A number of practical and philosophical issues need to be considered when contemplating whether or not to neuter rabbits:

•   risk of anaesthesia to the rabbit

•   risk of inducing pain

•   risk of anaesthesia to staff

•   zoonoses

•   surgical and post-surgical complications

•   fighting and other behavioural issues

•   pregnancy and its potential complications (Figures 1 & 2)

Figure 1: A pregnant rabbit spay

Figure 2: An excised pregnant uterus

•   welfare considerations of unwanted rabbits.

Risks associated with anaesthesia of rabbits

Death rates associated with the general anaesthesia of rabbits are higher than for dogs and cats; although the risk in a normal healthy rabbit undergoing elective neutering is very low. There are many anaesthetic combinations which may be used in rabbits and the safest ones seem to be those that the vet or nurse is most comfortable using.

Reducing the anaesthetic risks

It is important to perform a thorough pre-op clinical examination, paying careful attention to the respiratory system, both upper and lower. Blood tests are rarely indicated in young healthy rabbits.

Reduce stress by gentle handling and by hospitalising away from predators, such as dogs, cats, ferrets, snakes and birds of prey, and ensure that food, water and hay are constantly available both pre- and post-operatively.

Choose an anaesthetic or combination that works well for you. My combination of choice is medetomidine (Domitor – Pfizer) at 0.1 ml/kg, butorphanol (Torbugesic 1% – Pfizer Animal Health) at 0.03 ml/kg and ketamine (Narketan 10% – Vetoquinol) at 0.03 ml/kg.

All three drugs are mixed in one syringe and administered intravenously through a catheter that is placed in either the marginal ear vein or lateral saphenous vein. If venous access is not possible then consider xylazine (Rompun – Bayer) at 5mg/kg im and ketamine at 25-30mg/kg im.

Another useful combination is fentanyl/fluanisone (Hypnorm – Janssen) at 0.2-0.3ml/kg im in combination with midazolam (Hypnovel – Roche) or diazepam (Hamelin Pharmaceuticals). Propofol (Rapinovet – Intervet Schering Plough) may also be used intravenously at 3-6mg/kg.

Wherever possible, intubate the patient using either the blind technique or visualising the larynx with a laryngoscope or otoscope. If intubation is not possible, then placing a snug-fitting mask over the nose is a useful option. With a tight fit, positive pressure ventilation can be accomplished.

Analgesia is critical. Consider the use of non-steroidal anti-inflammatories, such as meloxicam (Metacam – Boehringer Ingelheim) at 0.1-0.3mg/kg s.i.d. – b.i.d. or carprofen (Rimadyl – Pfizer) at 2-4mg/kg sc s.i.d. pre-operatively or at induction. Carprofen may also be given post-operatively at 1.5mg/kg per os twice daily.

Intravenous fluids, such as Hartmann’s solution (Animalcare Ltd), can be given as boluses hourly until the patient is fully recumbent.

Heat mats can be used and patients are also wrapped in foil blankets or bubble wrap. Make sure excessive amounts of fur are not clipped and that warm water is used for surgical preparation. Avoid the excessive use of surgical spirits. Post¬operative recovery should take place in a quiet warm place, away from predators. Gut stimulants, such as metoclopramide (Maxolon – Amdipharm) or ranitidine (Zantac – GlaxoSmithKline) may be used pre- or post surgery and every attempt should be made to encourage rabbits to eat as quickly as possible, post operatively.

Use of newer anaesthetic gases, such as isoflurane (Isoba – Intervet/Schering Plough) and sevoflurane (SevoFlo – Abbot Animal Health) seems to be associated with fewer problems than we previously had with halothane (Halothane-Vet – Merial).

Other risk considerations

Wherever possible, risks to staff should be reduced by intubating rabbit patients and employing proper scavenging of gases.

Pregnant staff may need to take special care, and the risk of zoonotic infections should be borne in mind – zoonoses include Encephalitozoon cuniculi, Escherichia coli, Salmonella spp., ringworm, fleas, Cheyletiella, Giardia, Toxoplasma gondii and Bordetella bronchiseptica.

