Discussion paper on the facts of the NBT
information on the Bobtail Gene
a back up copy, copied directly and completely from http://www.imgnr.com/at_art__ii.htm
The Bobtail Trait in Australian Shepherds – Part II: Genetics of the Tail
by Gemi Sasson-Brickson, M.S. Biology
Reprinted from the May-June 2005 Aussie Times..(This is the second of a series on the Bobtail Trait in Australian Shepherds, written as an educational piece in relation to the Study on the Inheritance of the Natural Bobtail in Australian Shepherds. The previous article dealt with docking regulations and views in various countries. This article addresses the genetics of tails in general and various health aspects related to, or considered to be related to, tail length. This article also contains a couple of interviews about parallel studies in other breeds that may give us clues to a possible mode of inheritance. The final article will contain information on objectives of the NBT study, as well as some preliminary findings.)
I must admit when I embarked on this study, I attempted to remain as objective as possible. But always, some of the more extreme beliefs – that the breeding of naturally bobtailed animals would inevitably invite genetic disaster – disturbed me. I had begun my own breeding program with a very short bobtail bitch, Ch. Lineriders Imagineer of Dakota CD, who was at one time bred to another bobtail dog, Ch. Zeller’s WinterHavens Rusty. This produced our Ch. Katzenjammer Kid of Imagineer CD, STDs, who was herself a very short bobtail and produced several bobtails during her life. Limited as our own experience may have been, all those pups were healthy and the bitches tended to produce larger litters. But were there other cases out there that might refute my personal experience? If specific spinal defects were present in only bobtail animals, this would indeed point to adverse effects associated with the gene. However, if such defects existed equally in full-tailed individuals as well, this would indicate those effects are not related to the NBT gene, but present universally. And was litter size affected by the breeding of bobtailed individuals? Never being one to guess at things, I set out to collect data from a variety of bloodlines, from litters with all full tails, to those where NBTs were present. This would give some indication of litter sizes, what percentage of pups were born with bobtails from which combinations of parents and whether or not any spinal defects might be present in exclusively bobtailed individuals.Other breeds and species might give us a broader understanding of bobtails and even tails in general. I will begin there for the moment, as I believe that the occurrences in other breeds or species may have been the source of some of the confusion about bobtails.
Distinctly, I remember the very first time the topic of bobtails in Aussies came up and was paired with an implication of spinal defects and the issue of Manx cats was mentioned – the inference being that if it was a problem for one species, it was so for another. Well, I happened to have been owned by some wonderful registered Manx cats in the past decade and so I actually joined a Manx discussion list briefly to pick their brains about the issue of taillessness (and yes, ‘cat’ people are a bit different from ‘dog’ people). Unfortunately, I didn’t save any of those correspondences, but I do want to quote a reference to the concerns that Manx breeders deal with. The following is from The Manx Cat by Marjan Swantek (T.F.H. Publications, Inc., 1987):“…Kittens that inherit the Manx gene (M) from both of their parents (MM) do not survive and probably die during the early stages of development in the uterus… Manx litters are usually smaller than those of normal cats… Therefore, Manx can never breed true… It is unclear whether the dominant Manx gene, itself, is lethal or whether it is not, but instead is closely linked to a recessive lethal gene.”
It is understandable, then, where a preconceived notion about bobtails in our own breed could arise from. According to Swantek’s book and other sources, defects in Manx, such as fused vertebrae, typically affect the spine and hindquarters and breeders are careful to either limit their rumpy (totally tailless) to rumpy breedings or avoid them altogether by breeding rumpy to tailed Manx. Just an interesting note, but Manx breeders pay close attention to the tail length at birth and record it. Tail lengths are called: rumpy (tailless), rumpy riser, stumpy and full tail – the latter two of which are routinely docked in America.Here again, I would like to advise the reader that while studying other breeds or species may give us clues about our own, it is inadvisable to assume that what is true for one breed or species is true for another, as varying genes and factors come into play. The Manx, for example, has a very different skeletal structure from most other cat breeds. One has only to view the silhouette of a Manx to see exactly where it differs from other cats – not only in the absence of a tail, but that its back is distinctly rounded, giving a shorter-backed appearance, and its forelegs are notably shorter than its hind legs. Our own white Manx looks very much like a rabbit when he is running through the tall grass, but make no mistake about it that he is every bit as fast as a normal cat.
