Dealing with GI problems (Proceedings)

Gastrointestinal problems are by far one of the most common problems that initiate a visit to the vet for the pet rabbit. These problems include anorexia, diarrhoea, caecal dysbiosis, gastrointestinal stasis, bloat and obstruction.

When a rabbit presents for any condition involving the GI tract, a thorough history can provide invaluable clues as to the problem at hand. One of the best examples of this is a history of anorexia. It is imperative to sort out from the history whether the rabbit is not eating because it has no interest in food at all versus having a great interest in food, but just not wanting to take food into its mouth. A complete lack of appetite is most commonly seen secondary to a severe physiological problem such as renal failure, whereas a scenario involving a rabbit showing a keen interest in food but not eating it is a classic presentation seen in rabbits with dental disease. It is very important for the clinician to emphasize to him/herself that the GI tract starts with the mouth. The most common dental disease responsible for anorexia in rabbits is misalignment of the molars and resultant overgrowth of the crowns of the teeth. Dysfunction of the upper arcades of cheek teeth most often involves spurs that grow into the buccal surface of the mouth, and dysfunction of the lower arcades of cheek teeth most often involve spurs impinging on the lingual surface. Although these statements are true over 90% of the time, there are cases that involve lingual spurs on the upper arcade of cheek teeth and buccal spurs on the lower arcade of cheek teeth.

A cursory exam on the awake patient with an otoscope will often reveal the offending molar spurs. However, sometimes a more thorough exam of the mouth while the patient is sedated is necessary. If dental disease is the reason for the anorexia, it is best addressed by sedating the rabbit and filing down the molar spurs as needed. This is most efficiently accomplished with a small hand rasp or careful use of a dental bur. Bone ronguers can be used to clip off prominent spurs. This instrument is appropriate because it is designed to cut sharply as opposed to cutting by compression. Any instrument that would not cut the teeth sharply or file the spurs down appropriately could potentially cause longitudinal microfractures in the teeth that would provide a pathway for bacteria to seed the jaw and create a jaw abscess. When proceeding with dental work on a rabbit in any manner, care should be taken to maintain or reproduce a normal occlusal angle when addressing molar malocclusion (Crossley, 1996).

Other dental disease that can preclude a rabbit from eating properly is malocclusion of the incisors. Rabbits are hypsodonts and thus, their teeth grow continuously. Since the only way to wear any substance down is to cut it or abrade it with another substance that is as hard or harder than it, it is essential that no matter what the rabbit chews on, it's teeth are properly occluded. It is only by normal mastication of the teeth while they are properly lined up that they wear one another down appropriately. The best way to address incisor malocclusion is to completely extract all of the incisors. If the owner will not concede to this procedure, it will be necessary to trim the incisors every 4-6 weeks. This is best done with a dremmel tool or dental bur. The owner should be strongly discouraged from trimming them with nail clippers, as they are likely to cause longitudinal fractures in the teeth.

Whenever dental disease of any form is present, it is imperative to take radiographs of the skull to fully evaluate the extent of the disease process. Ventrodorsal, as well as right and left oblique views are useful for evaluation of the dentition.

Signs that should incite the clinician to further investigate the teeth as the source of the problem, other than overt molar spurs seen on initial exam, are mucopurulent discharge around the base of any of the teeth, excessive salivation and horizontal bars across the incisor teeth. Mucopurulent discharge is usually secondary to a tooth root abscess. Excess salivation is seen when there is irritation of the tongue by a molar spur that may not be visible on initial exam. Horizontal bars across the incisors are commonly seen in rabbits that have dental disease secondary to a calcium or vitamin D deficiency (Harcourt-Brown, 1996).

True diarrhoea is most often seen in young rabbits and is usually secondary to parasitism. The most common parasites to cause diarrhoea is Eimeria species of coccidia. In managing this disease in rabbits it is important to consider environmental factors such as crowding and damp, dirty conditions that contribute to the spread of coccidosis. For the oocysts to become infective, they need to be exposed to oxygen for several days (Harcourt-Brown, 2002). Fastidious cleaning as well as medical management with trimethoprim/sulfamethoxazole at a dose of 30-40mg/kg PO q 12 hrs and supportive care are necessary to treat rabbits for this condition.

