Gastrointestinal diseases in rabbits are being recognised with increasing frequency. A pet rabbit presented with anorexia, weight loss, changes in defecation and depression can present a diagnostic and therapeutic challenge for the clinician. Diet- and stress-related problems predominate, and preventive treatment plays a large role in managing these conditions. However, gastric ulceration and bacterial, viral, parasitic, idiopathic and neoplastic diseases are also seen frequently in pet rabbits. This article provides an overview of the common gastric conditions seen in rabbits, including their diagnosis and the options for treatment. The common causes, diagnosis and approach to the management of intestinal diseases will be discussed in an article to be published in the March issue of In Practice.
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Brigitte Lord graduated from the Royal Veterinary College in 2002. After a period in exotic and small animal practice, she spent time at the Royal (Dick) School of Veterinary Studies in Edinburgh and the University of Bristol/Bristol Zoo, and ran a rabbit and exotics veterinary referral service in south-west England. She returned to Edinburgh in 2008 as a lecturer in rabbit medicine and surgery, and is now head of the university's exotic animal handling facility. She is also the veterinary adviser for the British Rabbit Council. She holds the RCVS certificate in zoological medicine and is currently working towards the diploma in zoological medicine.
History and physical examination
When presented with a rabbit with gastrointestinal disease, it is important to obtain a complete history, as this may indicate the duration and severity of the disease. Young rabbits are more likely to develop bacterial or parasitic disease and, unlike other species, are also more likely to be affected by neoplasia. The feeding history is often of value, as it may draw attention to dietary indiscretions or an inappropriate diet being fed.
The owner should be asked about:
■ The duration of anorexia, decreased defecation or diarrhoea, as appropriate;
■ The appearance of the rabbit's faeces;
■ Whether there are uneaten caecotrophs in the rabbit's housing;
■ Whether signs of abdominal discomfort (eg, pressing the abdomen to the floor, flinching or bruxism) are apparent;
■ Whether the rabbit has lost weight.
Rabbits do not vomit, as they have a well- developed cardiac sphincter and lack a vomit centre in the brain.
It is also important to perform a complete physical examination. Abdominal palpation is particularly useful in rabbits and may reveal abnormalities such as dough-like contents of the stomach and/or caecum, a gas- or fluid-filled stomach or bowel loops, or the presence of a neoplasm, intussusception or ascites. Auscultation of the abdomen should be carried out to assess the gut sounds. These are intermittent and their absence should not be over-interpreted.
The possibility of an extra-gastrointestinal disease should also be considered; for example, a thorough oral examination, under sedation if required, should be carried out to rule out dental disease as a primary or complicating factor.
A presumptive diagnosis may be possible based on the history and clinical signs. However, rabbits presenting acutely depressed or with chronic gastrointestinal disease will need a complete diagnostic work-up.
Gross faecal inspection
If the rabbit is producing faeces, a sample should be assessed for size, shape and consistency. Normal hard droppings are typically 5 to 10 mm in diameter, although this may vary with the size of the animal. They have a regular spherical shape, are easily crumbled and contain visible undigested fibre (Fig 1). In contrast, abnormal hard droppings are smaller, irregularly shaped and firm (Fig 2).
A normal caecotroph is a mucus-coated cluster of soft spheres (similar in appearance to a bunch of grapes); however, the shape may be distorted if the rabbit has sat or stood on it (Fig 3). Caecotrophs are normally ingested by the rabbit directly from the anus, so they should be seen only occasionally. Abnormal caecotrophs may be liquid and diarrhoea-like, or large and voluminous, similar in appearance to cat faeces.
Faecal examination for parasites
Examination of direct smears of fresh faeces, or of faeces suspended in 0·9 per cent sodium chloride, may reveal the eggs of the nematode Passalurus ambiguus, which are intermittently shed. Adult worms may also be identified in fresh faecal smears. Normal caecal protozoa may also be seen. Flotation techniques may be necessary to identify coccidia and Cryptosporidium species oocysts. Examination of these preparations at a magnification of x1000 will be required to identify Cryptosporidium parvum as it is the smallest of the coccidians. The use of immunofluorescence and acid-fast stains will improve the sensitivity of faecal examination as a diagnostic test.
Faecal bacterial culture
Bacterial pathogens of rabbits that may be cultured from the faeces include Salmonella species, Pseudomonas aeruginosa, Lawsonia intracellularis and Yersinia pseudotuberculosis.
Faecal occult blood test
A faecal occult blood test can be useful in indicating the possibility of a disorder that causes haemorrhage, such as gastrointestinal ulceration.
