An Approach to The Anorexic Rabbit.
A history of anorexia is one of the most common clinical presentations in the pet rabbit.
The following article appeared in Vet360 Vol 02 Issue 05 and can be accessed via the linked text.
Posted on 14 Oct 2015
Elliott DL Dip Vet Nur BVSc, Bird and Exotic Animal Hospital, Onderstepoort Veterinary Academic Hospital, M35 Onderstepoort, Pretoria. dorianne.elliott@up.ac.za
HOW DO WE IDENTIFY THE ANOREXIC RABBIT?
Healthy rabbits graze almost continuously and will produce copious amounts of hard faecal pellets (up to 180) daily. Anorexia will result in a reduction of first the volume and then the size of the hard faecal pellets. A history of poor appetite is an early warning for the clinician that further diagnostics are indicated.3 Diarrhoea is also a common presenting complaint.
We often try to offer tempting food to rabbits during the clinical examination. A rabbit that shows interest in the food but then ignores it or mouths and then drops the food is often a rabbit with a painful oral condition. A sick rabbit presents immobile, hunched over and oblivious to its surroundings. Be aware that rabbits can initially sit immobile on the examination table, in the “freeze” response and then jump and kick explosively. A rabbit on the table should always be under control to prevent accidents.
Digestive Physiology:
The rabbit is an obligate herbivore and a hindgut fermenter. The digestive system is adapted to a fibrous diet. Digestion in the stomach and small intestine is similar to that of monogastrics. The ingesta reaching the hindgut consists mainly of fibre. This fibre can be divided into two portions: fermentable and indigestible fibre. Both are important for proper gastrointestinal function. The fibre that passes into the proximal colon is divided into two separate portions. Fibres of a greater length than 0.5cm are directed distally and are excreted as hard faecal pellets. These fibres stimulate healthy gut motility. Smaller particles are directed in a retrograde fashion into the caecum. This phase of colonic motility is named the “hard faecal phase”. The caecum functions as a bacterial fermentation vat and has a complex and delicate microflora. Bacteroides spp predominate in a mixed microflora including aerobic and anaerobic bacteria, both gram positive and gram negative. Small numbers of potential pathogens such as Clostridium spp may be present but are not harmful unless changes in caecal conditions allow their proliferation.
Volatile fatty acids are synthesised by the caecal microflora and absorbed as an energy source. The fermentation in the caecum reduces the fermentable fibre to a soft paste containing amino acids, enzymes, microorganisms and volatile fatty acids.
Following a circadian rhythm, usually in the morning and evening, the motility of the proximal colon reverses direction and the caecal contents are expelled and directed towards the anus. This phase is known as the “soft faecal phase”. The caecal contents are excreted as soft, odorous clumps of material with a thick covering of mucus. These caecotrophs are re-ingested by the rabbit directly from the anus and are further digested in the stomach and small intestine. The mucus coating protects the many beneficial bacteria from destruction in the extremely low pH (1-2) of the stomach.1
Sequelae of anorexia
Anorexia in the rabbit quickly leads to multiple metabolic derangements. Rabbits are unable to vomit and constantly produce saliva. During normal digestion water is also secreted into the stomach and proximal colon. Re-absorption of water occurs in the caecum and distal colon. For this reason any type of intestinal ileus or obstruction rapidly results in dehydration, electrolyte imbalances and distension of the gut with fluid cranial to the site of obstruction.
