It is recommended that all rabbits not intended for breeding are neutered, for the following reasons:
Prevention of Pregnancy
Prevention of Uterine Cancer. This is the most compelling medical reason to neuter female rabbits. Up to 80% of female rabbits over the age of 2 years may develop this disorder.
Prevention of Other Uterine Disease, such as infection and bleeding.
Prevention of False Pregnancies. Although this is not medically harmful, it can be very stressful for the rabbit who goes through all the motions of being pregnant including nest building, milk production and aggressive protection of her territory. This aggression can be taken out on the owners and other rabbits.
Prevention of Aggressive Behaviour. Both male and female rabbits can display aggressive behaviour when they reach sexual maturity.
Prevention of Urine Spraying. Both male and female rabbits can spray urine on vertical surfaces to mark their territory.
Prevention of Testicular Disease.
The best age to neuter is 4-6 months of age, but slightly older in giant breeds.