Haematology, serum biochemistry and urinalysis
Haematology may yield valuable additional information. Suitable sites for blood sampling include the lateral metatarsal vein (Fig 4), marginal ear vein, jugular vein and cephalic vein. Normocytic and normochromic anaemia are sometimes associated with chronic disease or malnutrition. Microcytic hypochromic anaemia may be found in rabbits with iron deficiency due to chronic blood loss such as that associated with gastrointestinal ulceration. Generalised leucocytosis or lymphocytosis is suggestive of lymphoma and leukaemia.
Serum biochemistry and urinalysis can help to rule out metabolic disorders such as renal failure and liver disease.
Plain and contrast abdominal radiography
Plain abdominal radiographs may reveal signs compatible with ileus, obstructive bowel disease or ascites. The use of upper gastrointestinal barium and/or a barium enema can demonstrate neoplasia and severe infiltrative disease.
Ultrasonography can be useful in assessing gastrointestinal tract motility and the thickness of the gastric and intestinal walls, and in identifying the presence of neoplasms. However, the large amount of gas that is often present in the gastrointestinal tract of an abnormal rabbit can limit the usefulness of ultrasonography.
Endoscopy and laparoscopy
Endoscopy of the distal colon can be very rewarding. However, the stomach normally contains food and fur, which can limit endoscopy of the stomach. The tight pyloric sphincter of rabbits prevents endoscopy of the small intestines.
Laparoscopy is also a useful technique in rabbits, and can be used to inspect the whole bowel. As it is a minimally invasive technique, it is associated with less postoperative pain and a shorter recovery period than more invasive procedures such as laparotomy. Rabbits have a thin abdominal muscle wall, so it is important to use threaded instrument ports that are secured with a purse-string suture to maintain a seal and prevent port slippage (Fig 5).
Samples of the mid- to distal small intestines, liver, pancreas and mesenteric lymph nodes can be obtained during endoscopy or laparoscopy. Laparotomy allows similar biopsies to be taken but, as described above, is a more invasive procedure. In addition, the formation of postoperative adhesions may increase the risk of chronic ileus developing.
Response to treatment
A rabbit's response to treatment may be useful in helping to establish certain tentative diagnoses. For example, a positive response to feeding a high-fibre diet consisting only of hay, water and a high-fibre recovery diet (eg, Critical Care; Oxbow) may help to confirm a diagnosis of gastric stasis or ileus, while a combination of fluid therapy, supportive nutrition and treatment with gastroprotectants might be used in suspected cases of gastric ulceration (see below).
Diseases of the stomach
Gastric stasis and ileus
Gastric stasis is primarily an acquired disorder caused by decreased motility of the stomach. Generalised ileus is a common continuation of this condition, which may arise as a result of mechanical obstruction or defective propulsion. Mechanical obstruction (eg, due to the presence of dehydrated, impacted ingesta secondary to chronic dehydration, foreign bodies or infiltrative lesions) will cause delayed emptying of the stomach. Defective propulsion is seen in cases with defects in the nerves or smooth muscles of the gastrointestinal tract.
Primary factors include:
■ Feeding a high-carbohydrate/low-fibre diet;
■ Post-surgical adhesions;
■ Lack of exercise;
■ Toxin ingestion (most commonly lead).
Secondary factors include:
■ Environmental or emotional stress. For example:
The presence of predator species or a dominant rabbit;
Changes in routine;
Extremes in temperature or humidity.
Anorexia and chronic dehydration can be both causal factors and consequences of gastric stasis and ileus. Systemic dehydration will lead to the gut contents becoming dehydrated and the impaction of normal stomach contents, which include loose hair lattices or trichobezoars.
The history and clinical findings of a firm, dough-like stomach on palpation allow a presumptive diagnosis of gastric stasis and ileus, and are suggestive of non-obstructive disease (see Table 1). In advanced cases, it may not be possible to differentiate between obstructive and non-obstructive stasis and ileus. Plain radiography in early cases will reveal a mass of hair and food with a similar appearance to normal ingesta. As the impaction in the stomach and, occasionally, caecum develops, a gas halo is often seen around the compacted material (Fig 6). A definitive diagnosis can be made only on exploratory laparoscopy or laparotomy, but these are high-risk procedures in these patients, which are likely to be already metabolically unstable.
Treatment and prognosis
In rabbits with non-obstructive ileus, aggressive medical management is required to prevent further deterioration and death. Patients with obstructive ileus will require surgery (see section on obstruction below). Hepatic lipidosis is a common complication and cause of death in rabbits with prolonged gastric stasis and ileus. Rehydration of both the patient and its stomach contents, using both oral and intravenous fluids, may be required, depending on the severity of the stasis or ileus.
