make the procedure more difficult.
Adequate lubrication and restraint will help reduce the risk of haemorrhage. If administering oral fluids it is important to remember the comparatively smaller size of the stomach to avoid over filling.
A rectal examination should be performed if safe to do so. Most donkeys tolerate the procedure well but some may require restraint and/or sedation. Good lubrication will aid the procedure and spasmolytic medication such as butylscopolamine can be used where appropriate to facilitate the examination.
While the clinician may be unable to palpate the abdomen extensively, useful information such as faecal consistency and mucosal hydration can be determined, even from a limited rectal examination.
An abdominal ultrasound examination may assist in identifying abdominal lesions in small donkeys, although subcutaneous fat may obscure detail. Careful preparation of the patient prior to ultrasound, including clipping and washing of the area to be scanned will facilitate the examination and help improve image quality.
A peritoneal tap can be difficult to obtain due to thick adipose deposits along the ventral body wall. This procedure may require use of a catheter, spinal needle or teat cannula in combination with ultrasonic guidance if available. The needle/trocar needs to be long enough to pass through the ventral abdominal fat, which can be up to 14cm in thickness; a 19 gauge 2 inch needle can be used.
A faecal sample can be used to assess endoparasite burdens and fibre length of forage. Dry faecal consistency or an excess of mucus may reflect prolonged transit time and developing hyperlipaemia.
⚠ ALERT
Consider hyperlipaemia in all cases of colic, either as a primary factor leading to ileus or as a secondary complication due to the reduction in appetite.
A blood sample to check haematology and biochemistry parameters. Note that donkey specific parameters must be used.
See Appendix 4 for the normal haematology and biochemistry reference ranges.
A serum sample to check for triglyceride levels is advisable because hyperlipaemia can be a complicating factor in all cases of colic, either as a primary factor leading to ileus, or as a secondary complication due to inappetence. If there is any doubt about the donkey’s nutritional intake, it is preferable to provide energy enterally or parenterally whilst waiting for laboratory results.
A donkey should not undergo surgery for colic until the triglyceride status has been evaluated.
See Chapter 7: Hyperlipaemia and the Endocrine System for more information.
COMMON CONDITIONS
Conditions related to upper GI tract: stomach and small intestine
Gastric ulceration is more common than in the horse and pony because the donkey is more susceptible and the risk is increased during periods of inappetence, hyperlipaemia and when fed concentrate feeds intermittently.
Donkeys are unlikely to present the same clinical signs of gastric ulceration as a horse or pony, but diagnosis and treatment options are similar to those for the horse and pony, with the caveat that prolonged fasting to ensure gastric emptying prior to gastroscopy can put donkeys at further risk of hyperlipaemia. Gastrointestinal transit time is longer in donkeys compared with horses and ponies. Currently, starving for longer than 12 hours is not recommended. The procedure should be abandoned if there is insufficient gastric emptying after a 12 hour fast. It should be noted that insufficient gastric emptying is highly likely in donkeys after just 12 hours.
Data from post-mortems carried out at The Donkey Sanctuary have identified that most chronic inactive ulcers are located in the squamous area adjacent to the margo plicatus. Acute ulcers are more rarely identified but have been found in both the squamous and glandular areas of the stomach.
Gastric impaction or delayed gastric emptying are seen secondary to liver disease or generalised ileus, or as a primary condition in certain populations of donkeys with access to poor quality, dry feedstuffs or foreign bodies such as plastic bags.
Small intestinal lesions are uncommon but can be diagnosed and managed as in the horse and pony. Despite the fact that many donkeys are overweight, strangulating lipomas appear to be a rare cause of colic in the donkey.
Small intestinal malabsorption can be tested for as in the horse and pony, using the oral glucose absorption test (OGAT) but careful consideration of the risks of prolonged fasting should be made. Because donkeys tend to have slow gastric emptying, the value of the test is questionable as it is likely that food material will remain in the stomach after a 12 hour fast and may affect glucose absorption and transport.
Equine grass sickness is rarely reported in donkeys, but should be kept as a differential diagnosis of weight loss, inappetence and ileus in the United Kingdom.