While there do exist known inherited spinal abnormalities in Manx cats, what about another naturally short-tailed cat – the Japanese Bobtail? The Japanese Bobtail, as compared to the Manx, is a much leaner and somewhat longer-backed cat with a more level topline. The spinal and hindquarter defects that occur in the Manx do not exist in the Japanese Bobtail. In the Manx, the gene for short tails is a dominant trait, while in Japanese Bobtails short tails are recessive. All Japanese Bobtails are short-tailed and are therefore homozygous for short tails. They are never born with long tails, nor are they ever born totally tailless, as Manx can be. It is very typical for their tails to have bends or kinks in them and the tails can be as long as three inches.So in these two breeds of cats we have two different modes of inheritance for tails, two different body types, and two different situations in regards to health. Plainly put, their genetic make-up is different in some key ways, even though they belong to the same species. The study of genetics is a complex field with many variables and components.
While we have some very distinct differences then in these two breeds of cats, how many variations in tail inheritance might exist in dogs? One well-known resource for dog breeders is Malcolm B. Willis’s Genetics of the Dog (Howell Book House, 1989). In the ‘Tails’ section, Willis refers to several sources regarding tails and tail abnormalities: bobtails (what he calls ‘docked’), screw tails and kinked tails. While Whitney’s How to Breed Dogs (Howell, 1971) postulates that the kinked tails of some long-tailed dogs are the result of the bending of the tail while in embryo, Willis suggests that the condition may be genetic, due to a higher incidence of the anomaly in certain lines. Some breed standards (for breeds with tails of varying lengths) mention kinked tails as being a fault; thus, this condition does exist in long-tailed as well as naturally short-tailed breeds.Screw tails occur in breeds such as the Boston Terrier, French Bulldog, and the Bulldog. I came across a very interesting online article, “Spinal Abbreviation Related Anomalies in Bullbreeds”, regarding screw tails by Carol Hawke at a Canine Chronicles website. In this article, Hawke warns of the dangers that present themselves when breeding towards one particular extreme in skeletal structure – in this case the combination of screw tails and the selection for a shorter back, thus producing cramped or malformed spines. While this particular viewpoint may not appear related to the topic of our natural bobtail in Australian Shepherds, it again illustrates that there are many different types of tails in dogs and many other factors that influence the presence of deleterious genes, such as skeletal differences.
When I discovered an article by Anne Indergaard, entitled “Breeding Bobtails”, it was a little like finding a match in a dark cave after an eternity of stumbling around blindly. To summarize, after some of the European docking bans went into effect, Pembroke Welsh Corgi breeders in Norway decided to bring the bobtail trait back into their breed, because most of the gene pool there consisted of full-tailed dogs. They did this by importing bobtail Pembrokes from the U.K. and then very studiously recorded the results of various breedings and investigated health aspects in relation to the trait by x-raying individuals and maintaining extensive records on litters. Ms. Indergaard is a Corgi breeder, judge, member of the Board of Directors of the Norwegian Kennel Club and an editor and reporter for various dog publications, as well as being an English teacher. She shared her knowledge of the Norwegian Corgi breeders’ experience and results with me in an e-mail interview:
Question: When the docking ban went into effect in the late '80's, Pembroke Welsh Corgi breeders in Norway decided to import several bobtail PWCs from the U.K. You mentioned in your article that most Pembroke breeders in England had actually selected away from the bobtail because it was harder to dock and towards a longer, easier to dock tail. Thus the bobtail was uncommon, except for the Blands and Stormerbanks lines, and some of these bobtail dogs were imported into Norway. Since the pool of bobtail Pembrokes in Norway was at first very small, how did breeders go about breeding for the bobtail trait while continuing to works towards other qualities, such as overall type and structure? Since you were crossing bobtails to full tails, did the bobtail trait prove to be dominant?
“We bred the bobs to our best, keeping the bobtails for further breeding and then going back to the best we could find with a full tail. By not line breeding to the first imports, but being very much aware of the need to keep a wide gene pool, we were able to work towards other qualities once the tail was there. As the bobtail gene is dominant, you would know you had the gene if you had the short tail. So then you didn't have to worry about that any more, but could concentrate on whatever else you'd want to improve.
