Information about spaying and neutering rabbits taken from UK Rabbit Welfare Fund website
Male rabbits (bucks) make responsive pets, but have the same drawbacks as tom cats if they're not castrated. Most are territorial and frequently spray urine, and aggression is a common problem. They will also have to live alone, which isn't fair on an animal that needs company. Neutered males are much happier and more relaxed. They can enjoy life without constantly looking for a mate and are less aggressive and smelly. Nearly all neutered males will stop spraying urine even if the operation is performed later in life.
Castration is a relatively minor operation which can be performed as soon as the testicles descend (10-12 weeks) although most vets wait until the rabbit is 4 or 5 months old, when the operation is easier to perform and the anaesthetic risk is reduced. The testicles are removed via the scrotum or lower abdomen.
Having female rabbits (does) spayed is even more important. Most females become territorial and aggressive from sexual maturity onwards (4-6 months). They have repeated false pregnancies, and may growl at, scratch and bite their owners as well as attacking other rabbits. Keeping two females together - even if they are sisters - can make things worse.
Spaying reduces and sometimes eliminates these behavioural problems. Spayed females are likely to live longer then their unspayed sisters. Up to 80% of unspayed female rabbits develop uterine cancer by 5 years of age. Females who are not spayed when young and in good health may have to undergo the operation in later life if a pyometra (uterine infection) or cancer develops, although usually it is too late and the cancer has already spread. Spaying is a bigger operation than castration. It's usually performed when the rabbit is at least 4 or 5 months old. The uterus and both ovaries are removed via the abdomen.