Gastrointestinal Diseases of Pet RabbitsLisa Harrenstien, DVM

Gastrointestinal disease is the most common reasonthat pet rabbits are presented for veterinary evaluationand treatment. Most of the problems affecting a houserabbit's gastrointestinal health are caused by hereditaryor husbandry factors, many of which can be managedwith basic veterinary procedures and appropriate diet.Copyright© 1999 by W. B. Saunders Company,

Key words: Rabbit, lagomorph, nutrition, dentistry, gas-troenterology, gastrointestinal.

Signs consistent with gastrointestinal (GI) dis-ease in pet rabbits can include lethargy,

anorexia, hypersalivation or drooling, subman-dibular masses, diarrhea, constipation, tenes-mus, bruxism, ileus, abdominal masses, disten-tion or pain during palpation, and fecal soiling.Differential diagnoses for GI signs should in-clude inappropriate diet (usually too low in fiberor too high in carbohydrates), dental malocclu-sion, dehydration, and parasitism,· as well asnon-GI conditions such as neoplasia (eg, thy-moma, uterine adenocarcinoma), urinary tractcalculi, and trauma (especially musculoskeletalor neurological).

Anatomy and PhysiologyRabbits have open-rooted (continuously grow-

ing) incisors, premolars, and molars, with thedental formula of 2(1:1-2/1, C:O/O, P:3/2,M:2-3/3) = 26-28, Some pet rabbits do not havea second pair of upper incisors, or "peg teeth."The premolars and molars are far more neces-sary than the incisors for normal side-to-sidegrinding and mastication of fibrous food. Adiastema exists between the incisors and "cheekteeth" (premolars and molars). The intermaxil-lary space is greater than the intermandibularspace, as in horses; therefore, premolar andmolar malocclusion often involves lateral (buc-cal) overgrowth of the maxillary teeth and me-dial (lingual) overgrowth of the mandibularteeth. In the awake rabbit, the angle of openingofthe oral cavity is quite small.

Rabbits have a simple stomach with a .well-developed cardiac sphincter that anatomically

precludes the ability to vomit. 1 Masses of foodand hair are normally present in a rabbit'sstomach, but with normal GI function, thesemasses are eventually passed along the GI tractfor excretion. The stomach is never empty in anormal rabbit; gastric emptying time may be aslong as 3 days. Gastric pH is normally 1 to 2 inthe mature rabbit, which kills most microorgan-isms; suckling rabbits' gastric pH is 5 to 6.5, how-ever," which allows the hindgut to develop its nor-mal bacterial population, but also makes youngrabbits vulnerable to bacterial enterocolitis.

The small intestine of rabbits has similaranatomy and physiology to other familiar spe-cies. The pylorus, proximal duodenum, andileocecocolic area are potential sites ofGI obstruc-tion. A gall bladder is present on the right mediallobe of the liver. The hindgut (cecum and colon)has important roles in digestive physiology, in-cluding selective separation and rapid excretionof fiber, fermentation of remaining nutrients inthe cecum, and production of cecotropes (alsocalled "cecal pellets" or "night feces"), whichare later consumed by the rabbit for conserva-tion of beneficial microbes and vitamins Band K.Cecotropes are covered with mucus, which pro-tects them from gastric acid for at least 6 hours,therefore allowing fermentation and lactic acidproduction within the cecotropes to continue."

NutritionAlfalfa-based pellets typically available in pet

stores were originally designed to be fed toproduction rabbits (those raised for meat or furpurposes), therefore their protein content ishigher and fiber content is lowerthan would beideal for pet rabbits. Higher-than-ideal proteinlevels will cause a decrease, then an increase incecal pH, allowing pathogenic bacteria to prolif-

From Oregon Zoo, Portland, ORAddress reprint requests to Lisa Harrenstien, DVM, c/o Veteri-

nary Hospital, Oregon Zoo, 4001 SW Canyon Rd, Portland, OR97221.