As mentioned previously, anorexia can also result in dehydration of the stomach contents forming a so called “trichobezoar”. Rabbits with a trichobezoar will benefit from oral fluids and potentially from liquid paraffin. It was previously believed that the oral dosing of pineapple juice helped to dissolve the fibrous mat, due to the proteolytic enzymes in the juice. More recent research indicates that it is likely the extra oral fluid that is making the difference.3
Early in the course of the illness rabbits may appear bright and alert but they are predisposed to the development of hepatic lipidosis. During periods of anorexia glucose absorption by the gut decreases and there is a decrease in the amount of volatile fatty acids produced by the caecal microflora. This results in hypoglycaemia which stimulates lipolysis as well as the mobilisation of free fatty acids from the adipose tissue. The liver utilises β−oxidation to metabolise this energy source and ketone bodies are produced. Rabbits do not have effective metabolic pathways to correct acidosis and are particularly susceptible to the effects of ketoacidosis. Triglycerides accumulate in the hepatocytes, further compounding the problem. Hepatic lipidosis occurs most readily in already obese animals.3
Liver failure and death are often the endpoint in the chain of events that begins with anorexia. Hypoglycaemia, disorientation and ataxia followed by profound depression may be seen in this terminal stage of the disease.3
HOW DO WE APPROACH THE CASE?
It is imperative to establish the underlying cause of the anorexia. A thorough clinical examination including oral exam, abdominal palpation, faecal examination and potentially the use of other modalities such as radiography and ultrasound is indicated. Abdominal auscultation may be used to evaluate borborygmus. Basic haematology and serum chemistries should be run.
One of the most common underlying causes of anorexia in the domestic rabbit is dental malocclusion. The rabbit has aradicular hypsodont teeth that grow approximately 2mm per week. Pet rabbits commonly develop dental malocclusion due to genetic factors, inadequate bone mineralisation (due to a calcium deficient diet or inadequate access to UV light) and inadequate wear of the teeth. A dental exam is a requirement for any rabbit workup. Sharp spurs commonly develop on the cheek teeth that cause pain on mastication and thus secondary anorexia and ileus.3
Rabbit dentistry is a speciality on its own so we will cover it only briefly here. Ad-lib access to high energy foods such as pellets often cause the rabbit to eat insufficient amounts of hay as they preferentially select out the most palatable food. The rabbit’s dentition is designed for a diet of hard grasses and the constantly growing teeth need to be worn down by the grinding mastication of hay. With inadequate wear, the cheek teeth become overgrown and develop sharp spurs which can cut the tongue or gums. The roots will also proportionately elongate which can cause exophthalmos, sinusitis and lachrymation. The rabbit will then, in a vicious cycle, be even less likely to eat fibrous foods. Eventually the pain causes anorexia.
Overgrown cheek teeth are corrected by burring them down to a normal flat occlusal plane. Rabbits that have developed this type of malocclusion should have their teeth re-evaluated regularly as repeated management is likely to be necessary. True diarrhoea is a serious condition, no solid faeces are produced and the rabbit is typically very ill. These animals need aggressive therapy in order to survive.
Common causes of true diarrhoea include intestinal parasites, sudden diet change and bacterial dysbiosis from incorrect use of antibiotics. Antibiotics including Penicillins (especially if dosed orally), cepalosporins, tetracyclines and clindamycin may commonly cause dysbacteriosis. Enrofloxacin, trimethoprim-potentiated sulphonamides and metronidazole are listed among the safer antibiotics.3
Owners often mistake uneaten caecotrophs for diarrhoea. These caecotrophs may be found in piles in the cage or may be found tangled in the perineal hair.
Soiling of the perineum will also predispose the rabbit to fly strike. Animals with caecotrophic disorders will typically still pass solid faeces intermittently and will be bright, alert and responsive, often with a good appetite.