The use of analgesics, such as partial or full opioids in the first instance and, once the patient has been rehydrated, non-steroidal anti-inflammatory drugs (NSAIDs), is also appropriate (see Table 2).
Prokinetics should be used to stimulate gastrointestinal motility. Ranitidine, which has prokinetic effects equal to those of cisapride (another prokinetic agent) as well as antacid actions, is, in the author's opinion, very useful in the treatment of gastric stasis and ileus (Redfern and others 1991). Metoclopramide is another option, but it is not as potent a prokinetic as ranitidine, and its actions are limited to the proximal gastrointestinal tract. Another prokinetic, domperidone, has been found to be very effective at stimulating contractions in the large intestines of rabbits, and can be a good alternative in cases that respond poorly to ranitidine or metoclopramide (Li and others 2009).
Nutritional support can be provided by syringe feeding a commercially available high-fibre recovery diet (eg, Critical Care; Oxbow) or pureed leafy vegetables and grass, four to five times a day. This helps to reverse the negative energy balance that will develop in rabbits with gastric stasis and stimulate motility. A wide variety of fresh vegetation should be offered daily to encourage the rabbit to eat.
In some cases, for example, a rabbit that resists being syringe fed, feeding via a nasogastric tube may be required. Nasogastric tubes can be easily placed in a conscious calm or weak rabbit, in a similar manner to that used in cats. It is advisable to radiograph the patient after placing the tube to check that it is in the correct position. Some rabbits will tolerate the tube without the need to be fitted with an Elizabethan collar; this will also enable eating and caecotrophy, and is less stressful for the animal (Fig 7). Blended and strained food can be fed via the tube. Flushing the tube with 5 ml of water before and after each feed will help to keep the tube patent. Nasogastric tubes can be left in place for several days. Prophylactic antibiotic treatment is recommended for these patients to help prevent rhinitis, which may develop if the nasal tissue was traumatised during tube placement.
Rehydration of patients with gastric stasis or ileus is likely to be more beneficial than treatment with liquid paraffin, papain enzyme, pineapple juice or bromelain, which may cause dysbiosis. Due to the tight cardiac sphincter of rabbits, it is debatable how effective treatment with simeticone or dimeticone would be in dispersing gastric gas.
Ingested objects such as matted hair, carpet, plastic or rubber can pass down a rabbit's oesophagus and become a gastric or intestinal foreign body. The pylorus is a common site of obstruction, and material or objects lodged in this area can obstruct gastric outflow.
Rabbits with gastric obstruction may be asymptomatic or show anorexia initially until acute abdominal pain and hypovolaemic shock rapidly develop (within 24 to 48 hours). Death often occurs within 24 to 48 hours after acute abdomen develops. Liver lobe torsion is the main differential diagnosis of acute abdomen in rabbits (Wenger and others 2009).
In patients with a gastric obstruction, the clinical signs are usually indicative of the problem. Obstructions can rarely be detected on abdominal palpation alone, which in itself has a high risk of causing trauma to the distended stomach and the liver, which may be friable secondary to hepatic lipidosis. Plain and contrast radiographs can be difficult to interpret because ingesta are normally always present in the stomach and caecum of rabbits. In addition, if barium contrast agent is used, it may be recirculated if coprophagy/caecotrophy occurs. In most cases, an exploratory laparotomy is required to confirm the diagnosis.
Treatment and prognosis
Gastric obstruction is a life-threatening condition that requires aggressive treatment. It is essential to stabilise the rabbit before performing a gastrotomy to maximise the chances of a successful outcome. Analgesia, intravenous or intraosseous crystalloid fluids at shock rates and systemic broad-spectrum antibiotics should be administered. Prokinetics are contraindicated in patients with an obstructive condition before surgery, but are useful postoperatively to stimulate gastrointestinal motility. Gastric decompression via a nasogastric or orogastric tube should always be attempted.
Where possible, the patient's serum electrolyte concentrations and acid-base status should be evaluated, as acidosis and/or ketosis may be present. Systolic arterial blood pressure should be measured using the same technique as that employed for cats; the reference range for systolic blood pressure in rabbits is 92·7 to 135 mmHg (Reusch 2005). Fluid therapy has been used to correct hypovolaemia in rabbits following the same principles as those used in cats and dogs.
Rabbits have an unnecessary reputation for being difficult to anaesthetise. However, paying careful attention to all aspects of the patient's perioperative care, addressing stress and treating underlying disease will optimise the safety and success of anaesthesia (see Box 1).