Copyright © 1999 by W.B. Saunders Company.1055- 937X/99/0802-0006$1 0, 00/0

Seminars in Avian and Exotic Pet Medicine, Vol 8, No 2 (April), 1999: pp 83-89 83

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Table 1. Useful Tools for Gastrointestinal Evaluationand Treaunent in Rabbits

Lisa Harrenstien

erate there. Lower-than-ideal levels of indigest-ible fiber will cause cecal hypomotility and predis-pose the rabbit to enteritis and diarrhea.v" Anabsolute minimum of 10% dietary crude fiberhas been recommended in production rabbitfeeds. Because of differences in fiber use bydifferent rabbit breeds, it is impossible to specifyfiber requirements for pet rabbits, but the factremains that adequate fiber is extremely impor-tant for rabbit GI health, and it is probably safeto recommend that rabbit owners choose dietscontaining the highest fiber available. Most petrabbits do best when fed a grass hay-based diet.f

Gastrointestinal ConditionsDental Malocclusion

A thorough discussion of history and a carefulphysical examination are important for evalua-tion of oral disease. Animals with painful teeth,jaws, or oral mucosa will be reluctant to eat, ormight not be able to smell, prehend, chew, orswallow food well. Owners may notice that theirrabbit is steadily losing weight, although foodgets scattered around its cage. Body fur mightappear unkempt, if a painful rabbit is no longerusing its mouth for grooming. Maxillary ormandibular abnormalities may be palpable orevident during initial visual examination, beforethey seem to affect the rabbit's behavior or appetite.Hypersalivation can have many causes, includingoral soft tissue disease; drooling might not be obvi-ous, but there may be other signs such as wet frontpaws. Halitosis can be a sign of intraoral infection.

During your physical examination, it is impor-tan t to palpate for asymmetry and/ or pain in therabbit's mandibles, maxillae, and overlying sub-cutaneous tissue. Lift the lips to examine incisorlength, occlusion, and color. Use an otoscopewith medium to large cone attached to examinethe premolars and molars; do this by holding therabbit's head stationary with one hand anddirecting the otoscope through the diastemainto the mouth for a lighted view of the oralcavity (Table 1). Most rabbits object to theotoscope procedure (and their lips and tongueoften obstruct your view); therefore, be pre-pared to work quickly. The intraoral examina-tion of a rabbit should include evaluation ofpremolar/molar positioning and length, anyprotruding "points" (usually on the rostral as-pect of premolars, buccal surfaces of the maxil-

Otoscope with large cone (for examining cheekteeth), or nasal speculum with integrated lightsource

Lempert (small-tip)rongeursSmall thin raspsWire cutters with fine sharp tipsDremel moto-tool with circular cutting tip, protective

eyewearand maskDental handpieceTongue depressors (break in half to make them nar-

rower)Long cotton-tip applicatorsPouch retractors, cheek dilators, human eyelid

retractor, or vaginal speculumHigh detail radiographic equipment, ideallywith mag-

nification abilityComplete blood cell count (CBC) and chemistry

panel collection suppliesFecal parasite examination suppliesCytologicalexamination suppliesMicroscopeSwabsfor sample collection for aerobic, anaerobic,

and fungal culture/sensitivity testingReference laboratory familiar with rabbit blood han-

dling, cultures, parasite examinations, and cytologyFood blenderVarietyof food items including formulated diets, hay,

vegetables, baby food, liquid diets, activecultureyogurt, source of healthy rabbit feces or cecotropes

Red rubber feeding tubes 8 French (Fr) and smallerElizabethan collars (cat-sizeand smaller)Intravenous catheters (20-gaugeand smaller)Spinal needles for intraosseous catheterization (20-

and 22-gauge)Transparent chamber for anesthetic inductionHeating pad, stockinette, towel,or bubble wrap to

counteract hypothermiaIsoflurane anesthesia machineSmall-diameter endotracheal tubes, sizes2.0 mm to 3.0

mm, uncuffedLaryngoscope with narrow bladeLong 3.5-Frpolypropylene cathetersUp-to-date exotic animal formulary and stocked phar-

macySmallvolume syringes «1 mL) and needles 25 gauge

(ga) or smaller

lary teeth, or lingual surfaces of the mandibularteeth), exudate or bleeding, and any lacerationsor ulcers or white plaques on the adjacentmucosa. If the rabbit is anesthetized for theexamination, a blunt probe can also be used toevaluate each tooth for looseness.

Malocclusion is the most common dentalabnormality seen in pet rabbits. Incisor malocclu-sion usually presents as prognathism, in whichthe mandibular incisors grow rostral to the

Gastrointestinal Diseases of Pet Rabbits 85

maxillary incisors; this results in overgrowth ofall incisors. Normally, the mandibular incisors ofrabbits should be worn down by occlusion withthe "peg teeth" caudal to the first set of maxillaryincisors. Inheritance of prognathism likelyaccountsfor its high incidence rate in rabbits." Other causesfor malocclusion include jaw trauma or apical jawabscesses.Malocclusion and overgrowth can also beseen in premolar and molar teeth; this is not alwayscoincident with incisor malocclusion, but can resultfrom incisor malocclusion.

