Rabbits

Chapter 2 Rabbits

Consultation and handling

Rabbits are prey animals and, therefore, may exhibit extreme anti-predator behaviour, such as jumping from the examination table. During a clinical examination, movements should be moderated and deliberate with loud noises avoided as these may startle the rabbit. The scent of potential predators such as dogs, cats and ferrets may be stressful to some rabbits so these should be removed by cleaning your hands, examination table and equipment as best as possible prior to examination.

Table 2.1 The rabbit: Key facts

Average life span (years)	5–10
Weight (kg)	1.0 kg (Netherland dwarf) to 10 kg (giant breeds)
Body temperature (°C)	38–39.6
Respiratory rate (breaths/min)	30–60
Heart rate (beats/min)	120–325
Gestation (days)	28–35
Age at weaning (weeks)	4–6
Sexual maturity (months)	4.5–9

Always weigh the rabbit at every consultation; weight loss may be the first occult sign of chronic disease such as dental disease. Most rabbits can be examined on a table with minimal restraint. If lifted, then one hand is placed beneath the chest while the other supports the back-end and legs. Many rabbits can have their perineum and ventral surface examined by gently turning them upon their backs, such that the rabbit is held and supported upside-down between the examiner’s chest and arm. The oral cavity can be examined with the use of an auroscope, although in the conscious rabbit this can never be regarded as a full oral examination.

Nursing care

Thermoregulation

This is one of the most crucial homeostatic mechanisms for rabbits (and other small mammals). They are susceptible to both hyperthermia and hypothermia (which acts as a general depressant and is also immunosuppressive). Body temperature is achieved and maintained at some cost to the rabbit, which must generate and maintain a high metabolic rate. However, their small size means that they have a large surface area compared with body mass with a consequent high potential for conductive, convective and radiative heat loss. In the conscious rabbit, heat loss is countered by a variety of mechanisms such as dense coats and subcutaneous fat (insulative layers) plus physiological methods – peripheral vasoconstriction/dilatation, piloerection and shivering. Behaviour also alters to either enhance or reduce heat loss. High respiratory rates secondary to stress can mean a significant evaporative heat loss.

Management of hyperthermia (see Systemic Disorders)

Management of hypothermia

1 Assess the rectal temperature of the rabbit. If in doubt, assume that the animal is hypothermic and that this should be corrected as soon as possible.

2 Applying insulation such as bubble wrap is often insufficient – collapsed or otherwise inactive rabbits are not generating heat and this may insulate it from a higher ambient temperature.

3 Place these animals on to a heat mat, on to which is placed an absorptive towel or other material to reduce the risk of localized burns.

4 Alternatives included heated operating tables, commercial warm air generators or incubators; ‘hot-hands’ (gloves filled with warm water) carry too high a risk of burns and cool too quickly.

5 Place insulative material over the animal and heat source.

6 Areas of the body where there is a high risk of radiative heat loss such as the pinnae or feet can be covered with aluminium foil to further conserve heat.

7 By either quickly raising the body temperature, or allowing the rabbit to maintain its core temperature with ease we remove the need for costly hyperthermic physiological processes, e.g. shivering.

Fluids

In small mammals the choice of fluid used is as indicated with other mammals. Venous access in the rabbit is via the cephalic, lateral saphenous and marginal ear vein (Fig. 2.1). Jugular cut down can be undertaken under general anaesthesia (GA), but may result in respiratory embarrassment. Fluids can be given i.v. either by bolus or by infusion.

Fig. 2.1 Correct placement of a catheter into the marginal auricular vein.

In hypovolaemic patients vascular access may be impossible and it may be better to consider either i.p. or i.o. administration. For i.o. it is relatively simple under GA to insert either an intraosseous catheter or a hypodermic needle into the marrow of either the femur (via the greater trochanter) or tibia (through the tibial crest). Fluids, colloids and even blood can be i.o. if necessary.

Nutritional support

Many rabbits are presented as emergencies after a prolonged period of ill-health that will have affected their food intake, e.g. suffering from undiagnosed chronic dental disease. These animals are often hypoglycaemic, so testing beforehand (a commercial glucometer is suitable) is beneficial, followed by i.v. or i.p. glucose to those cases identified.

Longer-term support can be given by syringe feeding commercially available food supplements, e.g. Oxbow Critical Care and Supreme Recovery Diet. The following caveats apply:

• Use a relatively wide-bore syringe as blockage at the correct concentration is common. Feeding a dilute mixture may be counter productive.

• Naso-gastric tubes can be fitted but these are prone to block.

• If the rabbit is very debilitated then choking/failure to swallow may occur; in these cases concentrate on parenteral fluids, dextrose and B vitamin therapy.

