by Guen Bradbury, Rabbiting On Veterinary Adviser

At RWAF, we advise that all rabbits should be neutered to prevent unwanted litters and unwanted sexual behaviour, such as mounting and spraying. However, even after neutering, many male rabbits will still mount their companions and many female rabbits will continue to dig large holes (some males also). Owners often worry that the rabbit wasn’t neutered successfully, but these behaviours are not just driven by hormones from the ovaries or testicles. In this article, I’ll explain what sex-specific behaviours are, when they start and why they happen. I’ll describe what neutering does and why it doesn’t prevent all of these behaviours. Finally, I’ll advise on how to manage these behaviours.

What are sex-specific behaviours?

Sex-specific behaviours include scent-marking behaviours, such as spraying urine on other rabbits, people, or objects and leaving dry faecal pellets around their enclosure to mark territory. They also include courtship behaviours, such as circling around people or rabbits and making a humming sound. Finally, they include mating behaviours – mounting rabbits or people.

When do sex-specific behaviours start?

Sex-specific behaviours start at puberty. The testicles of male rabbits descend around 10–12 weeks of age (female rabbits reach sexual maturity around a month later), and both sexes start to show sexual behaviours.

What drives sex-specific behaviours?

These behaviours are driven by the sex hormones oestrogen and testosterone. When an animal reaches puberty, the part of the brain called the hypothalamus starts producing more of a hormone called gonadotrophin-releasing hormone. These gonadotrophin-releasing hormones tell another part of the brain, the pituitary gland, to release hormones called gonadotrophins. These gonadotrophins then act on the ovaries or testes (the gonads) and make them produce more oestrogen or testosterone. Rabbits are seasonal breeders – when the days start to get longer in spring, their brains start to produce more gonadotrophin-releasing hormones, and this seasonal rhythm drives seasonal sexual behaviour.


But these gonadotrophins don’t only act on the ovaries or testes – they also act on the adrenal gland (the gland that most people know produces adrenaline). The adrenal gland releases a variety of different hormones, two of which are oestrogen and testosterone. This means that these hormones don’t just come from the ovaries and testes.

What happens when we neuter a rabbit?

When we neuter a rabbit, we remove the sperm and egg-producing organs. When a vet neuters a male rabbit, they make an incision in the scrotum and remove both testicles, the blood supply, and some of the spermatic cord (though not all of it, which is why male rabbits may still be fertile for 4-6 weeks after neutering). When a vet neuters a female rabbit, they make an incision in the abdomen and take out both ovaries. Some vets will remove the uterus as well, though the benefits of this are debated. In the UK, most older vets will try to do ovariohysterectomy but it can be hard to get right down to the cervix, so in practice, many are ovariectomies. Additionally, given the adhesion risk in rabbits, the increased pain with a more complex surgery, and the increased surgical time, many sources now recommend ovariectomy rather than ovariohysterectomy in companion animal species – providing the ovaries are removed, there is no increased risk of stump pyometra.

Why do some behaviours persist after neutering?

Not all sex hormones are produced by the ovaries and testes, so when we remove these, the adrenal gland will continue to produce some. Although the rabbit cannot produce sperm or egg cells, the adrenal gland can still produce some sex hormones – especially during the spring. Some rabbits will show more sexual behaviours than others – this seems to be because some adrenal glands produce more testosterone than others, and in some rabbits, the adrenal glands may increase production of testosterone when the testes are removed. Neutered rabbits have higher levels of sex hormones than neutered animals of other species (like ferrets, cats, and horses) – this would indicate that the adrenal gland produces a fairly substantial amount of sex hormones (House Rabbit Society, 2004).


These persistent levels of sex hormones in neutered rabbits explain the sex-specific behaviours that we see. This may also explain why male–female pairs are easier to bond and less likely to fight than single-sex pairs – the sex hormones cause different motivations and need for resources between male and female rabbits, and so there is less competitiveness between rabbits of the opposite sex.


Neutered rabbits may show social, sexual, or even mild aggressive behaviours in the spring. Females may dig new burrows. Rabbits may become more aggressive to their companion rabbit or to people – they may chase and mount them more and may ‘chin’ to mark their territory more frequently.


Very rarely, sex-specific behaviours may indicate incomplete removal of the ovaries or testicles. Neutering of a male rabbit is a simple procedure and it is extremely unlikely that part of the testicle is left behind. If the rabbit has a retained testicle (it has not descended into the scrotum), then the vet will discuss this with you. Sometimes, a bit of ovarian tissue may be left behind in a female rabbit – speak to your vet if you see behaviours such as fur-plucking from the dewlap in your neutered female rabbit.

What can we do about sex-specific behaviours?

Sex-specific behaviours in neutered rabbits rarely cause a serious problem. Many bonded pairs may have more disagreements in spring and early summer. There will be more mounting and chasing but as long as there is no fighting this should settle down in a few weeks. If serious fighting breaks out, they’ll need to be separated, given time to calm down and then carefully reintroduced once their hormones have settled down. This may take several weeks. Try not to bond new rabbits at this time of year as there is a higher chance that they may fight – if you need to, then keep a closer eye on them than usual.


Keep a close eye on your rabbits at this time and act immediately if you see any fighting or signs that a fight may have happened (scattering of fur, blood or wounds on one or both rabbits). Give them plenty to do in their home to keep mentally and physically active. Allow them the freedom to express their normal behaviours of digging, foraging, running and jumping.

Conclusion

In conclusion, the majority of neutered rabbits will continue to show some sex-specific behaviours because neutering doesn’t remove all of the sources of these hormones. Neutering can reduce the severity of unwanted behaviours and prevents unwanted litters. The remaining sex-specific behaviours give your rabbit some of her or his unique personality!

Reference:

https://rabbit.org/sex-hormones-in-altered-rabbits/