Treatment of malocclusion traditionally in-volves periodic trimming of affected teeth every1 to 2 months, because rabbits' incisors grow upto 1 ern per month. There are varying opinionsabout which tool(s) should be used for incisortrimming; available options include wire cutters,dog nail trimmers (Resco; Teela Co, WalledLake, MI), low- or high-speed dental handpiece,or a rotary power tool (Dremel Multipro; Dre-mel Co, Palm Springs, CA) with a diamond diskor bur attached. It is often stated that teeth maysplit and shatter longitudinally when wire cuttersor nail trimmers are used to trim incisors, there-fore the power equipment methods are prefer-able, but some practitioners do not regard this asa major risk, especially if hand trimming equip-ment is sharp .. If incisors do shatter, apicalabscessation and/or maldirected incisor growthis likely in the future, and incisor extraction willbecome necessary."

Dental radiographs are recommended beforeextraction, especially if infection or involvementof other teeth or bone is suspected. An IS-gaugeneedle, #15 scalpel blade, or small-breed eleva-tor/root tip pick elevator is used to break downperiodontal ligaments, starting with the lowerincisors. The medial ligament of each tooth isthe most important one to loosen. Insert theelevator deeply to the level of the bony alveolus,rotate it, and hold that position for 10 seconds.Repeat this technique at the lateral, buccal, andlingual aspects of the same tooth, then grasp thetooth and pull gently and firmly in the direction(arc) of tooth growth. If the tooth is extractedcompletely, its base should appear as a hollowtube. Upper incisors are extracted in a similarmanner, but they are more curved. Hemostasis isusually not a major concern during incisor extrac-tion, and it is not necessary to pack tooth socketswith antibiotic or other material postextraction,although it is wise to flush the sockets with dilute

chlorhexidine solution postextraction for me-chanical removal of debris. Take the opportunityto culture the sockets for aerobic and anaerobicbacteria if you are concerned about tooth rootinfection, and consider whether at-home flush-ing of the sockets should be prescribed. Rabbitscan be offered their normal food (includinghay) postoperatively, but should also be offered awater-soaked version of their normal food. Post-operative analgesia (butorphanol 0.1 to 0.5mg/kg intravenously or subcutaneously every 4hours, or buprenorphine 0.01 to 0.05 mg/kgsubcutaneously, intramuscularly, or intravenouslyevery 6 to 12 hours, or flunixin meglumine 1.1mg/kg subcutaneously or intramuscularly every12 hours or fentanyl 12.5 pg by patch) is impor-tant to encourage early return to normal eatingbehavior. Be aware that the "peg teeth" are oftenbroken during extraction of the upper incisors.If the peg teeth or any other incisors are brokenduring surgery, they should be allowed to growagain for approximately 6 to S weeks and thenextracted.

Premolar and molar malocclusion can beprimary in origin, secondary to trauma, or sec-ondary to chronic incisor malocclusion andovergrowth (Fig 1). These teeth (or their"points") are trimmed in an anesthetized pa-tient using small rongeurs, a small file, or ideally,a high-speed dental handpiece. Because the oralcavity is so narrow, it is difficult to see affectedteeth clearly and protect adjacent soft tissuestructures; a focal light source and an assistant orspecialized retractors are necessary for this proce-dure (large size rabbit/rodent pouch dilator androdent incisor gag, available from Dr Shipp'SLaboratories, Beverly Hills, CA). Severely maloc-eluding cheek teeth may result in apical migra-tion of the maxillary tooth roots toward the orbitor deeper into the mandible, causing palpableexostoses on the mandible. If periodontal dis-ease and malocclusion are this severe, extractionof the offending cheek teeth is indicated. Extrac-tion of premolar or molar teeth should beaccomplished using an intraoral approach; naso-tracheal intubation with a 2.0-mm endotrachealtube will be necessary for this procedure. Bloodtransfusion may be indicated during extractionof cheek teeth, especially if there has beenchronic inflammation or extensive surgicaltrauma. Gingival closure should be attemptedafter cheek tooth extraction, using 4-0 or smaller

86 Lisa Harrenstien

absorbable suture, to decrease bacterial invasionof underlying soft tissues and bone.

