Nearly all the disease problems in rabbits are directly or indirectly related to diet. The two most common rabbit emergency problems, which result in anorexia, are gastric stasis and malocclusion involving the incisors, cheek teeth or both.

Gastric stasis is one of the most common syndromes in rabbits and is characterised by anorexia, decreased or no stool production, and a large stomach filled with dough-like stomach contents and hair. A high-carbohydrate, low-fibre diet causes disruption of gastrointestinal motility and frequently leads to gastric stasis. There is a loss of liquid from the material in the stomach and the resultant dehydrated mass of gastric ingesta may not be passed by the rabbit. The material in the stomach usually consists of ingested food ± hair.

Malocclusion of the incisors, cheek teeth, or both is common in rabbits. Incisor malocclusion is usually apparent to the owner, while malocclusion of the cheek teeth is rarely obvious to the owner. Rabbits usually present with a history of anorexia and weight loss.

Pathophysiology

Rabbits are herbivores and hindgut fermenters. Their digestive system is driven by the presence of fibre in the diet, which allows efficient digestion of the non-fibre portion of food. High-fibre diets stimulate caecocolic motility, and have a low level of carbohydrate and thus decrease the risk of enterotoxaemia caused by carbohydrate overload of the hindgut. Frequently, a reduction in the amount of fibre in the diet, an increase in carbohydrate consumption and disruption of gastroenteric motility lead to alterations in the caecal pH and disruption of the complex bacterial flora of the hindgut. The spore-forming anaerobes, consisting mostly of Clostridium spp., and coliform species, such as Escherichia coli, increase as the population of normal organisms decreases. This leads to enterotoxaemia, sepsis and death.

Hepatic lipidosis develops rapidly when a rabbit stops eating, and reversing this process can be difficult. The author uses the same principles as used in the cat for anorexia and gastric stasis. The aetiology of gastric stasis in the rabbit is often a low-fibre diet but is also commonly seen with stress (as occurs in the cat).

Pelleted diets, when fed exclusively, are high in calories (high in digestible carbohydrates), high in protein and highly digestible, and designed to increase weight in growing rabbits raised for meat. These diets, when fed exclusively or in large quantities, cause gastrointestinal complications such as gastric stasis, obesity and malocclusion (decreased grinding action that keeps the occlusal surface evenly worn).

Malocclusion of the incisors is frequently a genetic trait. Malocclusion of the premolars and molars is common in middle-aged to older animals and may result from many factors. It leads to overgrowth and sharpening of the lateral (upper arcade) and the medial (lower arcade) edges. Common causes of malocclusion are:

 Genetic factors leading to a mandible that is too narrow or too short, resulting in misalignment of the teeth

 Decreased chewing action of rabbits fed an all-pellet diet

 Trauma and infections can increase the risk of malocclusion problems

Clinical Findings

 Anorexia for more than 2 days' duration.

 Malocclusion identified on oral examination.

 Weight loss may be noted in some rabbits.

 Ptyalism and ocular discharge (upper cheek teeth are very close to the nasolacrimal duct) should make the clinician think of dental disease.

 When gastric stasis is present, a firm, dough-like mass is often palpated in the cranial region of the abdomen. Gas may be palpable in the stomach or intestines. The number of faecal pellets is significantly reduced or absent. The stools passed are much smaller than normal or may contain hair.

Differential Diagnosis

 Gastric or intestinal obstruction. This can be from a large mat of fur or, rarely, from ingested foreign material like carpeting or bedding. Rabbits present with an acute abdomen, that is painful, bloated and with a tympanic stomach. The rabbit is usually in shock. Decompression of the stomach is required by passage of a nasogastric tube. Radiographs may show a dilated, fluid-filled stomach or caecum. Animals must be treated for shock and then taken to surgery. The prognosis for surgery is poor.

 Enterotoxaemia from other causes, such as reproductive disorders, bacterial enteritis, or pneumonia.

 Parasites.

Diagnostic Tests

Radiology may or may not be helpful in diagnosis of gastric stasis because the mass of food and hair appears similar to normal ingesta. However, visualisation of a large, ingesta-filled stomach on a radiograph of a rabbit that has been anorexic suggests the presence of gastric stasis.