“After scientists at the genetic department of our university had located the gene for the bobtail in corgis, blood tests were made of all dogs from bob-to-bob breeding, and none were carrying the gene in double doze (none were homozygotes for bob), which should have been the case had there been any. Dr. Bruce Cattanach says that the double gene fetuses most probably got absorbed at a very early stage and didn't develop past the egg stage, but as in all litters eggs are reabsorbed, for one reason or other, this would not affect the actual litter size. Which the club statistics have proved. But this means that we can never expect to have a population of 100% bobtails. If a dog or a bitch carries only one gene for bobtail, you would expect half the puppies (statistically, over a large number of litters) to have bobs, the others full tail. For reasons not explained, we have now over the years got 60% bobs from bob-to-full tail matings. Bob-to-bob litters have statistically around 70% bobs.”
Question: What were some of the myths you had to deal with at first about bobtail breedings? How did the records kept by the kennel club in Norway prove or disprove these myths? Was there any effect on litter size when bobtail pups were present?
“One myth was that the bobtail gene led to deformities of the spine. An x-raying programme instigated by the corgi club and the kennel club proved that no such deformities existed. Another myth was that the bobtails had no hind angulation. To bust that myth, all we had to do was breed well angulated corgis with natural short tails. Which we did. Still another myth was that short bobtails lead to no anuses. Too silly to even do anything about. No corgi without anus was born in any litter, with or without tails.
“Yet another myth said that if you kept breeding for bobtail, they would in time get so short that instead of a stumpy tail you'd get a hole inwards towards the nerves of the spine. As if you could get a negative tail?? We have yet not been able to determine what decides the actual length of a bob, as the gene seems to say "full tail/not full tail", but it appears that those with a really short bob tend to give more really short bobs than those with half a tail. But those half tails can also produce really short ones and the other way around.
“The easiest myth to bust was that it lead to decrease in litter size. The club chairman, Olav Hedne, kept statistics of litter sizes, both before and after the docking ban and the bobtail breeding, and if anything, the litters got bigger, probably due to this being absolute outcrosses. Now we are back to normal litters – average 4-6 pups, if I am not mistaken.
“Some said that the bobtail gene was the same as the gene for kinky tails. As kinks can appear both in long and short tails, this cannot be so. Before the docking ban, no one thought much about kinks, but it seems the Norwegian corgi population haven't got that gene and neither have the later imports, so for us this has not been an issue, while in Finland they discovered the problem after the docking ban and had issued instructions to judges to disqualify dogs with kinky tails.
“The most serious myth, though, was that the bobtail was caused by a lethal gene. In as such as there has been no homozygote bobs born, this is probably true. BUT it is not lethal to anyone but the homozygote eggs. See above. Those pups born with a short tail is as healthy as the rest of their genetic makeup and life situation allow for.”
Question: Among Pembroke owners and breeders in Norway, is there any general preference for a long or short tail and why?
”The Pembroke standard says "Tail short, preferably natural", so as we all try to breed to the standard, of course we all prefer the short tails. This doesn't mean that we discard all the ones born with long tails, that would be throwing the baby out with the bathwater, but we will then use them with our bobs for future breeding. And we show them and if they are better specimen, they'll win with a long tail. This was not so in the beginning, as the judges needed time to get used to what a long tail does visually to proportions.”