There are no data available for complications following neutering in rabbits. There are, however, a number of complications which may potentially occur.

Surgical risk to female rabbits

Umbilical hernias

1   have seen one case of umbilical hernia following spaying (Figure 3). This consequence may be the result of poor surgical technique or inappropriate selection of types or size of suture materials. I use a continuous polyglactin 910 (Vicryl – Johnson & Johnson) suture in the mid-line. Materials such as polydiaxanone (PDS – Johnson & Johnson) or poliglecaprone (Monocryl – Johnson & Johnson) are also acceptable. Catgut should not be used in rabbits as it frequently causes adhesions.

Figure 3: Umbilical hernia

Infection

This appears to be quite rare but cervical stump abscessation may occur.

Wound breakdown

This is a fairly common complication and is usually caused by self trauma. The incidence is greatly reduced if adequate pre-operative analgesia is used and if this is combined with post-operative analgesia. Metacam is given pre- operatively and all spays are sent home with a supply of the product. An intradermal suture pattern is also useful because rabbits have a tendency to chew at their sutures. I have seen a few cases that have resulted in euthanasia owing to self-trauma with non-healing wounds.

Adhesions

Adhesions can be a problem in rabbits and I have seen cases of constipation caused by an adhesion across the colon, hydronephrosis and hydro-ureter caused by an adhesion across the ureter, as well as adhesions involving the gut. These may be more common than appreciated and may be the most significant risk to female rabbits.

Ileus

The incidence of ileus should be reduced with gentle tissue handling, appropriate use of analgesia and reducing the stress of hospitalisation and handling as much as possible.

Surgical risk to male rabbits Inguinal hernias

Inguinal hernias

Rabbits have an open inguinal canal. A closed technique should be used, where the tunica is not incised; or if it is, it should be closed or the inguinal canal made slightly smaller. Many people are unaware of this and I am sure that many open castrations are performed with apparently minimal complications. I have seen an inguinal hernia in a chinchilla, but never in a rabbit.

Infection

The scrotal wound may become infected.

Wound breakdown

I don’t place skin sutures, so wound breakdown is not an issue.

Poor operator technique

Gentle tissue handling and the correct selection of instruments with reduce tissue trauma and the risk of post¬operative pain and infection.

Risks of not neutering female rabbits

Unwanted pregnancies

Unwanted pregnancies are potentially stressful to does and may lead to dystocia, ectopic pregnancy and mummification.

Aggression

Aggression both to the owner and to other rabbits may lead to fights and the development of bite wounds.

Uterine pathology

Failure to neuter female rabbits may lead to venous aneurysms, hydrometra, pyometra, endometritis, cystic endometrial hyperplasia, uterine adenoma and uterine adenocarcinoma (Figures 4 & 5). About 80 per cent of rabbits, that reach six years of age, will develop uterine adenocarcinoma that may metastasise to the abdominal organs, lungs, skin, brain and bone.

Figure 4: Pyometra in rabbit uterus

Figure 5: Uterine adenocarcinoma in rabbit uterus

Unwanted young rabbits

The birth of unwanted young rabbits is often associated with welfare issues.

Risks of not neutering male rabbits

Testicular tumours

Testicular tumours are quite rare and include seminomas, interstitial cell tumours and testicular nephromas.

Testicular torsion

Testicular torsion is a possible – but rare – consequence of not neutering male rabbits.

Aggression

The same points apply to aggression as with female rabbits.

Unwanted pregnancies

It is better to neuter females than males in order to prevent unwanted pregnancies and, in my experience, there is very low risk. I don’t routinely recommend castration of males, unless the clients request it or there are problems with aggression or behavioural problems in house rabbits, or if two males are kept together.

Author

William G V Lewis

BVSc CertZooMed MRCVS

William Lewis qualified in 1988 in South Africa and worked as a military veterinarian for two years before moving to the UK. He has worked in a number of small animal practices, including two exotic referral centres. His current job is at the Wylie Veterinary Centre in Essex.

• VOL 25 • No12 • December 2010 • Veterinary Nursing Journal