CABBITS - WHY CATS CAN'T BREED WITH RABBITS
Copyright 1999 - 2005, Sarah Hartwell

It is possible to cross-breed some animals. You can get crossbreeds from wolves and dogs because they are genetically closely related. You can get crossbreeds from horses, donkeys and zebra because all of these are closely related (the offspring are mostly sterile). You can get crossbreeds from pet cats and some species of wildcat because they are closely related. But you can't get crossbreeds from cats and rabbits because they are unrelated and are genetically very different from each other. A cat is a carnivore with its whole body adapted to hunting and meat-eating. A rabbit is a herbivore with its whole body adapted to eating plants. Even if you got a very confused cat to mate with an equally confused bunny, their genes are incompatible so you won't get offspring.

Closely related species can hybridize (e.g. horses and donkeys produce mules) but cats and rabbits are too distantly related. Their genes carry the code for very different structures e.g. a long vegetarian-adapted bowel in a rabbit and short obligate carnivore bowel in the cat. Even if a cat was mated to a rabbit and the egg was fertilized, it would die after a few cell divisions when cell differentiation occurs (when it starts to build the structures of the body) since the cat genes and rabbit genes give conflicting instructions and the embryo cannot work out what sort of creature to build.

Digestive System Differences

Herbivores evolved a gut to cope with the plant material cellulose.  They produce an enzyme (cellulase) to digest this and have a long intestine which gives plenty of time for cellulose to be digested. Despite this, rabbits pass soft, partly digested faeces which is eaten straight from the anus.  This is digested a second time, finally producing the familiar hard, almost odourless rabbit droppings.  Cats are carnivorous. They cannot produce the cellulase and cannot extract any nutritional value from grass.  Cats will eat small amounts of grass and other plant material as an emetic or as roughage; it is either vomited up or passes through their gut undigested.  Despite its long gut, a rabbit must process its food twice to extract enough goodness from it. The cat, with its short gut, cannot digest grass.  Cats are referred to as obligate carnivores because of their complete inability to digest plant material.

 

Diet

Stomach

Small Intestine (Ileum/ Jejunum)

Caecum/ Appendix

Large Intestine (Colon)

Stools

CAT

Obligate carnivore

Medium size

Short, relatively wide

Poorly developed or vestigial

Short

Moist, foul-smelling.

RABBIT

Herbivore

Large

Long

Medium to large size

Medium

(1) soft, re-ingested
(2) dry, compact, odourless

 

Mating and Gestation Differences

To start with, cats and rabbits have different mating habits. Female cats are induced to ovulate by the barbs at the end of the tom's penis. These barbs scratch the female cat's vagina as the tom withdraws after mating; this scratching is what causes an egg to be released by the female's ovaries. Male rabbits have smooth penises i.e. no barbs. Even if a sexually frustrated rabbit mated a female cat, the smooth penis means no stimulation of the female so she does not ovulate. No ovulation means no eggs for the rabbit's sperm to fertilize. One explanation from cabbit-believers is that the female cat must mate with a tomcat immediately before or after mating with the rabbit in order to ovulate. Even if she had already ovulated (from mating with a cat a few moments before or after), the cat and rabbit genes are incompatible and cannot form an embryo; any offspring will invariably be due to the prior or subsequent mating with the tomcat.

All but 4 of the cat species have 19 pairs of chromosomes while the rabbit has 22 pairs (38 chromosomes in cats, 44 in rabbits). The South American Geoffroy's Cat, Oncilla, Margay and Ocelot all have 18 pairs due to a fusion of two chromosomal pairs. Only genetically similar animals (same number of chromosomes) can hybridize. The gestation period of the rabbit is 30-31 days. The gestation period of the domestic cat is approximately 63 days. This is not a "similar gestation period" - the cat's gestation period is double that of the rabbit.

Genetic Differences

Michael Onken of the MadSci Network writes that there has never been a successful cross between a cat and a rabbit. The production of a hybrid mammal requires a great deal of genetic sameness (not just similarity) between both parents and even then the offspring are often sterile or stillborn. A viable cross between creatures as different as a cat (carnivore) and rabbit (lagomorph) is impossible without extensive genetic engineering. That sort of genetic engineering is still decades away. The closest modern science has come to this is with "hybridomas". Hybridomas are cells formed by fusing a normal cell with a tumour cell to create a hybrid cell which can multiply in the laboratory, but which cannot build a whole new creature. After the cells fuse, the hybridoma randomly ejects its redundant chromosomes.

