Male rabbits can be castrated at any age. If you have taken on young rabbits, it’s best to have them castrated as soon as their testicles descend (10–12 weeks), although take advice from your own vet – some may prefer you to wait a little longer.
The operation is fairly straightforward, and recovery time is quite quick, provided there are no complications. Some vets perform rabbit castrations via the scrotum and some via the abdomen.
If you have a young male rabbit castrated within a few days of his testicles descending into the scrotum, he won’t have the chance to become fertile, and he can remain with a female littermate or companion. If castrated any older, be careful. Male rabbits aren’t sterile immediately after castration (mature sperm may have already left the testicles and can live a surprisingly long time!), so keep him away from unspayed adult females for up to six weeks after his operation.
For females, the spay is a major operation. Her uterus and ovaries have to be removed via an incision in her abdomen. Females are sterile as soon as they have been spayed, but if they have a male companion, you need to check he is gentle with her until the healing process is well underway. If you think he might mount your female rabbit, keep them apart for a few days, where they can see and smell each other through a wire mesh.
Females can be spayed from a similar age, but the uterus is very small at this point, and an age of 16-20 weeks is generally preferred. Spaying a rabbit over approximately 9 months can be more challenging due to the amount of fat which surrounds the uterus and its blood supply, so not leaving it too late is best for her. Waiting until the classic 6 months risks her becoming pregnant and at least 1 unwanted litter.
The physical size of the rabbit is not usually a surgical challenge, but rabbits under 1kg become progressively more difficult to intubate, and so this weight is a useful cut-off to await before surgery, where possible (i.e. some rabbits will be barely 1kg at adulthood, in which case there is little to be gained by waiting past 20 weeks.)