Owners will frequently report a history of diarrhoea to the clinician that is not truly diarrhoea, but rather caecal dysbiosis. By carefully questioning the owner as to whether or not there are normal, dry faecal pellets passed on the same day as the supposed diarrhoea, as well as the nature and odour of the "diarrhoea" can help the clinician distinguish between true diarrhoea and caecal dysbiosis. In a case of caecal dysbiosis, rabbits do tend to continue passing normal dry faecal pellets on the same day that they pass loose excrement. The end product that is passed as a result of caecal dysbiosis is usually thick, pasty and has a very pungent odour.

Caecal dysbiosis occurs when the rabbit consumes a diet that is too rich in sugars and simple carbohydrates. Owners frequently feed a ration that has whole or cracked corn as well as dried fruits and seeds in it. Excessive amounts of fruit, crackers, cereals, and commercial "yoghurt drop" treats are often fed. If one stops to think about the way the caecum functions, it quickly becomes obvious why this creates a problem. In the rabbit colon, large particles are propelled out and are excreted in the form of dry, fibrous "waste" droppings. Small particles are moved retrograde back up to the caecum where they are processed by a well-balanced population of bacteria and yeast. The dominant bacterial population is Bacteroides species (Cheeke, 1987). The dominant yeast is Saccharomyces guttulatus. The main end product of fermentation by the Bacteriodes organisms is the volatile fatty acid, butyric acid. A considerable amount of energy is needed by these hindgut tissues because the rabbit colon is extensively responsible for absorption of electrolytes and nutrients. Butyric acid is the preferred fuel for this hindgut metabolism (Cheeke, 1987). Hence, Bacteriodes plays a significant role in the health and function of these tissues.

In cases of caecal dysbiosis, a large amount of Saccharomyces guttulatus is frequently seen on microscopic examination of the malformed caecotropes. A hypothesis of excessive sugars and simple carbohydrates causing this yeast overgrowth and an imbalance of the bacterial flora can be understood if one considers how yeast react in general. Consider that when making bread or beer it is essential to add sugar to the yeast mixture initially to "activate" the yeast. Adding excessive sugars to the "fermentation vat" of the caecum can quickly cause an overgrowth of yeast. Yeast overgrowth and caecal dysbiosis in general are best addressed with supportive care as indicated by the patient's status, and strict diet changes. All forms of sugars and simple carbohydrates must be eliminated from the diet and the rabbit needs to be encouraged to consume adequate amounts of coarse fibre. It is best to eliminate concentrated nutrition sources such as pellets at this time and put the rabbit on a diet strictly limited to hay and leafy green vegetables.

Although true trichobezoars can occur in rabbits, they do not occur as commonly as one would think. Most often a decrease in, or lack of production of faecal pellets is due to ileus or "gastrointestinal stasis" rather than a true hairball. Due to the nature of their grooming habits, rabbits always have some hair present in their GI tract. If they are taking in adequate amounts of coarse fibre and water this hair is passed regularly in the faecal pellets.

Typical physical exam findings in rabbits suffering from ileus include depression, hypothermia, a very doughy stomach and caecum, and gas filled intestinal loops. Radiographic findings include severely gas distended intestinal loops and a very small caecum. It is not uncommon to see a gas shadow around the gastric contents. This is especially true if the rabbit was anaesthetized with gas for the radiographs. When a rabbits become dehydrated, they pull water from their GI tract to keep the rest of their body hydrated. The result is very dry, compacted, doughy gastric and caecal contents. The gas shadow around the gastric contents is most likely due to aerophagia at the time of anaesthetic induction and the dehydrated gastric contents sticking together.

Ileus is an extremely painful condition. If one considers how painful it is for an adult human to have a small amount of intestinal gas and compare that to the degree of gas dilatation of the loops of intestine in a small rabbit with ileus, one would be inclined to provide liberal amounts of analgesics to a patient suffering from ileus. Useful analgesics for this condition are flunixin meglumine at 1-2mg/kg SC q 12-24hrs (Carpenter, 2001), meloxicam at 0.1-0.2mg/kg (Harcourt-Brown, 2002), or buprenorphine at 0.01-0.05mg/kg SC, IP, IV q 6-12 hrs (Carpenter, 2001).

