NAVIGATION


Genetics Can Be Fun - Story of Bobtail Boxers

Part 5, Bruce Cattanach's pen-ultimate report on bob-tailed Boxers

The first four parts of this article were written between 1996 and 1998. They dealt with the production of bob-tail Boxers by means of an initial cross to a bob-tail Pembroke Welsh Corgi followed by repeated backcrossing to Boxer.

Because there will be a substantially new readership since the first report, I briefly review here the progress made, generation by generation, with photos of the key dogs. I then introduce and provide the first answers on health issues associated with the bob-tail gene.

Part 6 will present the final results on health issues and the genetics of the bob-tail condition as relevant for both Boxers and Corgis. The prospects for wider use of the gene in Boxers will then be discussed. I finish with some general conclusions on the study.

REFLECTIONS ON PAST PROGRESS
The study was conceived about 10 years ago. In part it was started as an academic exercise to see how feasible it might be to transfer a gene from one breed to another. But, given the probability that docking would eventually be banned in the UK, as was already happening in other countries, the bob-tail gene was specifically selected because of its potential practical application. The "recipient" breed was my own breed, the Boxer. The bob-tail "donor" was the Pembroke Welsh Corgi.

I have often been asked over the years, "Why use a Corgi, which is such a different breed?"

In truth I had never thought or worried about this. In the series of backcrosses planned, it should not matter what I started with. Unwanted characteristics of whatever nature would all be diluted out, generation by generation. Of more practical significance was the fact that Peggy Gamble of Blands Corgi fame and the late Patsy Hewan (Stormerbanks Corgis) had earlier asked me to investigate the inheritance of the bob-tail condition in the breed. This proved to be that of a single dominant gene, a finding that potentially made transfer into another breed relatively simple.

Beyond this, it was fortuitous that the two main characteristics of the Corgi that I did not want, the longer coat and the short legs, were also inherited as dominants relative to the Boxer very short coat and long legs. This meant that once avoided in any generation, they would be gone forever. Nevertheless, quite apart from these two genes, I was hugely surprised at just how easy it was to get back to Boxer appearance by repeated crossing to Boxer after the initial Corgi cross.

The series of photographs of the key dogs of each generation illustrates the ease of re-establishment. Fig 1 shows the uniform Boxer x Corgi crossbreds. As expected, they all looked alike and in most attributes favoured the Corgi.

In the next generation in which two of these first generation bitches were backcrossed to Boxer, no two dogs were alike. There were short legs - long legs, short coat - long coat, bob-tail - long tail, long foreface - short foreface, shallow head - deep head, scissor bite - undershot bite, and so on. In addition, these dogs showed a range of white markings attributable to different alleles (forms) of the white spotting (s) gene carried by the Boxer and Corgi. Among this second generation was a bitch, Jane, which was Boxer-white and had most Boxer characteristics.

Jane was used for breeding the third generation. She was mated to big typey solid (no white markings) Boxer. All her pups had the expected "show" white markings and all looked Boxer. Only head types detracted a bit, but without prior knowledge no one would have thought "crossbred", let alone "Corgi". The best known of this third generation was George a big handsome very Boxer male, but his two bob-tail sisters, Bobby and Paddy who again looked Boxer were to take the bob-tail into later generations.

Having said this, George produced one litter to a Boxer bitch I had available, and a puppy from this fourth generation litter (now accepted by Kennel Club rules for registration as Boxers) had some success in the show ring. She was even pulled out among the last eight in a general championship show Puppy Sweepstakes. She was not used for breeding as she had a normal, docked tail

George's sisters, Bobby and Paddy, produced the main two lines of fourth bob-tail generation dogs. A Bobby son, Steynmere Hot Shot, could said to be the first bob-tail Boxer. He was KC registered and exhibited. As a big solid red who was quickly bored by the show ring, he was not eye-catching but there was not much wrong with him, and he had a superb Boxer mouth/bite. He was shown primarily to demonstrate the bob-tail condition and illustrate that he was typical Boxer but, nevertheless, he won a few cards in puppy and solid classes at breed open and championship shows.