Researchers have successfully made mouse/rat hybridomas (both are rodents) and have tried more exotic combinations. The closest they have come to a cabbit is a rabbit/hamster hybridoma (lagomorphs and rodents are closely related). The only other way Onken could think of to produce a cabbit, would be to surgically alter either a cat or a rabbit, though this would still not be a cat/rabbit hybrid.

In 2002, Chinese scientists attempted to use rabbits as surrogate hosts to cloned panda embryos (newborn panda cubs are about the same size as rabbit kits). They introduced panda DNA into rabbit ova (eggs), but none of the 2300 embryos resulted in pregnancy. They then tried using cats as surrogates. 21 cats were implanted with 10 panda-rabbit embryos and 10 cat-rabbit embryos (cat DNA in a rabbit ovum - to see if rabbit ova could implant in a cat uterus). None lasted past 48 days, compared with about 65 days for a normal cat gestation (Biology of Reproduction, vol 67, p 637). These non-viable cat-rabbit embryos were not "cabbit" hybrids as the nucleus only contained cat DNA and would have resulted in cat offspring that had rabbit maternal mitochondria. The experiment indicates that rabbit ova cannot develop in a cat's womb and that ova containing non-rabbit DNA don't develop in a rabbit's womb - so even if cat-rabbit hybrid embryos could be made in a test-tub and implanted in either a cat or a rabbit, the pregnancy would fail.

Despite the genetic impossibility, the cabbit myth has also been quoted as the "scientific" proof for a breed of cat called the Honeybear. Honeybears are a variety of Ragdoll cat. The original breeder claimed that Honeybears were created by genetic manipulation of the genes of a skunk, which were then "infused by injection" into the bloodstream of a cat. Genes simply don't work that way. At the current level of knowledge, the effects of gene therapy cannot be passed on to offspring.  However, as "proof" of genetic manipulation, the breeder cited the cabbit, which she said "ate like a cat and gave pellets like a rabbit." As well as cabbits themselves being genetically impossible, this dietary claim as anatomically impossible. A rabbit produces pellets because it eats a high-cellulose plant-based diet. It would be impossible for a carnivore to produce rabbit droppings!

Spurious Cabbit Claims

In spite of all the evidence to the contrary, the cabbit myth persists in popular belief. People desperately want to believe in such things as cabbits, unicorns and the tooth fairy. The appearance of alleged "cabbits" on the Johnny Carson show in 1977 led a lot of viewers to take the crossbreed story for granted. Neither Carson nor Chapman (the owner of the animal in question) were qualified to pronounce the animal to be a crossbreed. What was less well publicised was that the animal in question was examined by zoologists and found to be a cat with a pelvic deformity. It is human nautre to want to believe in something in spite of the facts and the evidence against it. Practical jokes, hoaxes and misguided (or fraudulent) individuals keep the myth alive. As if the detail in this article is not enough, I regularly receive emails saying:

"My cat once had 4 kittens, 2 of them had long back legs and hopped like rabbits.  Explain that!"

It's very simple and does not involve any rabbits!  Either both parent cats looked normal but carried the genes for the Manx condition.  Or a spontaneous mutation occurred which affected the spine, tail and legs.  Or the kittens developed abnormally in the womb and have a non-hereditary birth defect.

"Cabbits really do exist. In case you did not know a cabbit is a cross between a cat and rabbit. Supposedly the way this happens is that a male rabbit [....] will eagerly mount a female anything in heat, so a female cat, being in that state very receptive, will allow the union. The fact that the same number of chromosomes is involved as well as similar gestation period is supposed to have something to do with the possibility of offspring being produced...."

Or even that cabbits occur all the time in Ontario, or Texas, or that the correspondent personally breeds them because the only thing that has mated her cat, which isn't a Manx, is her pet rabbit and it isn't rocket science to know the offspring born 8 weeks later can only cabbits. When challenged, the correspondent is never willing to have the offspring DNA tested, claiming either taht they don't want publicity or that it's not rocket science and doesn't warrant scientific investigation. More worrying, these correspondents may be selling these kittens at a premium to unsuspecting purchasers.

Just as with the classic cabbit (racat) myth reproduced earlier, there are factual errors: rabbits and cats are two different species with different numbers of chromosomes and the cat's gestation period is double that of the rabbit.

Despite all of the evidence stacked against the cabbit myth, I received the following in response to the original version of this cabbit article. There are plenty of flaws in the writer's argument in favour of cabbits and the majority of cat breeders and vets who have seen this consider it to be a mistake or a hoax.