Mandibular abscessation is fairly common inrabbits and carries a grave prognosis for cure.Radiographs will show expansile destruction,lysis, and sclerosis in the area of inflammation'Fiz 1). The bony changes usually result fromextension of an apical abscess (often caused bycheek tooth malocclusion) or subcutaneous ab-

. Treatment involves aggressive surgical de-ridement (including tooth extraction) and long-

a!TID antibiotic therapy, but recurrence ofessation is extremely common. Gelfoam satu-

Figure 1. Lateral skull ra-diographs of two anesthe-tizedadult rabbits. (A)Man-dibular osteopenia, toothloss, incisor malocclusion,premolar malocclusion,andmolar malocclusion ("wavemouth"). This radiographwasmade 2 years after man-dibular trauma occurred inthis rabbit. Mandibular ab-scessation in rabbits is oftenassociated with these radio-graphic findings. (B) Nor-mal dental and mandibularappearance. The left zygo-matic arch and left orbitshowradiographic evidenceof bony lysis and sclerosis,as an inflammatory re-sponse to an orbital mass.

rated with antibiotics such as ceftiofur, or methyl-methacrylate beads impregnated with antibioticssuch as amikacin, have been used to fill the areaafter curettage in an attempt to provide highantibiotic levels locally in surrounding tissue. Acontroversial but potentially more successful treat-ment option for mandibular abscesses includesuse of calcium hydroxide paste8,9; after debride-ment and cleaning of the abscess cavity, the cavityis filled with calcium hydroxide paste, which isbactericidal due to its pH of 12.0. The paste isremoved after 1 week and replaced if purulentmaterial is again seen.

Gastrointestinal Diseases of Pet Rabbits 87

Gastric Trichobezoars (Hairballs) /Deus

Historically, gastric trichobezoars have beendescribed as the most important and commonGI condition afflicting pet rabbits. This may betrue, but theories as to cause, and thereforetreatment, have changed substantially over thepast several years. Originally believed to becaused by overgrooming and subsequent pres-ence of large amounts of hair in the stomach,this condition is now believed to be secondary toabnormal GI physiology and motility, which itselfis secondary to dehydration or a diet of low fibercontent. As mentioned earlier, masses of hair aretypically present in a rabbit's stomach and areeliminated with normal peristaltic activity of theentire GI tract. If gastric pH is increased orperistalsis is decreased (ileus) as a result of GI orextra-GI illness, masses of hair and food willaccumulate in the stomach and can eventuallycause true pyloric or proximal duodenal obstruc-tion, with gastric tympany and mucosal (or moresevere) damage.

Treatment of this condition should be aimedat reestablishment of adequate hydration, GImotility, and gastric pH. Fluid therapy (lactatedRingers solution 150 mL/kg/day), metoclopra-mide (0.5 mg/kg given orally or subcutaneouslyevery 8 hours), cisapride (0.5 to 1.0 mg/kg givenorally once daily), mineral oil, cat laxatives, Bvitamins, and force-fed blenderized alfalfa pel-lets, fruits, and vegetables have been seen toimprove GI motility and overall health.lv-!' Place-ment of an intravenous catheter in the cephalic,lateral saphenous, or caudal auricular vein or anintraosseous catheter in the proximal femur ortibia permits hydration to be corrected. Subcuta-neous fluids can also be administered. Anorecticrabbits should be force-fed up to four times dailywith as much high-fiber food as they will willinglytake. A 5-French or 8-French nasogastric feedingtube can be placed in the rabbit in a mannersimilar to that used in the cat. Alternately, agastrostomy tube can be placed with endoscopeguidance, using a similar technique as in cats.FAn Elizabethan collar may be required to main-tain integrity of either type of indwelling tube.Equine enteral products (Nutriprime; KenVet,Ashland, OH) can be administered throughnasogastric tubes, or blenderized regular dietscan be administered through gastrostomy tubesfor higher fiber content.

Feeding fresh pineapple juice (approximately10 mL per day), which contains the enzymebromelain.l" papaya tablets that contain pa-pain.l" or proteolytic enzymes (eg, Viokase-V;Fort Dodge Laboratories, Fort Dodge, IA) hasreportedly aided the breakdown and passage oftrichobezoars, although the value of these prod-ucts is questionable. There is no evidence thatthese products can degrade hair. 14,J5 It is possiblethat they may aid in the breakdown of trichobe-zoars by dissolving the proteinaceous matrix thatbinds them together.

If the rabbit has gastric tympany that cannotbe medically relieved, or appears obstructed, orthe rabbit has been completely anorectic formore than 72 hours, surgical exploration andpotential gastrotomy should be considered. Ag-gressive supportive therapy before and aftersurgery is recommended to optimize the chancesof a successful outcome.