Complete blood count (CBC) and serum chemistries are performed to evaluate the rabbit for other causes of gastric stasis, such as infections, hepatic or renal disease. A minimum database (i.e., blood glucose, packed cell volume (PCV)/total protein (TP) and azostick, electrolyes and acid-base) should be performed immediately. This will alert the veterinarian to possible hypoglycaemia secondary to anorexia, dehydration, azotaemia, and anaemia.

Evaluation of the teeth is necessary. Incisors are relatively easy to evaluate. The lower incisors should oppose the peg teeth and the four main incisors should have a bevelled cutting edge. Cheek teeth are more difficult to evaluate without general anaesthesia. Initially an otoscope is used to evaluate the cheek teeth for the presence of points. Palpate the ventral line of the mandible. It should be smooth along the ventral aspect of the mandible. If any bumps are palpated they likely indicate cheek tooth root disease. Skull radiographs under general anaesthesia are required when dental disease is suspected. Four views are taken: dorsoventral (DV), lateral, right lateral oblique and left lateral oblique. Mask anaesthesia with isoflurane and subsequent intubation is recommended. The author commonly uses etomidate (2 mg/kg i.v.) with diazepam (0.5 mg/kg) intravenously. Gas anaesthesia is not required for short procedures. Teeth specula and cheek dilators developed by Dr David Crossley are helpful in getting a good look at rabbit cheek teeth crowns. In most cases the upper cheek teeth develop spurs on the lateral aspect while the lower teeth develop spurs medially. These can cut into the cheek gingiva or the tongue, causing anorexia and a lot of pain.

Treatment

1.  Stop all inappropriate antibiotics, such as ampicillin, amoxicillin or clindamycin. These antibiotics reduce normal gastrointestinal flora, allowing other flora to proliferate and leading to changes in intestinal pH, gastrointestinal dysbiosis and sometimes diarrhoea.

2.  Fluid therapy: perfusion and dehydration are corrected initially. Rabbits commonly present in hypovolaemic shock and are extremely dehydrated. It is very important to correct the hypovolaemia and dehydration prior to treatment for gastric stasis.

3.  Treat hypoglycaemia when <3.9 mmol/l by adding 50% dextrose to the fluids to produce a 2.5% dextrose solution. When the animal is symptomatic with seizures and hypoglycaemia, treat with a 1:1 solution of 50% dextrose with saline at 1 ml/kg i.v. The author has also seen hyperglycaemia in a stressed rabbit (up to 21.4 mmol/l) and in rabbits that were anorexic for more than 2-3 days. The author has observed that rabbits have a hyperglycaemic response to stress, similar to that seen in cats. Clinically the author has seen rabbits presenting with gastric stasis having a blood glucose between 8.3 to 20.0 mmol/l which corrects to normal with fluid therapy.

4.  Place a nasogastric tube for nutrition and rehydration of the stomach contents. The tube can be used for a primary gastric stasis, anorexia or after performing dental procedures. The technique is as follows:

a.  A 5-8 French Argyle® tube is chosen. The length necessary to reach the stomach is determined by measuring from the tip of the nose to the last rib. Do not use a stylet since the oesophagus of the rabbit can be perforated with any additional force. Local anaesthetic (2% lidocaine gel) is placed into the rabbit's nostril. The rabbit must be properly restrained, protecting its back, and the head ventrally flexed by an assistant. The tube is passed ventrally and medially into the ventral meatus. As long as the neck is ventrally flexed the tube will automatically enter the oesophagus (nasogastric tube will enter the trachea when the head is extended so that the trachea is perpendicular to the table surface). The end of the tube is advanced until it enters into the stomach.

b.  Verification of placement is determined with a radiograph and/or aspiration of gastric contents.

c.  Feeding procedure: A 35 ml syringe is used for slow bolus delivery of a liquid diet. The liquid diet used for the rabbit is the enteral nutrition. The diet contains some fibre, though not enough to meet the needs of a rabbit requiring long-term feeding (greater than 2-3 days). A 2 kg average adult rabbit requires approximately 175 Kcal/day. The feeding schedule using the enteral herbivore diet consists of mixing 20 ml/kg of water with 13 ml/kg of diet. The slurry is given into the nasogastric tube with a syringe every 6 hours. The tube should be flushed with 5-6 ml of tap water after each feeding. In the author's experience most rabbits will start to eat and produce stools after 1-2 days. Intravenous fluids are given for correction of perfusion and rehydration, after which nasogastric tube feedings with water and the fibre diet alone can supply nutritional requirements. The tube can remain in place until the rabbit can eat on its own and stool production begins.

d.  Gastrointestinal motility is induced with cisapride 0.5 mg/kg liquid suspension into the nasogastric tube every 8 hours.