Analgesia

Table 2.2 The rabbit: Analgesic doses

Analgesic	Dose
Buprenorphine	0.01–0.05 mg/kg s.c., i.m., i.v. every 6–12 h
Butorphanol	0.1–1.0 mg/kg s.c., i.m., i.v. every 2–4 h
Carprofen	1.0–2.0 mg/kg s.c. or p.o. b.i.d.
Ketoprofen	1.0 mg/kg i.m. b.i.d.
Meloxicam	0.1–0.3 mg/kg s.c. or p.o. s.i.d.
Morphine	2.0–5.0 mg/kg s.c. or i.m. every 4 h
Pethidine	5.0–10 mg/kg s.c. or i.m. every 2–4 h
Nalbuphine	1.0–2.0 mg/kg i.m., i.v. every 2–4 h

Masking with volatile anaesthetics alone

The advantage of this technique is rapid recovery without the need to metabolize large amounts of drug, both of which can be important with rabbits that are catabolic, e.g. with chronic dental disease. Isoflurane appears to be less stressful for induction than halothane, based on lower corticosterone levels (González-Gil et al 2006).

• Oxygen can also be delivered via the nasal cavities – a small diameter catheter or tube is inserted into the ventral nasal meatus. Even moderate flow rates risk an explosive exit of such a tube! If necessary, a tracheotomy may need to be performed.

• Premedication with doxapram at 10 mg/kg i.p., i.v. or sublingually 5–10 min beforehand is occasionally recommended, but this will increase oxygen demand and the author finds it usually unnecessary.

Skin disorders

Normally rabbits have a soft, short undercoat covered with larger guard hairs. Rex breeds have short guard hairs that do not exceed the undercoat while Angoran breeds have very long guard and undercoat hairs. Lionhead rabbits retain the long hair around the head, neck and rump area.

Satin breeds have altered hair fibre structure.

Findings on clinical examination

Signs of skin disease:

• Typically hairs will be damaged. There may be areas of reddened and inflamed skin

• Oedema may accompany a cellulitis

• Ectoparasites especially Cheyletiella, Leporacarus and Psoroptes. Occasionally fleas (rabbit flea Spilopsyllus cuniculi (Pinter 1999), cat and dog fleas Ctenocephalides spp), lice, sarcoptic and Demodex mites and blowfly maggots. Cheyletiella may act as a vector for myxomatosis

• Ear mites (Psoroptes cuniculi): inflammation and pruritus of the pinnae (Fig. 2.2). Can spread on to surrounding face and neck

• Bacterial disease, typically Staphylococcus and Pasteurella species (Fig. 2.3). Pseudomonas typically linked to moist dermatitis under chin (blue fur disease)

• Occasionally due to Trichophyton

• Nodules, swellings and non-healing wounds

• Abscess. If these are around the mouth strongly suspect underlying dental disease

• Herpesvirus (circular, reddened skin lesions)

• Poxvirus – initial nasal discharge and fever. Followed by generalized formation of papules and nodules. Oedema of the face and perineum

• Cuterebra larvae

• Mycobacteriosis

• Myxomatosis (may see concurrent palpebral oedema, swollen pinnae, swelling of external genitalia and perineum)

• Shope papilloma virus (papovavirus)

• Shope fibroma virus (poxvirus)

• Acrochordon

• Lymphoma/lymphosarcoma

• Other neoplastic diseases

• Fibrosarcoma

• Squamous cell carcinoma

• Trichoepithelioma

• Basal cell tumour

• Apocrine adenocarcinoma (Miwa et al 2006)

• Excessively pronounced dewlap

• Some breeds selected for this

• More prominent in females

• May be site of recurrent moist dermatitis, especially Pseudomonas, where the dewlap is consistently moist, e.g. from water bowls.

Fig. 2.2 Ear mite (Psoroptes cuniculi) infestation.

Fig. 2.3 Severe bacterial dermatitis in a rabbit.

Fig. 2.4 Skin lacerations and subsequent dermal necrosis from fighting.

Investigations

1 Microscopy: examine fur pluck, acetate strips or skin scrapes to affected area and examine for ectoparasites

2 Examine material from ear canals for Psoroptes cuniculi

3 Examine teeth. Rabbits with dental disease may have difficulty grooming normally

4 Bacteriology and mycology: hair pluck or swab lesions for routine culture and sensitivity

5 Fine-needle aspirate followed by staining with rapid Romanowski stains

6 Biopsy obvious lesions

7 Ultraviolet (Wood’s) lamp – positive for Microsporium canis only (not all strains fluoresce)

8 Routine haematology and biochemistry

9 Serology for Treponema cuniculi titre

10 Endocrine analysis (see Endocrine Disorders)

11 Normal plasma thyroid level: 22 nM/L (Hulbert 2000)

12 If barbering suspected, examine hair under microscope to see if chewed; separate from other rabbit; supply extra hay.

Management

1 Rabbits with dental disease, or those that have had incisor extractions are unable to groom and will require regular grooming by their owner.

2 Routine and regular examination of the perineum of pet rabbits is essential. The presence of caecotrophs adhered to the perineum will encourage myiasis (see Failure to Caecotroph).