Parascaris impactions have been found in donkeys carrying heavy burdens of this parasite.
Conditions related to lower GI tract: caecum to rectum
Impaction of the pelvic flexure and caecum are very commonly identified problems. The mortality rate of donkeys with impaction colic has been shown to be higher than that of horses and ponies. This may be due to a number of factors including delay in presentation of disease, concurrent hyperlipaemia and concurrent medical problems.
Most donkeys with impaction colic present with only low grade signs of discomfort and a significant number will have a degree of hyperlipaemia. When treating these animals, enteral feeding by stomach tube (foal or pony sized is advised) along with the use of laxatives is recommended.
An appropriate solution would be three litres of warm water with electrolytes, glucose, magnesium or sodium sulphate, and a high-fibre nutritional supplement such as a ground instant oat breakfast cereal. The laxative may only need to be given on one or two occasions (if given more than once then it is preferable to use sodium sulphate). The nutritional support element may need to be continued. Withholding forage is important whilst waiting for the impaction to clear, but complete starvation can exacerbate hyperlipaemia and ileus. Offering grass or soft mashes during treatment will help to prevent this.
⚠ ALERT
With all cases of colic, the donkey undergoing treatment needs to be kept in close proximity to its bonded companion, to prevent separation stress which may exacerbate anorexia and hyperlipaemia.
Large intestine displacements and volvulus can occur in donkeys. Some animals will show obvious signs of pain, in others it may be less evident and may present later in the course of disease.
Colitis does not often present with diarrhoea. It may present with weight loss, dullness, pyrexia, tachycardia and ventral oedema due to hypoalbuminaemia. In acute cases signs of abdominal pain such as rolling may be seen.
The causes are the same as in horses and ponies, but cyathostomes should always be considered, especially as donkeys often have irregular, or no, parasite control.
Infectious diseases, such as salmonella and clostridia, must also be ruled out and it is important to note that diarrhoea is not always present.
Stress can be a significant trigger for colitis in donkeys. Blood work is an essential part of a diagnostic work up, where available, and the presence of hypoalbuminaemia should raise suspicion. If there are concurrent changes in the leucogram and several animals are affected then an infectious cause should be considered and appropriate diagnostics performed as for other equines and appropriate biosecurity measures put in place.
Typhlocolitis is a serious medical emergency in the donkey, with generally poor outcomes despite intensive treatments.
If a primary cause can be found, then specific treatment can be initiated – for example, treatment of larval cyathostominosis. Otherwise treatment will be as for the horse and pony, with the complication of hyperlipaemia included as a poor prognostic factor.
A multifocal to coalescing, severe, ulcerative and fibrinonecrotic typhlocolitis.
⚠ ALERT
It can be difficult to monitor food intake and faecal output in donkeys because of the need to house with bonded companions
Liver Disease is a significant cause of mortality and morbidity in the UK donkey population.
Clinical signs are often absent until disease is severe but can include weight loss, fever and depression. Liver disease is often subclinical and often detected based on serum biochemistry evaluation. Where blood biochemistry is indicative of liver disease further investigation may be warranted, particularly if there are clinical signs of weight loss and intermittent low grade abdominal pain. Liver dysfunction from excessive fat infiltration from a negative energy balance, stress or insulin insensitivity may occur with severe hyperlipemia.
Diagnosis of liver disease is similar to horses and ponies and ultrasonography and biopsy can provide useful information. There is no validated hepatic histopathology scoring system for donkeys; liver disease is graded using the horse system. Treatment of donkeys showing mild to moderate raises in liver enzymes with no clinical signs may follow an initial plan of changing forage if dusty or mouldy, feeding a balancer supplement and repeating bloodwork in 4-6 weeks to monitor trends in liver enzymes.
Rectal Prolapse
Rectal prolapse is seen more commonly in working donkeys, where exhaustion and parasitism are common. Treatment is the same as for horses and ponies.
Colic unrelated to GI tract
As the signs of colic may be subtle, the list of differential diagnoses for a donkey with non-specific dullness is extensive.