Commonly, a gradual increase of good quality fibre (grass hay) in the diet will encourage caecotropy, improve gut motility, control obesity (which can make it impossible to assume the correct position for caecotroph ingestion) and make the gut flora more resistant to sudden stressors.1,3
Abdominal palpation and radiography may reveal a distended stomach with gas surrounding a firm (sometimes palpable) mass. Many normal rabbit stomachs contain hair ingested while grooming. In the past it was thought that gastric trichobezoars were a primary cause of anorexia in the rabbit.1,3
We now understand that the hard mat of fur and fibre sometimes palpable in the stomach is simply dehydrated normal stomach content and is a sequel to, rather than a precipitating cause of anorexia.3 Occasionally a rabbit (especially a long haired breed such as the Angora) will develop a true pyloric obstruction. Both gastric and intestinal obstructions are emergencies and typically present with an acute abdomen and a collapsed rabbit. Gastrointestinal surgery on the rabbit is fraught with complications and is considered a last resort. The stomach and intestines are thin walled and fragile and dehiscence of surgical incisions is common. Nevertheless, a truly obstructed animal will need aggressive surgical intervention.3
Excess carbohydrate reaching the caecum predisposes the rabbit to bacterial dysbiosis. This occurs commonly in young rabbits in commercial settings where concentrates are fed ad-lib at the expense of adequate fibre. The rabbits typically present a few weeks after weaning with severe mucoid diarrhoea, collapse and death.
HOW DO WE TREAT THE CASE?
Owners should be made aware of the severity and potential fatal outcome of a case of total anorexia and minimal faecal output in a rabbit. These rabbits should be hospitalised for intensive supportive care. Of primary importance is the maintenance of a positive energy balance to prevent excessive lipolysis and hepatic lipidosis. Tasty fresh greens should always be offered to the patient. Good quality grass hay is also needed.3
Anorexic rabbits often need assisted feeding in the initial phases of the illness. DO NOT wait too long. Rather begin syringe feeding approximately 10ml/kg of pureed vegetable baby food/soaked complete rabbit diet or Oxbow Critical Care formula for herbivores (most ideal choice) 4-5x daily.3 Naso-oesophageal tubes may be placed if necessary (8FG works well) but are only used in patients that resist syringe feeding. Most rabbits will need an Elizabethan collar with the NO tube and the stress of the collar as well as the limitations it places on movement and grazing are often counter-productive. Should we need to use a collar at our clinic, we trim it in such a way that the ears are unhindered and the rabbit has easy access to food. We do this by leaving larger flaps of collar laterally and trimming it shorter dorsally and ventrally.
Although the rabbit may not seem to be losing fluids via vomition or diarrhoea, a rabbit with anorexia and gut stasis should be considered dehydrated. Subcutaneous or intravenous fluids (depending on the level of compromise in the patient) should be administered. Lactated Ringers solution is a good choice.3 Daily maintenance fluid requirements are approximately 60ml/kg/day.
Analgesics are indicated as gas distension of the inactive bowel causes pain which further compounds the problem. Opioids such as Buprenorphine (0.03mg/kg bid) are regularly used and are reported to have minimal effects on gut motility. Non steroidal anti inflammatories such as Meloxicam (0.5mg/kg once daily) are also used for pain control.2 The use of motility stimulants is a hotly debated topic. Many claim (rightly) that the best stimulator of intestinal motility is long stem unfermentable fibre. Nevertheless, we find that Metaclopramide (0.5mg/kg bid) and Cisapride (0.5mg/kg bid) definitely have a place in our treatment protocol. Naturally prokinetics are contra-indicated in cases of obstruction.2
Probiotics have been anecdotally reported to be of benefit in cases of dysbacteriosis. Commercially available probiotics do not contain the normal gut flora of the rabbit but do not seem to be harmful. Caecotrophs can be collected from a healthy “donor” rabbit by placing an elizabethan collar to prevent caecotrophy (ingested) and can then be fed to the patient to re-colonise the caecum.2,3 Anti-ulcerogenics such as Ranitidine (5mg/kg p/o) and Omeprazole are indicated as gastric ulceration may occur rapidly in a stressed rabbit.2
It is important to house ill rabbits correctly. They need quiet quarters, away from possible predator species such as dogs. A bed of hay is often useful both as a good fibre source and as a familiar environment. A hiding box or a covered area should be offered. Rabbits naturally seek out dark, small spaces as retreats when they are frightened. A safe, walled-off area should be available for supervised grazing outdoors. Anorexic rabbits will often be tempted to take fresh growing grass before any other foodstuffs.