Treatment/specific therapy

• Treat for any ectoparasites

• Ivermectin at 200 μg/kg or as topical application (Xeno 450, Genitrix) works well for mites such as Cheyletiella, although treatment should be continued for greater than 6 weeks (life cycle = 5 weeks). Also for myiasis

• Imidacloprid (Advantage, Bayer) applied as a 40 mg ‘spot-on’. Can be applied weekly for lice and myiasis

• Permethrin applied as either a dusting powder or shampoo

• Initial treatment involves clipping of the fur and cleaning the affected area, with manual removal of maggots plus flushing with a dilute chlorhexidine or povidone-iodine cleanser. Supportive treatment should be aggressive with therapy for toxic shock plus ivermectin or imidacloprid to kill any maggots or emergent larvae that cannot be removed

• The underlying cause of the caecotroph accumulation must be addressed (see Failure to Caecotroph) and regular perineal inspection and cleaning, plus protection from exposure to flies is crucial in preventing the condition

• Topical cyromazine (Rearguard, Novartis) applied as a 6% solution topically every 6–10 weeks as a preventative for myiasis

• Cuterebra larvae: either remove via the breathing hole, surgically or by using Ivermectin at 200 μg/kg or as topical application (Xeno 450, Genitrix)

• Bacterial dermatitis and cellulitis

• Topical and parenteral antibiotics

• Cleaning with chlorhexidine solution may be beneficial

• Surgical removal of abscesses. Draining and flushing of rabbit abscesses rarely works

• Bites and lacerations

• Clean and debride well. Prone to infection so may be better to surgically excise the lesion and heal by first intention

• Covering broad-spectrum antibiosis

• Poxvirus, Shope fibroma virus

• Supportive treatment only; usually spontaneously regress

• Shope papilloma virus

• Can trigger warts especially on eyelids and ears

• Consider surgical resection as may eventually become carcinomas

• Spread by insect vector so anti-ectoparasiticidal treatment important adjunct

• Dermatophytosis

• Griseofulvin at 25 mg/kg once daily for 4 weeks

• Miconazole/chlorhexidine (Malaseb, Leo) shampoo – bath once daily

• Itraconazole at 5.0 mg/kg s.i.d. for 30 days

• Treponema (Rabbit syphilis)

• Responds well to penicillin at 50 000 IU given as once weekly for 3 weeks. In view of slight risk of inducing an enterotoxaemia, where possible always have serological test done first

• Tetracyclines and chloramphenicol can also be effective

• Lymphoma/lymphosarcoma

• See Systemic Disorders

• Surgical debulking, resection or euthanasia

• Accessible cutaneous tumours can be treated by injecting cisplatin directly into the tissue mass on a weekly basis as a debulking exercise

• Dewlap dermatitis

• Clean with chlorhexidine solution

• Dewlap resection.

Respiratory tract disorders

Rabbits are obligate nasal breathers. The back of the pharynx is comparatively small and is occupied by the main body of the tongue, preventing easy visualization of the caudal pharynx.

Investigations and management

• See Differential Diagnoses for Respiratory Disorders

Treatment

• See also Differential Diagnoses for Respiratory Disorders

• Poxvirus – initial nasal discharge and fever. Followed by generalized formation of papules and nodules. Oedema of the face and perineum. Self-limiting.

Dental disorders

• The permanent dental formula of the rabbit (Fig. 2.5) is:

Fig. 2.5 A diagram of a rabbit skull showing position of teeth and track of nasolacrimal duct.

Permanent dental formula of the rabbit

Investigations

a Lateral, DV views of skull. Note skulls often appear osteoporotic. Probably due to an atrophy of disuse but has been linked to hypocalcaemia

b Left and right lateral oblique views of skull to allow assessment of individual tooth roots. Any divergence of maxillary or mandibular tooth roots away from each other suggests abnormal root elongation (Figs 2.9, 2.10)

c Contrast study on nasolacrimal ducts

3 Check patency of nasolacrimal ducts (Fig. 2.11)

4 Routine haematology and biochemistry

a Concerns that rabbits with dental disease are hypocalcaemic are ill-founded. Calcium levels are readily responsive to dietary levels and calcium status is monitored with ionized calcium (total calcium 3.0–4.0 mmol/L; ionized 1.57–1.83 mmol/L)

5 Culture and sensitivity

a Aerobic and anaerobic culture of abscesses

7 Examination of oral cavity under GA

8 Biopsy (osteosarcoma).

Fig. 2.8 Buccal tilting and overgrowth of the upper first premolar.

Fig. 2.9 Right lateral oblique skull showing osteolysis around the root of the left first mandibular premolar associated with a tooth root abscess; there is also overgrowth of the second premolar, first molar and incisor roots.

Fig. 2.10 Explanatory diagram of Figure 2.9.

Fig. 2.11 Fluorescein can be used to check nasolacrimal duct patency.

Tags: Exotic Animal Medicine A Quick Reference Guide

Aug 21, 2016 | Posted by admin in EXOTIC, WILD, ZOO | Comments Off

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