Abdominal neoplasia is a significant cause of low-grade, recurrent colic episodes in geriatric donkeys. Abdominal neoplasia involving either the gastrointestinal tract, liver, kidney or female reproductive system was found in 9.5% of geriatric donkeys examined post-mortem at The Donkey Sanctuary.
Typical cases can be hard to diagnose, especially if the donkey is on pain relief medication.
Colic signs have been displayed by donkeys with pyometra, enlarged ovaries and urolithiasis, underlining the importance of a rectal examination in all cases of colic.
Ovarian pathology associated with low grade colic. This is an ovarian haematoma, most likely a haemorrhagic anovulatory follicle. There was also associated serosanguineous peritoneal effusion.
PREVENTION
⚠ ALERT
Good preventative health care has been proven to reduce the incidence of colic.
The preventative health measures listed below have been proven to reduce the incidence of colic:
- providing regular dental checks and appropriate treatment
- feeding fibre appropriate for dental health – for example, short chop for geriatric donkeys
- supplying bedding materials appropriate for dental health (because donkeys will eat bedding)
- implementing all changes in diet and management gradually over a two week period
- providing constant trickle feed fibre and adequate exercise
- applying strategic parasite control
- providing constant access to fresh water.
Mules & Hinnies
Mules appear to show an increased repertoire of pain behaviours and therefore may show more obvious signs of colic.
Mules may also be less susceptible to hyperlipaemia as a secondary complication of colic.
Further information
Factsheets, research and detailed information can be found online at: thedonkeysanctuary.org.uk/for-professionals
The Working Equid Veterinary Manual: thebrooke.org/for-professionals/ working-equid-veterinary-manual
Cox, R., Burden, F., Proudman, C., Trawford, A.F. and Pinchbeck, G.L. (2010) Demographics, management and health of donkeys in the UK. Veterinary Record 166(18), pp 552—556.
du Toit N., Burden F. and Dixon, P.M. (2009b) Clinical dental examinations of 357 donkeys in the UK. Part 2: Epidemiological studies on the potential relationships between different dental disorders, and between dental disease and systemic disorders. Equine Veterinary Journal 41(4), pp 395—400.
Burden, F.A., Gallagher, J., Thiemann, A.K. and Trawford, A.F. (2009) Necropsy survey of gastric ulcers in a population of aged donkeys: prevalence, lesion description and risk factors. Animal 3(2), pp 287—293.
Cox, R., Burden, F., Gosden, L., Proudman, C., Trawford, A. and Pinchbeck, G. (2009) Case control study to investigate risk factors for impaction colic in donkeys in the UK. Preventative veterinary medicine 92(3) pp 179—187.
McGorum, B.C. and Pirie, R.S. (2010) Asinine typhlocolitis; ‘scouring’ the literature for diagnostic and aetiological clues. Equine Veterinary Education 22(2), pp 58—59.
Morrow, L.D., Smith, K.C., Piercy, R.J., du Toit, N., Burden, F.A., Olmos, G., Gregory, N.G. and Verheyen, K.L.P. (2010) Retrospective analysis of post– mortem findings in 1,444 aged donkeys. Journal of Comparative Pathology 144(2-3), pp 145—156.
Thiemann, A.K., Rickards, K., Getachew, A.M. and Paraschou, G. (2017) Colic in the donkey. In: Blikslager, A.T., White, N.A., Moore, J.N. and Mair, T.S. (eds.) The Equine Acute Abdomen. Third edition. Wiley-Blackwell, New York, USA. pp 469—487.
Thiemann, A.K. and Sullivan, R.J.E. (2019) Gastrointestinal disorders of donkeys and mules. Veterinary Clinics of North America: Equine Practice 35(3), pp 419—432.
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How to reference this publication (Harvard system)?
(2018) “The Gastrointestinal System”, The Clinical Companion of the Donkey (2nd Edition). Available at: https://www.ivis.org/library/clinical-companion-of-donkey-2nd-edition/gastrointestinal-system (Accessed: 17 September 2024).
Affiliation of the authors at the time of publication
Sidmouth, Devon, EX10 0NU, UK.
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