Massive supportive care is often necessary to nurse a rabbit patient through a bout of ileus. Appropriate fluids such as lactated ringers or normal saline at 100mL/kg/day given subcutaneously as well as the syringing feeding of oral fluids will help restore normal hydration. Syringe feeding a commercial gruel such as Oxbow Critical Care or a pureed pellet and vegetable mix in small amounts, every few hours is necessary to avoid hepatic lipidosis. The patient should be provided with ad lib amounts of hay and leafy greens. Pharmacological agents used in the treatment of ileus include intestinal motility modifying drugs such as metoclopromide at 0.5mg/kg PO, SC q 4-12 hrs. (Carpenter, 2001) and cisapride at 0.5mg/kg PO q8-12 hrs. (Carpenter, 2001). Simethicone, in the form of infant anti-gas drops are useful to help break up the gas so that it will pass. One mL of a commercial infant anti-gas preparation such as Mylicon® PO q 4-8 hrs is helpful. Another adjunct agent to use is cholestyramine (Questran®). This product acts as an ion exchange resin to adsorb enterotoxins that can potentially damage the liver. One-eighth teaspoon of Questran® is added to 10mL of water and administered orally q24hrs. In case the cholestyramine should have an affinity for any medications as well, it is best to be cautious and administer the product several hours after other medications are given instead of at the same time. In addition to fluid, nutritional and pharmacological support, gentle abdominal massage is helpful to stimulate intestinal motility.

Rabbits presenting with a grossly distended, hard stomach usually have an obstruction of the distal duodenum. Rabbits have a very tight oesophageal sphincter and cannot vomit or eructate. They produce large amounts of saliva and gastric secretions. If there is an obstruction of the gastric outflow tract, the stomach quickly becomes distended. This condition can become life threatening very quickly. An excessive amount of pressure is put on the diaphragm, which compromises the rabbit's already small chest volume. In addition to the pressure that the engorged stomach puts on the diaphragm, the distention of the stomach itself perpetuates the problem by compressing the acute angle of the pyloric outflow tract. If the patient is stable enough to be anaesthesized, a gastric tube can be passed to relieve the pressure immediately. These cases are often obstructed because of a small mass of dehydrated ingesta. It is not uncommon for them to respond to decompression, fluid therapy and prudent use of metoclopromide. Appropriate pain management should be provided and if the situation is not resolving within 2-6 hours, surgical intervention is necessary. These patients need to be observed very closely until the condition is resolved.

The most common places for rabbits to have an obstruction in their GI tract are the distal duodenum and the ileocolic junction. Survey radiographs are useful for making the diagnosis and with timely surgical intervention rabbits usually recover from enterotomies quite well. Rabbits normally have a very slow GI transit time and thus oral administration of barium for contrast studies is often not useful. Since ileus is so common in rabbits, the main objective when evaluating abdominal radiographs is to distinguish between a case of intestinal obstruction versus ileus. In the case of ileus the gas pattern tends to extend all the way to the colon.

Rectal polyps are a condition seen fairly commonly on this distal aspect of the rabbit GI tract. These are usually benign papilomas that are removed surgical if they seem to be causing a problem such as bleeding or irritation. They are often pedunculated and removed easily by placing a cerclage ligature around the base of the mass and excising it completely.

By understanding the normal anatomy and function of the rabbit's GI tract from mouth to rectum, the veterinary practitioner can readily deal with the most common problems that rabbits are presented for due to this organ system's dysfunction.

References:

Carpenter J.W., Mashima T.Y., Rupiper D.J. Eds. Exotic Animal Formulary (second edition). Philadelphia: W.B. Saunders, 2001; p 304.

Cheeke, P.R., Rabbit Feeding and Nutrition. Academic Press. Orlando. 1987. pp25 and 84-85.

Crossley, D.A., Vet. Rec. 1996.

Harcourt-Brown, F. Textbook of Rabbit Medicine. Oxford: Butterworth Heinemann, 2002