Pain Relief

Pain or discomfort may require the use of analgesics such as butorphanol at 0.2-0.3 mg/kg i.v., i.m. or s.c. A constant rate infusion of butorphanol at 0.1 mg/kg/h has also been used by the author for pain relief in rabbits. The author has not seen any effects on gastrointestinal motility but no studies have been done. Injectable carprofen has become available in the USA, but it is unlikely to be labelled for use in rabbits. Carprofen is not a potent inhibitor of prostaglandin synthetase. Ketoprofen is available as an injectable agent but, because of its COX-1 inhibition, should be reserved for postoperative administration. Meloxicam has recently become available as an injectible and oral form, and is the most commonly used non-steroidal antiinflammatory drug (NSAID) in the rabbit. The dose of meloxicam is 0.2 mg/kg for the first dose and then followed with 0.1 mg/kg every 24 hours. It has primary COX-2 inhibition. NSAIDs should not be used in animals with pre-existing renal disease, hypovolaemia, bleeding disorders or if severe surgical haemorrhage is anticipated. Flunixin meglumine is a NSAID and is a very potent inhibitor of cyclooxygenase. Recommendations for its use in rabbits and ferrets with gastric stasis and septic shock are common in literature. This is most likely due to its use in horses with colic. The author warns against its use with pre-existing renal disease, hypovolaemia or bleeding disorders, as with any NSAIDs. Newer NSAIDs that are specifically COX-2 inhibitors may be safer than flunixin to use in ferrets and rabbits. The author does not use NSAIDs for initial treatment of pain associated with gastric stasis unless the rabbit is well hydrated, with no pre-existing renal disease, hypovolaemia or bleeding disorders. NSAIDs can be used after the rabbit is fluid-resuscitated and rehydrated.

Treatment with Force Feeding

Syringe feeding the critical care herbivore diet may be best for the mildly ill patient with adequate perfusion parameters and normal hydration, and where the rabbit has been anorexic for <24 hours. These animals may be sent home with instructions for care by the owner. The directions for quantities to feed are written on the can. The syringe tip fits into the diastema (the large space between the incisors and premolars). The rabbit can be wrapped in a towel if it is uncooperative. This may be very stressful to a rabbit and therefore is not recommended in the moderately to severely ill patient.

Treatment of Dental Malocclusion

Initial examination of the mouth is performed under general anaesthesia using a mouth gag. A slow-speed drill with a straight handpiece using a No. 8 HP burr is the instrument of choice to trim incisors and remove points form cheek teeth. Alternatively, some authors recommend the use of a rongeurs. If there is radiographic evidence of mild root disease (increased lucency at the tips of the roots) but there is no evidence of infection, burring the crowns to the gum line may be all that is required. If there is evidence of osteomyelitis (lysis and proliferation of bone surrounding a tooth), the tooth should be removed.

Anaesthesia used by the author for removal of points on the cheek teeth with a burr is as follows:

1.  Pre-emptive analgesia with butorphanol at 0.4-0.8 mg/kg s.c., i.m.

2.  Placement of an intravenous catheter and titration of anaesthesia using etomidate at 1-2 mg/kg with diazepam at 0.5 mg/kg i.v.

Broad-spectrum antibiotics are used after invasive dental procedures:

 Enrofloxacin 5-15 mg/kg orally q12-24h.

 Trimethoprim-sulphonamide (sulfamethoxazole + trimethoprim oral suspension) 15-30 mg/kg orally q12h.

Pain medications to be sent home are NSAIDs, such as meloxicam at 0.2 mg/kg i.v., s.c. or i.m. initial dose and then followed orally at 0.1 mg/kg q24h for 3-5 days as long as there is no evidence of pre-existing renal disease and the rabbit is perfused and well hydrated.