"In response to the VERY uninformed evaluation "Cabbits - What Are They?". In 1991,my own cat showed ALL the symptoms of pregnancy. She would eat only tomatoes, green beans and lettuce. Her belly grew larger as weeks went by and she sought out dark spaces for solitude. She exhibited all the signs of pregnancy, yet we could not figure out why. She was a COMPLETELY indoor cat and aside from our male bunny had NO sexual activity. However, she and Bruno had sex on a regular basis! We thought it was "Cute" and "Funny" at first. I mean, who would think a cat and a rabbit would go at it! I was in college at the time and I asked my bio professor about the likelihood of such a thing and he said however improbable it may be, the chromosomes are linked, and if they are not in a prey/predator environment, but domesticated together and there are no other sexual partners of the appropriate species available, propagation is possible. She had a baby. It was breech. We tried to help her with the delivery, however, unlike a "kitten", what she had was a good size larger and we had to actually pull it out. It suffocated, and the vet upon evaluating the situation, stated if any further pregnancies ensued, a caesarian would be required. For the record, the baby had folded lop ears like the father, a bunny nose, back legs like a rabbit and a tail that was very short (maybe half an inch) that curled up to it's back. So why don't you explain that know-it-all? I saw it. And better than that, plenty of others did as well."

Another one from the "triumph of stupidity over scientific research" stable (it may also be a money-making fraud, so anyone who thinks they are buying a hybrid from Ontario should have the animal DNA tested before handing over any money):

I just read your article on your web page and have to tell you that you are full of crap. Cabbits are real, I have had them and bred them and they are abundant in Ontario. No one has become famous, as you say about some vets in your article. It isn't rocket science and no one will be getting a Nobel for it. They are an accepted species in Ontario. I have pictures and can describe anything you want to know about them. They have soft fur like the rabbit, look like a cat except they have the hind legs of the rabbit, they are silent, don't meow and they kind of hop/walk. It is possible for some species to cross-breed, it just isn't much thought of. You really should research before you go spouting off. What the hell are your qualifications anyways?? I and my parents before me have been registered breeders of the CKC. I can also tell you that I can tell when 2 animals are mating and when 8 weeks later babies are born and the only 2 “going at it” was the rabbit and the cat. They are not manx and you really should have a few certificates on your wall before you judge those of us who actually know what we are talking about.

As is always the case, there were no photos and no DNA evidence. Far from spouting nonsense, I contacted several vets, scientists, cat breeders (including those with genetics qualifications) for information. This page includes a response from H J Baker, a professor and director at the Scott-Ritchey Research Institute at Auburn University's College of Veterinary Medicine - someone very qualified to discuss the matter. Any vet (or indeed a biology professor) encountering a genuine cat/rabbit offspring would have taken photographs, a blood sample (for DNA) and written articles for scientific journals. It would be worth a great deal of money. The dead offspring would have been examined, dissected and preserved for scientific study and no vet would miss an opportunity like that.

Another correspondent wrote that her neighbour had a real-life cabbit; a hopping cat with the front of a cat and the back end of a rabbit. Her brother in medical school concluded from a biology text book and concluded that it was genetically possible to a have a first generation cabbit, but that it would not breed and would probably suffer severe deformities and health problems since "the genes that make a rabbit a rabbit or a cat a cat have only one copy and there are several proteins in the body that may require an interaction between the two copies of genes from the same species."

This is true when closely related species hybridize (e.g. lions and tigers, horses and donkeys) but in cats and rabbits, the genes code for such different structures e.g. long vegetarian-adapted bowel in a rabbit and short obligate carnivore bowel in the cat, that they would not even manage to make a first generation hybrid. A cat and rabbit are just too different and even if an egg was fertilized, it dies after a few cell divisions and before cell differentiation since it cannot work out what sort of creature to build. Though the brother is in medical school, the knowledge required is specialised animal genetics knowledge which is not taught in medical school or in graduate level biology books!

The experts contacted pointed out that several factors show this to be a mistake or a hoax. As far as genetics doesn't make sense at all. It is not possible. You can only breed between species if there is some degree of genetic compatibility. Rabbits and cats are not only different species they are different genera as well. Rabbits are lagomorphs (often mistakenly called rodents). Although frustrated cats and rabbits have been observed to copulate through lake of more appropriate mates, no trained biology teacher would make the mistake of saying that two animals from different genera were genetically compatible.

Vets and breeders point out that eating only vegetables is a "normal cat pregnancy" is ridiculous since cats are obligatory carnivores. Cats fed on unsupplemented vegetables first go blind and later die due to not getting the correct minerals and amino acids in their diet. They will also have diarrhoea. No cat will voluntarily eat the diet described unless the owner forces it to.