Box 1: Anaesthesia of rabbits for gastric surgery
The principles of good anaesthesia are to:
■ Provide excellent perioperative care;
■ Select agents suitable for the individual patient;
■ Ensure that the airway can be maintained and intermittent positive pressure ventilation can be given in an emergency;
■ Ensure that intravenous access is available to enable intraoperative fluid therapy and emergency drug administration;
■ Increase fluid therapy to 10 ml/kg/hour during anaesthesia.
Premedication and induction
It is vital to select a suitable anaesthetic regimen for a critically ill rabbit. The use of a2-adrenoceptor agonists is contraindicated in these patients. Premedication with 0·2 to 0·3 ml/kg fentanyl/fluanisone administered intramuscularly, followed by induction with 0·2 mg/kg midazolam given intravenously to effect 10 minutes later, will provide a smooth induction and good muscle relaxation, facilitating endotracheal intubation.
The rabbit should be preoxygenated before being intubated with a 2 to 3·5 mm endotracheal tube using the blind or visual technique (Longley 2008). Applying a lidocaine spray (eg, Intubeaze; Dechra Veterinary Products) to the glottis before attempting intubation may reduce laryngeal spasm.
Anaesthesia should be maintained using an inhalational agent such as isoflurane or sevoflurane. The use of local anaesthetic agents (eg, lidocaine or bupivacaine; see below) will reduce the dose of general anaesthetics required, thus reducing the side effects of these agents.
Local anaesthetic agents are very useful for providing local analgesia and can also provide good postoperative analgesia. Bupivacaine (1 mg/kg) and lidocaine (1 mg/kg), when used in combination, provide rapid-onset local anaesthesia and analgesia of long duration. The maximum doses that should be used in rabbits are 2 mg/kg bupivacaine and 10 mg/kg lidocaine. These agents can be injected into the midline skin and abdominal muscle at the site of the incision. The rabbit can be given a top-up dose of 2 mg/kg morphine, administered intravenously or intramuscularly, if additional analgesia is required during longer surgical procedures; this can be repeated during surgery if required.
Reversal of anaesthesia
At the end of the procedure, the fentanyl/fluanisone can be reversed by giving 0·5 mg/kg butorphanol, and the midazolam can be reversed with 0·05 mg/kg sarmazenil, both administered intravenously. A dose of 0·05 mg/kg buprenorphine should be given two hours after reversal, as butorphanol has a short half-life in rabbits, but is more effective than buprenorphine at antagonising the fentanyl/fluanisone.
Rabbits can be challenging surgical patients, but the chance of a successful outcome can be maximised by ensuring:
■ A good knowledge of the regional anatomy;
■ Adequate preparation of the patient;
■ The availability of suitable instrumentation;
■ That steps are taken to minimise the pain, fear and stress experienced by the animal.
The basic principles of surgery in rabbits are the same as those described for other domestic species. However, the surgical techniques and considerations may need to be modified to account for the unique anatomy, physiology and behaviour of this species. Box 2 outlines the procedure for performing a gastrotomy in rabbits.
Box 2: Step-by-step guide to gastrotomy in rabbits
■ Step 1. Make a standard midline incision. As the abdominal muscles and linea alba are very thin, care must be taken to avoid lacerating the abdominal organs on entering the peritoneal cavity
■ Step 2. Explore the abdomen fully
■ Step 3. Partially exteriorise the stomach. The abdomen should be packed adequately to prevent contamination
■ Step 4. Place stay sutures at the proposed incision site. The incision should be made in a non-vascular site along the greater curvature or between the greater and lesser curvatures of the stomach
■ Step 5. Inspect the stomach contents, and visually identify and remove any foreign material causing an obstruction
■ Step 6. Close the stomach with one layer of sutures placed in a simple continuous pattern followed by another layer in an inverting pattern. Only absorbable synthetic monofilament suture material (eg, polydioxanone [PDS II; Ethicon]) should be used for surgery in rabbits, as this species is very prone to forming adhesions
■ Step 7. Close the linea alba using a continuous or interrupted suture pattern
■ Step 8. Finally, close the skin with a simple continuous subcuticular pattern
The use of NSAIDs postoperatively has been shown to minimise the development of postsurgical adhesions. The rabbit should continue to receive supportive treatment for ileus, as described above. The prognosis is guarded to poor, as most rabbits with gastric obstruction have severe hepatic lipidosis, acidosis and ketosis. They are also likely to have severe gastric ulceration, which can progress to perforation with subsequent peritonitis. If perforation occurs, the prognosis is grave. Aggressive and early treatment will improve the chances of the animal recovering.
