American Fancy Rat & Mouse Association

This article is from the Winter 1998 AFRMA Rat & Mouse Tales news-magazine.

Troubles With Tailless

By Nichole Royer

Taillessness is a true mutation that causes a severe alteration of the rat’s normal body structure. Ideally it results in a totally Tailless rat with a rounded rump. Unfortunately, this mutation often does not produce consistent results, and the animals can show a number of different physical results. Some of these are benign; others can cause a drastic negative impact on the animal’s life.

Though Tailless rats have been bred for a number of years now, until recently very few problems were noticed (at least here in Southern California). In the last year this has changed. More and more serious physical problems have been seen, so much so that many fanciers are questioning whether Tailless rats should be bred at all. Very little has been written on the problems encountered by Tailless breeders, a situation I am attempting to correct with this article. I am by no means an expert on the subject, and in this article I am simply reporting some of the situations I have seen, and those that other people have told me about. I would like to thank all the Tailless breeders who have shared their problems (and the way they dealt with them) with me. Please remember, each breeder must be guided by their own beliefs when faced with difficult situations such as many of those mentioned in this article.

Stub Tails

Stub tails are a natural by-product of breeding Tailless rats. Some Tailless litters will contain babies with a little piece of tail — a feature responsible breeders will breed to eliminate. Rats born with stub tails will produce babies with a “tendency towards” stub tails, so they should not be used in a breeding program.

Stub tails can range from a lump where the rat’s tail would normally start, to a thin, stiff, string-like tail an inch or two long. These tails are typically very thin, simply vertebrae covered with skin. When these stub tails are very short they seldom cause the rat problems, however, longer (sometimes curled) ones can get caught and break.

Some breeders dock stub tails when the rat is a day or two old. Since there are vertebrae in these stub tails, docking usually leaves a distinctive lump at the base of the pelvis which a vigilant judge will find. This is a disqualification on the show bench. Some breeders firmly believe in not docking these tails unless they cause the rat discomfort. This way the presence of a tail is noticeable and the rat will not accidentally be used for breeding.

Limp Tails
Limp Tailed Rat

These are tail appendages which lack vertebrae. They can range from a tiny flap of skin at the base of the pelvis, to an entire normal size tail with no vertebrae in it. A small piece of skin on the backside of a Tailless is fairly common. Some breeders dock these. Since there are no vertebrae, no one can tell. This leaves an ethical dilemma. The AFRMA Standard says that it is a disqualification for a Tailless to have “a small tail appendage or tail formation at the base of the body.” It also states that any animal which has been changed in any way “designed to alter their natural condition” will be disqualified. Docking certainly qualifies as altering the “natural condition” of the rat, so technically it is unethical. Author’s Note: You will notice that nowhere in this article do I support, encourage, or explain how to dock rat’s tails. For more information, please talk to your veterinarian.

At the other end of the scale is a rat who has a large tail appendage (1 inch or more) up to an entire tail which is lacking vertebrae. These rats have no way to move or control these “dead” tails and so the tails are in danger of being caught or damaged. They also make it difficult for the rat to get around. These rats are reported to be prone to urinary tract infections and have difficulty keeping their hind end clean. Some breeders simply find these rats special homes. Some dock the tails (please see your vet) and still others put the rats down. No matter what is done, these rats should not be bred as they will pass on a tendency towards this condition.

Rear Leg and Pelvis Abnormalities

Some Tailless rats are born with rear leg abnormalities. When this happens, often the back legs fuse to the pelvis. This leads to a rat who cannot walk normally, and often hops like a rabbit. Occasionally, a Tailless will have a leg structure which forces it to only walk on its heals, makes it toe in or out, or simply makes it wobble as it walks.

Limp Tailed Rat

At the far extreme of this condition is the rare cases where there is no attachment of the hind legs to the pelvis, and the rat has to drag its back end. I have personally seen one case of a Tailless rat being born completely without a pelvis, and there have been a couple of reports of tailed rats out of Tailless lines who have the same pelvic structure as a Tailless. They have a rounded rump, but also have a tail. The AFRMA standard says that “any sign of physical abnormality due to being Tailless, e.g. difficulty walking or climbing, skeletal problems, etc.” will disqualify a rat from the show bench. Most judges will interpret this as applying to any rat negatively affected by being Tailless.

Needless to say, the breeder who produces any of these problems has a serious and heart wrenching decision to make. They must measure the rat’s quality of life and decide if euthanasia is the best course of action. Needless to say, NONE of these animals should be bred. If they show up in a breeder’s stock, that breeder should take a serious look at discontinuing that line of animals.

Bladder/Bowel Problems

In Nick Mays’ article in the NFRS Handbook, he mentions that his Tailless was “messy in the rear.” This is a problem which is becoming much more common and noticeable in the U.S. Tailless. Some very normal appearing Tailless rats have a hidden problem. Everywhere they go they leave little dribbles of urine. This goes beyond marking, and is actually a lack of bladder control. Some also experience the same problems with their bowels. Urinary tract infections are not all that uncommon in Tailless, and there has been numerous incidences of bladder stones.

There is not much that can be done for any of these conditions, other than to have a veterinarian treat infections, etc., when necessary. Rats exhibiting these symptoms should not be used for breeding as they will also pass on a tendency towards this condition.

In Conclusion

By now you must be wondering “why on earth does anyone breed these rats if they have such horrible problems?”

In all fairness to the very special and knowledgeable breeders who love and promote these rats, I have to say that most of these cases are rarely seen. The only problem which is common is a nub or limp tail (under one-quarter inch long). This causes the rat no discomfort, and is simply annoying to the owner if they want to show their rat (it is a disqualification). All the other conditions I have mentioned are extremely rare, and the most extreme are isolated incidences.

Up until this last year we almost never saw Tailless rats with detrimental physical problems. Unfortunately, the last year has seen a dramatic upsurge in the number and severity of problems with Tailless. Fortunately, they have not yet appeared on the show bench, but much to our dismay they are appearing just about everywhere else.

I believe that a major contributing factor to this is that Tailless rats have hit the pet stores. Many people love these little guys, and I don’t blame them. These rats have wonderful, bouncy personalities and make great companions. Unfortunately, pet stores and some breeders are only “in it for the money.” They don’t care about the health or the quality of life of the animals they produce.

In order to breed Tailless, some inbreeding must be done. This needs to be approached with great caution. Due to the nature of these rats, breeding animals who themselves have problems will lead to babies who have problems. Responsible breeders take great pains NOT to let this happen, and discontinue whole lines if necessary to prevent it!

If you are planning on buying a Tailless as a pet, please do some research. Ask around, visit, and talk with every Tailless breeder you can find. For those people just starting out in the fancy, please consider not starting out with Tailless. Tailless rats are wonderful little critters, but they are not only difficult to work with, but also heartbreaking. They really are not a good variety for the novice. If your heart is set on Tailless, please do the research and be prepared. Don’t fool yourself. Don’t say, “It won’t happen to me.”


NFRS Handbook, 1989 edition.
The many Tailless Breeders who were kind enough to share with me their experiences. *

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Taillessness in the Rat
Tailless Rats
Breeding Tailless Rats

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Updated September 21, 2018