An imperforate anus (also known as atresia ani) is a condition wherein the intestinal tract is incomplete. There may be an anus present, however it may be closed off somewhere in the intestinal tract. Or sometimes the intestinal tract is nearly complete, except that the anus has no opening to the outside. Pups may be born apparently healthy, but due to their inability to defecate, digested materials accumulate internally, eventually presenting a toxic situation and the pup dies, sometimes within days of birth, but some pups have been known to survive for a few weeks until the time that they were weaned from their mother’s milk and begun on solid foods. So why does this happen? In early embryonic development, there is a stage where the newly forming cells begin to indent, changing the shape of the embryo from something like a ball to a cup-shape. This indentation gives rise to the archanteron - the cavity that eventually forms the digestive tract. An imperforate anus is an embryonic developmental anomaly wherein the gastrointestinal tract simply does not fully form. Although this condition does occur in both full-tailed and bobtailed pups, it is uncommon, and therefore it would take a thorough investigation following several generations and related dogs to determine whether or not there is a genetic component to it and to what degree it is heritable.What about reports of spina bifida in Aussies? Is that related to the natural bobtail? Spina bifida is a congenital (present at birth) condition that occurs when during fetal development, the vertebral arches do not completely close and so the spinal cord, which would normally be enclosed and protected by the vertebrae, protrudes. This condition varies in degrees, from only being detectable by x-ray, to protrusion through the skin and exposure of the spinal cord resulting in severe deformity and paralysis. Most often, this condition occurs in the lower back (caudal area). It exists in such species as mice, cats, dogs (although in dogs, Bulldogs have a much higher incidence of the condition), sheep, cattle, horses and humans. In humans, spina bifida has been associated with a deficiency in folic acid during pregnancy and also with environmental influences such as certain chemicals. In animals so far, dozens of genes have been associated with neural tube defects – studies on mice looking exclusively at neural tube defects have been done. Without further study in bobtailed dogs, one cannot say clearly whether or not the bobtail gene in our breed is related to an increase in spina bifida.
So far, I have addressed different tail types and various health concerns. Again, only by understanding these conditions, what causes them and by studying their occurrence in our own breed can we determine to what degree they merit concern. I’ll get into some of those issues in my final article, but for now, let’s look at possible modes of inheritance. To look for possibilities, we could first start by looking at other bobtailed breeds. One breed where there has already been a determination made on the mode of inheritance is that of the Pembroke Welsh Corgi. It has been discovered that the bobtail gene in Pembrokes is actually determined by a simple dominant gene. This discovery was made in a rather interesting way, beginning with the efforts of Dr. Bruce Cattanach, a research geneticist and Boxer breeder residing in Oxfordshire, England. Question: How long ago did you first entertain the development of a bobtail Boxer and what circumstances eventually caused you to go forward with the project?
When the looming possibility of a docking ban in the United Kingdom first presented itself, Dr. Cattanach began to wonder if it might be possible to introduce a natural bobtail trait into his line of Boxers, known by the kennel name of Steynmere. So Dr. Cattanach came up with a plan to breed this trait into his dogs by using a naturally bobtailed Corgi sire and, following a plan outlined by the Kennel club, he documented all his breedings, DNA’d the breeding stock and shared his outcomes in a series of articles (links at the end of this article). Over just a few generations, he was able to reclaim overall Boxer type while retaining the natural bobtail trait. Thanks to the wonders of the internet, I was able to interview Dr. Cattanach and am able to share his experiences here:
Question: How long ago did you first entertain the development of a bobtail Boxer and what circumstances eventually caused you to go forward with the project?
Question: The observations in your premier article of "Genetics Can Be Fun" about how much more acceptable it was to crossbreed a century ago as compared to today bring up what might have potentially been a major roadblock to you. How long did it take to convince the Kennel Club to register the subsequent generations of your Boxers with their partial Pembroke heritage?
Answer: “The KC was not the problem other than one had to make application with justification and rationale for making the cross. The format was already in place and had been for a very long time although seldom used. The problem was the general dog breeder who tends to think in terms of how long it has taken to establish today's breeds and imagines the breed cross will take everything back to beginning again. And then there is also the flawed concept that 'pedigree is perfect'.
The fact that breed type may be regained very quickly, that there are very few genes separating the breeds, and that breed crossing open up all sorts of opportunities for breed improvement, health problems, inbreeding etc, is not generally considered. The KC, with its new genetic moderator, is clearly now thinking more strongly in this direction.”
Answer: “We are about to start the 7th generation and, forgetting about test crosses, there have been one to two litters per generation - in my hands. Elsewhere, as will be mentioned later, I am not sure.”Question: Initially, you decided to maintain breeding rights over any of the bobtail Boxers you used in your breeding program. You've mentioned that you felt responsible to monitor whether or not there were any undesired effects associated with the gene. Thus far, have you gotten any unhealthy pups in any of your litters whose problems could be related to the bobtail condition? Have you continued to maintain breeding rights on your dogs?
Answer: “I kept total control of ALL dogs deriving from the breeding programme until very recently (4 months ago) when demand for these dogs had risen with the recognition that a docking ban will soon be with us. By this time I also felt sufficiently confident to let the gene 'out'.
