The Anorexic Rabbit: Part 2
Frances Harcourt-Brown, BVSc MRCVS
Harrogate, N. Yorkshire, UK
Clinical examination of the anorexic rabbit
A careful clinical history and a thorough physical examination are important in the differential diagnosis of the anorexic rabbit. Many cases require urgent treatment. The clinical signs of an abdominal catastrophe are a dramatic, sudden loss of appetite, abdominal pain and severe depression and many of these patients require prompt surgery. Urgent treatment is needed for obese rabbits, pregnant or lactating does that are at risk of rapidly developing hepatic lipidosis. Liquid diarrhoea in the absence of hard faeces is an emergency that can be rapidly fatal. True diarrhoea should be differentiated from uneaten caecotrophs, which is not a life-threatening condition. Caecotrophs consist of soft strongly-smelling faecal material and are often mistaken for diarrhoea by both owners and vets.
The clinical history may reveal physiological factors, such as loss of a bonded companion that can cause anorexia. Food intake is reduced during periods of water deprivation, perhaps due to an oversight by the owner, a faulty drinker or a frozen water bowl. Faecal output is an important part of the history. The absence of hard faeces signifies a disturbance in normal digestive function, such as gastrointestinal hypomotility or mucoid enteropathy. Small faecal pellets indicate insufficient indigestible fibre or reduced food intake. The passage of mucus, either on its own or mixed with soft faeces is a non-specific sign of disrupted digestive function.
Soiled or wet perineal fur indicates an underlying problem such as uneaten caecotrophs, urinary tract disease or perineal dermatitis. Inflamed, painful perineal skin can, in itself, cause stress and anorexia and any soiled fur must be examined closely for the presence of maggots.
Abdominal palpation should be done carefully and gently because the thin-walled viscera are easily traumatised. The liver and spleen are not palpable in the normal rabbit. Both kidneys can be identified as mobile structures. The stomach may be palpable as a hard round mass in rabbits with gastric stasis or as a distended structure in rabbits with gastric dilatation. The caecum may or may not be palpable in the ventral abdomen. The size and contents vary with diet and time of day. A full caecum is felt as a doughy mass. An impacted caecum is felt as a hard sausage-like structure. The bladder may or may not be palpable in the caudoventral abdomen. Rabbits with urinary tract problems often void urine in response to palpation of the bladder. The uterus is not palpable unless it is enlarged uterus due to pregnancy, neoplasia or pyometra. Abdominal masses may be neoplasms, impacted organs, abscesses, foetuses (normal, mummified or ectopic) or areas of fat necrosis. Fat necrosis can be a sequel to ovariohysterectomy or other abdominal surgery.
Dental disease is the most common cause of anorexia in pet rabbits. It is often manifested by ptyalism and a wet chin. Anaesthesia is required for a thorough examination of the oral cavity.
Radiography is a valuable diagnostic tool for anorexic rabbits. Underlying painful conditions such as spinal deformities, arthritic conditions, bone disease, abdominal neoplasms, urolithiasis and gastrointestinal abnormalities may be seen. Radiopaque deposits in the bladder are due to the presence of calcium carbonate. This can be a normal finding or may indicate the presence of 'sludgy' urine. Uroliths may be seen anywhere in the urinary tract including the kidneys. Nephrolithiasis can be associated with mineralisation of other soft tissues, especially the aorta.
Gastric dilatation can be seen clearly on abdominal radiographs. In rabbits, gastric dilation is usually due to intestinal obstruction and the site of the obstruction can be elicited from abdominal radiographs. The intestine proximal to the site of obstruction is distended by gas and fluid. In some cases, a moving foreign body is present and its progression can be monitored radiographically. Once it passes through the ileocolic junction, gas shadows are seen in the proximal colon. Gastric dilatation is also seen in the terminal stages of mucoid enteropathy. In these cases, the caecum is full of impacted material that can be seen radiographically and the colon is distended with gas and mucus.
Accumulation of gas in the caecum, stomach and proximal colon signify gastrointestinal hypomotility. Gas shadows surrounding impacted food or a 'hairball' in the stomach give it a characteristic halo.
Blood sampling anorexic rabbits
Artefactual errors are common in rabbit blood samples because their blood haemolyses easily and clots quickly. A guaranteed fasting sample is not possible because of caecotrophy. Stress can increase blood glucose and alter haematological parameters such as the distribution of neutrophils and lymphocytes. Anaesthesia affects some parameters, especially potassium. However, despite these limitations, blood sample results can be useful diagnostic or prognostic indicators for the anorexic rabbit.