Gastric ulceration is a relatively common finding on postmortem examination of rabbits. In patients with gastric ulceration, other clinically significant disease (eg, anorexia, enteritis, typhlitis, intussusception, gastric impaction and bronchopneumonia) or periparturient death are common. The prevalence of the condition increases with age and it is seen more commonly in female rabbits than males. Stress – for example, as a consequence of another disease – has been suggested as an aetiology for gastric ulceration. Perforation and subsequent peritonitis have been found in 70 per cent of rabbits with pyloric ulceration (Hinton 1980).
Anorexia and signs of pain, such as bruxism and reluctance to move, can be the principal signs of gastric ulceration. Melaena is rare in rabbits. In some cases, clinical signs due to anaemia and hypoproteinaemia may be seen (eg, pale mucous membranes, dyspnoea, weakness, collapse and shock). Some ulcers may perforate and then seal rapidly by forming adhesions, leading to the development of abscesses within the gastric wall (Fig 8).
Signs of acute abdomen and sepsis may be observed in rabbits with perforation and peritonitis, and there may be evidence of peritonitis on plain radiography. Ultrasonography can be useful in detecting thickening of the gastric wall, which may be associated with chronic ulceration or abscessation. Endoscopy is the most sensitive and specific tool for diagnosing gastric ulceration in other species but, in rabbits, visualisation of the gastric wall will be very limited due to the ingesta normally present in the stomach.
Treatment and prognosis
The treatment of gastric ulceration will depend on the severity of the condition and whether the underlying cause has been detected. As discussed earlier, rabbits with gastric perforation and peritonitis have a grave prognosis. Symptomatic or prophylactic treatment could be considered in higher-risk cases such as female rabbits in late gestation, or patients with anorexia, enteritis or chronic disease. This involves decreasing the production of stomach acid, protecting the ulcerated mucosa, and providing fluid therapy, analgesia, broad-spectrum antibiosis and supportive nutrition.
Primary tumours such as adenocarcinoma and leiomyosarcoma of the stomach have been reported in rabbits. Lymphoma is the most common tumour of male rabbits and the second most common in female rabbits, after uterine adenocarcinoma, and has been found to infiltrate the stomach. Metastatic haemangiosarcoma has also been seen in the stomach. There is a wide age range in reported cases, although juvenile and young adult rabbits appear to be predominantly affected. Clinical signs shown by rabbits with gastric tumours can include anorexia, depression, cutaneous nodules (in cases of lymphoma), pallor, emaciation and peripheral lymphadenopathy. Some rabbits may show no signs until the disease is advanced and sudden death occurs. The duration of illness may range from one week to 10 months.
Iron deficiency anaemia and lymphocytosis, including immature and atypical lymphocytes, have been described in cases of lymphoma in rabbits. Bone marrow biopsies may be required in suspicious cases that have lymphocytosis without circulating atypical lymphocytes. Plain and contrast imaging may reveal gastric wall thickening. Ultrasound-guided fine needle aspiration of thickened lesions in the gastric wall may produce cytological preparations that are diagnostic. However, an exploratory laparoscopy or laparotomy to examine the stomach and take biopsies for histological evaluation are usually required for a definitive diagnosis.
Treatment and prognosis
Most cases of adenocarcinoma are likely to be too advanced for surgical resection, and these patients have a grave prognosis.
Various chemotherapy and radiation therapy protocols described for the treatment of lymphoma in cats or dogs could be extrapolated to rabbits, especially as most chemotherapy drugs have been studied and used in experimental rabbits. The prognosis would depend on the stage of the disease when diagnosed and its response to treatment.
Rapid diagnosis and appropriate treatment of gastric diseases will increase the likelihood of a favourable outcome in affected rabbits. A second article, to be published in the March issue of In Practice, will discuss the common causes, presentation, diagnosis and treatment of intestinal diseases in this common companion species.
Self-assessment test: Gastric diseases in rabbits
What are the four most important factors in the supportive treatment of rabbits with non-obstructive ileus?
What is the shock fluid rate for a rabbit?
What are the two main differential diagnoses for acute abdomen in rabbits?
What is the treatment regimen for a rabbit with suspected gastric ulceration?
What is the second most common tumour in rabbits?
Analgesia, nutritional support, fluid therapy and the administration of prokinetics
Obstructive ileus and liver lobe torsion
Decrease acid production, protect ulcerated mucosa, provide fluid therapy, analgesia, broad-spectrum antibiosis and supportive nutrition
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