“I had not found any abnormality associated with the bobtail other than minor tail kinks. These worried me initially, but on investigation, all were shown to be confined to the tail itself, never affecting the spine. This accords with the Norwegian Vet School study on bobtail PWCs. All Norwegian breeding stock are X-rayed for HD and spondylosis and none of the bobtails from the first import onwards have been found to have problems. I still expect the original bobtail Boxer breeder over there to monitor all pups closely.
“I have found one bobtail with a closed anus but also I have had a normal tailed pup with this defect in normal (non-bobtail) but Boxer related breeding. A particular Boxer line seemed to be the problem as I have never seen the defect before or since. A raised incidence of imperforate anus in bobtails therefore seems improbable. I also had a single spina bifida case with this breeding but the affected pup was not a bobtail.”
Question: Records from Pembroke litters in Norway indicate that litter size does not seem to be affected by the presence of bobtail pups, even when both parents are bobtailed. When the gene for the bobtail in Pembrokes was identified and it was further discovered that in a sampling of bobtailed Corgis all of them were heterozygous for the trait, you surmised that the homozygous embryos either did not implant in the uterus or if implanted were shed early in the pregnancy. Technically then, this is a "lethal" gene? Could non-viable or some other term be applicable? Does this "shedding" of homozygous embryos simply then allow for more opportunity for the heterozygous embryos to thrive and survive?
Answer: “The term lethal as applied to the gene mutation responsible simply reflects classic genetic terminology. Non-viable means the same thing. Anything that reduces the numbers of embryos, especially in large litters and especially when this occurs early, is going to favour the well-being and survival of those that remain. The only consequence of practical significance is that the condition will not breed true.”Question: Could the same DNA test that was used to identify the bobtail gene in Pembroke Welsh Corgis be utilized for other breeds as well?
Answer: “The same test could and should be used in other breeds to identify the presence or absence of this particular mutation. There are many tail genes (as evident in the lab mouse) with different modes of inheritances and similar or different types of effects. But if a positive answer is found with the bobtail gene test in another bobtail breed, this would define the same gene as being responsible and would probably define the mode of inheritance as being the same. I should qualify this with the comment that different mutations of the same gene might be found by this means and these would need to be investigated anew. Many different mutations at this one brachyury gene locus (gene symbol T) are known in the mouse. Some have deleterious effects in the heterozygous condition. Hence there is a need for care.”
According to Dr. Cattanach, the DNA test used on the Pembrokes and his line of bobtailed Boxers could be run on Australian Shepherds with natural bobtails to determine whether or not the bobtail gene in our breed is the same one as it is in Pembroke Welsh Corgis. If it indeed is, that provides us with a great deal more information. If not, then we will still have to keep looking and studying. The next article will explain the goals of the study and the methods employed to survey breeders. Later this year, look for the final article in this series (including litter data): Study on the Inheritance of Natural Bobtails in Australian Shepherds
Enormous thanks go to the following individuals for assisting in the completion of this article: renowned British research geneticist Dr. Bruce Cattanach, who so graciously and thoroughly answered all my questions; to CA Sharp, whose knowledge of the breed’s health and genetics make her a true guardian of the Australian Shepherd; and Anne Indergaard of Norway, whose enthusiasm and generosity with her own experiences pointed me in the right direction to some valuable answers.
Web sites and contacts for further information on the genetics and health of animals with bobtails:
|“Breeding Bobtails”, an article by Anne Indergaard, is available from the author at firstname.lastname@example.org.|
|“Breeding Pembrokes for natural bobtails”, an internet discussion by Siri Alnaes: http://corgi.ncn.com/info/bobtails.htm|
|Dr. Bruce Cattanach’s Bobtail Boxers, an article from Boxer Underground: http://www.boxerunderground.com/1998%20issues/oct_bu_98/bobtail.htm|
|“Genetics Can Be Fun”, a series of seven articles by Dr. Bruce Cattanach on the introduction of the bobtail gene into his Boxer line: http://www.steynmere.com/GENETICS.html|
|“Spinal Abbreviation Related Anomalies in Bullbreeds”, regarding screw tails by Carol Hawke at the following Canine Chronicles website: http://www.caninechronicle.com/features/hawke/hawke_903.html|