The BSAVA advises that all non-breeding rabbits should be neutered (ovariohysterectomy and castration respectively) soon after they attain sexual maturity.  The exact age varies with respect to breed, ranging from 4 - 6 months, or up to 9 months in giant breeds.
Pre-pubescent females are difficult to spay because of their tiny uterus and ovaries that can be hard to locate6. Therefore waiting until sexual maturity makes for an easier, and hence safer procedure, and the risk of unwanted pregnancy is minimal. Rabbits should ideally be spayed before maturity when large amounts of abdominal fat can complicate surgery.

Males can be castrated when the testicles have descended, usually around 3 ½ - 4 months of age. Attempts to neuter prior to this may require abdominal surgery which is more complicated. If neutered shortly after the testicles have descended, the risk of unwanted pregnancy does not appear to be significant.

There are some reservations about neutering, but most are not justified when examined more closely. Especial care and attention to anaesthesia technique is important. It is acknowledged that rabbits may constitute a higher anaesthetic risk compared to other species. Neutering may predispose to weight increase, but dietary management can control this. The BSAVA believes the benefits of neutering rabbits outweigh any potential risks that are involved with the procedure.

REASONS FOR NEUTERING RABBITS

· Prevention of pregnancy and unwanted litters.
· Prevention of uterine neoplasia. The likelihood of developing adenocarcinoma is the most important medical reason to neuter female rabbits.
· Prevention of other uterine diseases. These include pyometra, uterine aneurysm and endometritis.
· Prevention of pseudopregnancy. It is stressful for rabbits to go through nest building, milk production and aggressive protection of territory. This can make the pet very difficult to handle during this period and can progress to decreased appetite and gastrointestinal problems.
· Prevention of mammary disease. Both cystic mammary gland and mammary neoplasia can be prevented by early neutering.
· Reduction of aggression. Neutering shortly after sexual maturity may be beneficial in modifying hormonally related aggression, thereby reducing undesirable behaviour towards the owner, and making rabbits less likely to fight if kept in groups. Despite this, keeping two adult rabbits of the same sex together may be difficult if they have not grown up together. It is also important to realize that there are a number of possible motivations for aggressive behaviour and neutering may not always be beneficial or appropriate. Full investigation of the underlying motivation is necessary in all cases of undesirable behaviour before a treatment strategy can be selected.
· Prevention of undesirable sexual mounting behaviour by an entire male rabbit towards other rabbits, or cage mates of other species.
· Prevention of testicular disease.  Disease of the testicle is rare in the male rabbit, but it can occur. Most common are abscesses (often from bite wounds from other rabbits), haematomas and neoplasia.

EVIDENCE-BASED SUPPORTIVE INFORMATION

Uterine adenocarcinoma is the most common tumour of entire female rabbits, with reported incidence of 50 - 80%1,2,3,4 in animals of certain breeds (tan, French silver, Havana and Dutch)5 that are older than 4 years, although breeding history is not a factor. Over time, the endometrium undergoes progressive change including hyperplasia, which is associated with adenocarcinoma, as in humans.
Local invasion of the myometrium occurs rapidly and infiltration may extend to other peritoneal structures. More distant metastases to the lung, liver and sometimes brain and bone can occur within 1-2 years3.  Clinical signs in breeding females include decreased fertility, small litters and increased stillbirths. In pet rabbits, owners may notice haematuria or a serosanguinous vaginal discharge, cystic mammary glands, and later weight loss, depression and respiratory signs due to pulmonary metastases. Treatment is ovariohysterectomy with thoracic radiography to evaluate for metastases. If metastases are present the prognosis is extremely poor.
Mammary neoplasia is less common in this species, but when it does occur it spreads rapidly and is usually concurrent with uterine neoplasia. Cystic mammary glands are common and although a benign change, the excess fluid within the glands can be uncomfortable.

REFERENCES

Baba N, von Haam E: Animal model for human disease: spontaneous adenocarcinoma in aged rabbits. Am J Pathol 1972; 68:653-656

Ingalls TH, Adams WM, Lurie MB et al: Natural history of adenocarcinoma of the uterus in the Phipps rabbit colony. J Natl Cancer Inst 1964; 33:799-806.

Weisbroth SH: Neoplastic diseases. In Manning PJ, Ringler DH, Newcomer CE, eds. The Biology of the Laboratory Rabbit. New York, Academic Press, 1994, pp 259-292.

Greene HSN: Uterine adenomata in the rabbit. J Exp Med 1941; 73: 273-292

Pare JA, Paul-Murphy J: Disorders of the reproductive and urinary systems. In Quesenberry KE, Carpenter JW, eds. Ferrets, Rabbits and Rodents. Clinical Medicine and Surgery. Missouri, Saunders, 2004, pp183-193.

Harcourt-Brown F: Textbook of Rabbit Medicine, Oxford, Butterworth-Heinemann, 2002, pp57.

Approval:  Approved by Council 2007.