Updated November 2004
The vast majority of female rabbits develop cancer of the uterus (womb) in middle age, unless they are spayed.
The problem…. and that statistic
"80% of female rabbits get uterine cancer" … sounds familiar? That's because this statistic has become something of a mantra amongst houserabbit enthusiasts, keen to encourage rabbit owners to have their female rabbits spayed. To some people, the 80% figure sounds so dramatic, they assume it has been plucked from thin air for propaganda purposes.
But it hasn't. Nor is it a guess. In fact, the 80% figure comes from a study conducted more than 40 years ago (Greene, 1958). Although the information was published in the scientific literature, it doesn't seem to have been taken on board by vets and rabbit experts until the houserabbit movement gained momentum in the 1990s.
So how did this astonishing fact get overlooked for a whole generation, before being brought to prominence by the Americans in the early 1990s?
With the benefit of hindsight, we can perhaps make an educated guess. Firstly, knowing that most female rabbits would develop uterine cancer in middle age was all very well, but there was very little anyone could do about it. Improvements in rabbit anaesthesia and peri-operative care over the past few years have made routine spaying a reality, but not so long ago rabbit surgery was deemed so high-risk it was rarely performed electively.
Secondly, even if vets had been technically able to safely spay female rabbits, the client demand was not there. Rabbits were typically low-status, low-cost children's pets, or breeding/meat animals. Expensive surgery to remove the uterus of female rabbits would not have been contemplated for the former, and was irrelevant to the latter.
It was the houserabbit movement starting off in the USA that started a revolution - promoting the concept of pet rabbits as members of the family, suited more to adults than children, and deserving of high quality preventative health care. By the mid 1990s, the UK rabbit scene was on board, the uterine cancer statistics were in the arena, and the veterinary profession got on board, learning how to anaesthetize rabbits safely and neuter them routinely.
From an evolutionary perspective, rabbits are not designed for longevity. Wild rabbits are considered old at two years of age, and only a fraction pass beyond four. In short, wild female rabbits die long before uterine cancer develops and hence the disease is not a survival disadvantage to the species. It's not known exactly why the uterus of a female rabbit is programmed to self-destruct in this way. Presumably it's the penalty paid for high levels of circulating hormones earlier in reproductive life (rabbits are programmed to breed, well, like rabbits!) and the way uterine tissue responds to these hormones.
The type of cancer we are talking about is an adenocarcinoma - a malignant tumour of glandular tissue. It is an aggressive type of cancer, that tends to metastasise (spread) to other parts of the body, especially the lungs.
Uterine cancer is the commonest cancer of rabbits, and is the end point of a gradual process becoming much more common with increasing age. The classic study (Greene, 1958) which is so widely quoted in houserabbit circles showed 4% of does had uterine cancer age 2-3 years of age, rising to 80% at 5-6 years. It doesn't make any difference whether the doe has been bred from or not (Adams, 1962) or what breed she is.
Commercial rabbit breeders are unlikely to retain breeding females long enough for uterine cancer to become an issue. But for "hobby" rabbit breeders - many of whom keep favourite older does - uterine cancer can have an impact upon breeding performance.
Breeding females who develop uterine cancer "invariably" have a history of reproductive disturbance in the 6-10 months prior to the tumour becoming detectable by palpation. Typical problems are reduced litter size, stillborn litters, and does deserting their litters. Dystocia (difficulty giving birth); retaining fetuses in utero; abdominal pregnancy; and fetal resorption are all more likely when uterine tumours are developing. The tumours are usually multiple and the growth rate varies widely. Some grow large rapidly; others remain small, but throw off metastases and spread to other parts of the body such as the lungs. The time from detection of the tumour to death from metastases ranges from 12 to 24 months.
It's worth mentioning that the original studies were in lab or meat rabbits - not pets. But vets in both Britain and America, spaying rabbits routinely over the past few years, report that they are finding abnormal uteruses in a high proportion of slightly older pet rabbits, confirming that the findings of these 40-year-old studies are just as relevant in pet rabbits today.
The next question is how to tackle the problems posed by this common and deadly disease.
Greene, HSN 1958 Adenocarcinoma of the uterine fundus in aged rabbits. Am J. Pathol. 68: 653-56
Adams, WM Jr 1962 The natural history of adenocarcinoma of the uterus in the Phipps rabbit colony. N. Med. Sci Thesis, Henry Phipps Institute, Univ of Pennsylvania, Philadelphia.
Percy, DH and Barthold, SW Pathology of laboratory rodents and rabbits Iowa State University Press 1993, pp 222-224
Manning, PJ; Ringler, DH; Newcomer Christian, P The Biology of the Laboratory Rabbit pp 262-266 2nd edition 1994 San Diego Academic Press.
This article was first written in 1998 by Linda Dykes MBBS (Hons) and Owen Davies BVSc MRCVS, and the authors wish to thank Sally Walshaw MA, VMD (then the American veterinary advisor to the British Houserabbit Association; now based in Canada) who kindly conducted the literature search necessary to compile this article. It was revised by Dr Linda Dykes and Judith Brown BVM&S MRCVS, in November 2004.
Copyright - Linda Dykes 2004
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