One breeder came up with a plausible explanation for the events witnessed by the writer. A family member may accidentally have let the cat out and she got pregnant. The resulting kitten was deformed. A vegetarian diet might led to any other foetuses being reabsorbed before birth and to the remaining kitten being deformed. The family member would have been in big trouble about letting the cat out so they kept quiet and blamed the sexually frustrated male rabbit instead. I would call this a hoax and every vet and breeder contacted has called it a hoax. If it actually happened, well you can bet the vet would have had the foetus on display with papers written, studies done and lots of publicity. No vet would pass up the opportunity to document a genuine cabbit. The fact that it was not written up means that no vet wants to appear an idiot in the eyes of fellow animal professionals.

To confirm that my genetics knowledge is still up-to-date, I contacted a specialist cat forum about the cabbit claim. One of the forum members had seen a newspaper story about cabbits a month previously. She had contacted three vets about the spurious claim; one being a researcher in genetics at Scott-Ritchey Research Institute in Auburn, Alabama and does genetic research on cats. They provided the following responses to the question

".... is there any way at all that a cat and a rabbit could reproduce and have viable offspring? .....an effort to have 'expert' backup as I am writing a letter to the editor of a local newspaper with regard to a story it ran about a 'cabbit' ....the article is supposed to be a true report of a kitten that is a result of a breeding of a female cat by a male rabbit...I was sure that this was an impossibility but then I *have* been wrong before and just wanted some expert backup!"

Dr Susan Little, a Feline Diplomate DVM (i.e. specialist cat vet) in Ottawa replied "You'd be surprised how often this question comes up. No they cannot produce viable offspring, for a whole variety of reasons, not least of which is that the chromosomal complements of the two species are too different to have an egg and sperm unite and form a viable embryo."

H J Baker, a professor and director at the research centre of Auburn University's College of Veterinary Medicine, responded emphatically "The answer is simple, NO! The egg and sperm must match with respect to chromosome number and other factors shared only by members of the same species or closely related species (eg felids, equids). Even when two members of closely related species mate, there may not be conception or other problems arise. For example if horses mate with donkeys (two equids) the resulting "mules" are infertile. The term mule actually means infertile. … it is more believable that the mom rabbit adopted and nursed an orphan kitten."

A third vet with more than 25 years experience of cats, rabbits and other small domestics simply stated that the cat/rabbit hybrid was an impossibility.

One cabbit-believer claimed that people didn't publicise the information for the cabbit's safety and found this "scary", but the truth of the matter is that whatever is living next door is most likely a Manx cat! The fact that neither the cat nor its owner is documented in veterinary journals, and the cat's vet has not published papers on his client's pet, shows it is not a hybrid. The fact that no genetic analysis exists tells me that people WANT to believe the cabbit myth as it is a more romantic idea than the reality of a slightly deformed cat. Having claimed the pet to be a cabbit they are then scared of a genetic analysis since it quickly disproves their story!

Some visitors to this site desperately want cabbits to exist in spite of the biological and genetic evidence. Some insist that cabbits have been born, but are genetically defective and malformed and do not survive. None have been able to provide scientific evidence (items in reputable scientific journals, DNA analyses) to support their claims. Their claim may be based on the lethal nature of the Manx gene. When two tailless (rumpy) Manx are bred together, some of the offspring inherit 2 copies of the Manx gene. This results in grossly deformed embryos, most of which are reabsorbed, though some may be born dead. The claims of "hushed up" dead cabbit embryos falls into the category of conspiracy theory.

IMPORTANT NOTE

I often receive emails from people saying "I have personally seen a cabbit" or "I have a cabbit" or "cabbits are born but don't survive" or even "My vet says it is a cabbit". What you have is a cat with one or more of those traits which make it resemble a rabbit and a vet with a sense of humour or who watches too many cheap talk shows.

Absolutely the ONLY proof of a cabbit existing in real life is independently verified DNA evidence to prove that the animal you have is a hybrid. If the DNA evidence was real, it would be big news (as big as cloning) and would be printed in scientific journals, nature journals and veterinary journals. This site will not consider any claims of genuine cabbits unless supported by material from reputable, respected scientific journals

Ask yourself these questions: Do you really, honestly believe that any vet would pass up such an opportunity to become famous, and possibly wealthy, from finding a real-life cabbit? Are you so sure of your claim that you are prepared to have a DNA analysis done on your cat or kittens? Do you have independent scientific evidence from at least 2 accredited laboratories and qualified professional genetics researchers (not hobbyists) to support your claim? Have the results been published in a recognised scientific journal? If not, all you have is a delusion.

Regardless of the genetic impossibility, it seems that people want to believe in cabbits (especially with the cabbit characters in popular Japanese anime) just like they want to believe in the Easter Bunny - and they will continue to believe in mythical creatures despite all evidence to the contrary.

MESSYBEAST.COM CABBIT INDEX

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