Bacterial Enteropathies

Diarrhea in pet rabbits is commonly caused bybacterial imbalances in the small and largeintestine and cecum. Constipation can also beseen with diarrheal disease, for example, inyoung rabbits because of formation of plugs ofmucous diarrhea ("mucoid enteritis'tj.J" Bacte-rial imbalances can result from diets too low infiber and too high in protein (therefore increas-ing cecal pH and encouraging dysbiosis), 17 anti-biotic usage, or weaning stress. Antibiotics re-ported to cause fatal diarrhea in rabbits includeclindamycin, lincomycin, erythromycin, amoxicil-lin (with or without clavulinic acid), ampicillin,cephalosporins, and oral penicillin.P'[' althoughit is important to realize that individual rabbitsmay also respond adversely to "safe" antibioticssuch as the quinolones and tetracyclines. A dietcontaining close to 20% fiber seems to maintainan optimum cecal pH to prevent changes in thenormal microbial flora. Treatment of dysbiosis islargely supportive and includes fluid therapy,nutritional support with high-fiber slurries, andbacterial support via transfaunation of freshcecotropes from a healthy rabbit. Some practitio-ners also administer pancreatic enzyme supple-ments. Metronidazole (20 mg/kg given orallyevery 12 hours) can also be given to combatclostridial overgrowth, but selective overgrowthmay still occur.

Although it is unclear how orally adminis-

88

nique used to diagnose canine oxyuriasis is notapplicable. Passalurus has a direct life cycle and isnonpathogenic in rabbits.i" However, if treat-ment is elected, this may include ivermectin (0.2to 0.4 mg/kg given subcutaneously), fenben-dazole (20 mg/kg given orally once daily for5 days), thiabendazole (50 mg/kg in two treat-ments 3 weeks apart) ,25 or piperazine (200 to 500mg/kg/ day given orally for 2 days) .23

Rabbits can also serve as intermediate hostsfor the canine tapeworm Taenia pisiformis. Trans-mission occurs through the contamination ofwater, feed, or bedding with canine feces. Clini-cal signs may include lethargy, abdominal disten-tion, and weight loss. Treatment is usually notrequired. However, rabbits passing proglottidsegments or ova in their stools can be treatedwith praziquantel (5 to 10 mg/kg given orally,subcutaneously, or intramuscularly once, andthen repeated in 10 to 14 days). Canine fecalcontamination should be avoided in rabbit areas.

Rabbits harbor a nonpathogenic intestinalyeast Saccharomycopsis gutulatus,26 which may bemistaken for coccidia or bacilli. This yeast doesnot require treatment.

Lisa Harrenstien

tered live bacterial cultures (in the form ofprobiotic supplements or active-culture yogurt)can survive rabbits' gastric pH, it is likely thatdiseased rabbits have higher gastric pH, andtherefore, more bacteria will survive to recolo-nize the cecum. Once a more benign bacterialpopulation exists in the cecum, perhaps thenBacteroides sp. and other normal cecal inhabit-ants can proliferate. One study stated that liveLactobacillus culture may prevent enterotoxemiaby decreasing the numbers of Escherichia coli inthe digestive tract.22 There is at least anecdotalevidence to suggest that active-culture yogurt is auseful adjunct to treatment of rabbit dysbiosis.

Gastrointestinal Parasitism

Coccidial infections, which can also causediarrhea, are the most common intestinal para-sitic problem in rabbits. Intestinal coccidiosis,caused by Eimeria species, can be diagnosed byfinding oocysts in a fecal sample. Intestinalcoccidiosis is a greater risk to young rabbitsbecause of the accompanying acute dehydration,but can also cause severe illness in older rabbitsas a result of intestinal mucosal damage andresultant sepsis. Treatment includes aggressivefluid therapy to counteract the dehydration.Trimethoprim-sulfadiazine (30 mg/kg givenorally every 12 hours for 7 to 10 days) orsulfadimethoxine (50 mg/kg given orally onceand then 25 mg/kg given once daily for 3 weeks)may be used. Rabbits that survive infection gener-ally are immune to future infections.P

A hepatic form of coccidiosis caused by Eime-ria stiedae also occurs in rabbits. Clinical signsmay include anorexia, weight loss, hepato-megaly, and diarrhea. Antemortem diagnosisand treatment are similar to that for the intesti-nal form. With the hepatic form, however, ab-dominal enlargement and hepatomegaly may bepresent. Abdominal radiographs and ultrasonog-raphy may be used to confirm hepatomegaly.Because infective oocysts are passed in feces, therabbit's cage, food bowl, and water bottle shouldbe routinely disinfected.

Other intestinal parasites are less of a problemin rabbits than in many other domestic species.The most common helminth parasite seen in therabbit is the pinworm Passalurus ambiguus. Adiagnosis is made by finding pinworm ova in thefeces. Rabbit pinworms do not deposit eggsaround the anus, so the transparent tape tech-

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Gastrointestinal Diseases of Pet Rabbits 89

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