Haematocrit values greater than 45% are indicate dehydration. Values of less than 30% indicate anaemia. Chronic renal failure or debilitating disease such as dental disorders or abscesses can cause anaemia. Uterine adenocarcinomas can be a site of intermittent blood loss. Total white cell counts are often not helpful. Rabbits seldom develop leucocytosis, even in response to active infection. Low white blood cell counts, especially lymphocyte counts, are found in association with chronic disease.
Hypoglycaemia is a significant finding in association with anorexia. A drop in blood glucose contributes to the development of ketoacidosis and fatty degeneration of the liver. Hyperglycaemia is often stress related. Handling alone can cause an increase in blood glucose. Acute, marked hyperglycaemia is associated with painful conditions such as acute intestinal obstruction. Blood glucose levels can rise as high as 20-25mmol/l and return to normal once the condition is resolved. Hyperglycaemia is seen in the terminal stages of gut stasis and, in conjunction with other signs, is a poor prognostic sign. It is associated with hepatic lipidosis, which can give a range of bizarre blood results.
Small fluctuations in serum urea concentrations are difficult to interpret. Pre-renal azotaemia commonly occurs during periods of dehydration. Urea and creatinine values that would signify renal disease in other species may be due to dehydration and can return to normal once the rabbit is rehydrated. Apart from dehydration, other factors such as dietary protein concentrations, withholding food and natural diurnal rhythms also influence blood urea concentrations.
Treatment of the anorexic rabbit
The anorexic rabbit requires prompt diagnosis and treatment. The underlying cause must be addressed and non-specific treatment is required to prevent gastrointestinal hypomotility and death from hepatic lipidosis.
Dental problems require treatment under general anaesthesia. Sharp spurs can be removed with dental burrs or handheld clippers. Either method requires a gag, cheek dilators, good illumination and competence at using the equipment. There is debate about the use of both power equipment and handheld instruments for rabbit dentistry. Both methods have advantages and disadvantages. The advantage of hand held equipment is that it is unlikely to cause serious soft tissue damage. The disadvantage is that it is not possible to shape the teeth precisely. Dental burrs do not shatter the teeth and give greater control over the final size and shape. However, there is a risk of serious iatrogenic damage.
Exploratory laparotomy and intestinal surgery is indicated for rabbits with intestinal obstruction or abdominal masses. Good anaesthesia, pre- and post- operative care are essential to prevent stress, dehydration, electrolyte and acid base imbalances and to stimulate gastrointestinal motility. Gradual mask induction of anaesthesia with isoflurane and endotracheal intubation are recommended. Premedication with fentanyl/fluanisone (Hypnorm, Janssen 0.2-0.3ml/kg, intramuscularly) provides analgesia, sedation and vasodilation that facilitate radiography and intravenous fluid therapy.
Inappropriate antibiotic therapy in rabbits can cause diarrhoea and death from enterotoxaemia. The choice of antibiotic and its route of administration are important. As a general rule, parenteral therapy is safer than oral medication. Clindamycin, lincomycin and ampicillin are high-risk antibiotics for causing enterotoxaemia. Penicillin and cephalosporins are safe if given by injection but are candidates for inducing diarrhoea if they are given orally. Enrofloxacin, trimethoprim/sulpha combinations and tetracyclines appear safe by any route.
Fluid therapy is indicated for many conditions. Intravenous administration into the marginal ear vein is simple, especially in sedated or moribund rabbits. Lactated Ringers or Hartmanns solution is suitable for most situations.
Non-specific treatment for the anorexic rabbit
Reduce stress. A warm, secure quiet environment. Gentle handling
Provide a bed of hay. Palatable hay tempts rabbits to eat, stimulates gut motility and provides a sense of security and familiarity.
Provide tempting foods such as freshly picked grass, dandelions, spring greens, cabbage, kale, carrots or apple. Soft fruit, lettuce and other salad items should be avoided.
Reduce pain by using analgesics. NSAIDs (e.g., carprofen 2-4mg/kg) and/or narcotic analgesics (e.g., buprenorphine 0.01-0.05mg/kg) can be used in rabbits.
Use motility stimulants, such as cisapride (0.5mg/kg) or metoclopramide (0.5mg/kg)
Syringe feed rabbits that have not eaten for more than 24 hours. Cereal based baby foods or small mammals recovery diet can be used. NB It is important that hay or grass is also available to provide indigestible fibre and stimulate gut motility.
Frances Harcourt-Brown, BVSc MRCVS