As a male, Hot Shot could be bred from as an early age and in a cross with one of my Boxer bitches quickly took this Bobby-derived line of bob-tails into the fifth generation. A bob-tail son, Steynmere Total Eclipse was retained for breeding and showing. This chap was more extrovert and more eye-catching than his father, despite again lacking flashy white markings, and he won genuine places in minor puppy classes at three of his five breed open and a championship shows.

He won't be shown much more as, for demonstration purposes, the novelty of bob-tailed Boxers has just about worn off. I think he has just been seen by most breeders as just a decent but ordinary Boxer. A bob-tail Boxer that could win consistently at top show level was needed to regain attention.

Current plans
To try for a top show Boxer, attention has recently focused upon the two fourth generation bob-tail bitches, a Hot Shot sister, Steynmere Hot Stuff, and a Paddy daughter, Steynmere Magic Touch. The latter has turned out quite a nice bitch. Certainly, she impressed Peter Baynes on his recent visit from the USA to judge the Essex and Eastern Boxer Club's millennium show. She came into season a few weeks ago and was mated to one of the country's top producing stud dogs, Ch Faerdorn Fineas Fogg.

Unfortunately, she missed and it will be nearly a year until she comes into season again. Therefore, attention is now directed towards Hot Stuff. She is a sparkling red and white of some show quality. Maybe we will have more luck in breeding with her.

Health issues
From the beginning of this study there have been two health concerns. The first relates to the single dose, heterozygous bob-tail dogs; do they have any risk of associated abnormality? The second concerns the fate of the double dose, homozygous animals; what happens to them?

While it is well-known that some short tail genes in dogs, cats, and laboratory mice etc have associated undesirable consequences, no indication of this has been reported with the bob-tail condition of the Corgi. Thus,

Genetic Expectations
1. Records from breeders collated by Olav Hedne in Norway where bob-tail Corgi breeding is expanding rapidly have not identified any defects among the bob-tail pups, despite full recording of details on live and dead pups, litter size, sex, etc in about 100 litters;

2. there was also no shortage of bob-tail Corgi pups relative to the 50% expectation (Illustration I)

3. a joint Norwegian Kennel Club/veterinary study, using radiography, upon adult bob-tail Corgis taken at random from the population has not found any spinal or other abnormalities.

To this I can add my own observations made on the 5 generations of Boxer crosses,

1. I have produced a total of 31 bob-tail dogs over the 5 generations of crossing. None have had any abnormality that I could detect other than involving the tail;

2. There were 58 pups in these crosses, so the frequency (53%), as with the Corgis, accords with the 50% expectation (Illustration I);

3. an as yet small but ongoing study using radiography has not shown any spinal or other defects in the bob-tail Boxers beyond the tail effect itself.

In summary, therefore, it seems there is nothing to worry about with the bob-tail in terms of undesirable "side effects" with a single dose of the gene in either Corgi or Boxer.

But, what happens in the double dose, homozygous bob-tails? As illustrated in Illustration II, when single-dose, heterozygous bob-tails are crossed together, 25% of the progeny should be the homozygotes, 50% should be heterozygotes and 25% should not carry the gene. No such matings have yet been done in Boxers but in Norway and Sweden many bob-tail x bob-tail matings have been made with Corgis.

Detailed breeding records have been collated by Olave Hedne and these have not even hinted at elevated incidences of abnormal or dying pups. One must therefore conclude that either the homozygotes are born, survive normally, and are not distinguishable from heterozygous bob-tail litter mates, or they are never born and die and then resorbed during the dams' pregnancies.

In the latter situation, an expected consequence would be that the litter size should be reduced by 25%. Yet this is not indicated in Olav Hedne's Corgi data which shows litter size to be no lower than that from bob-tail x normal tail or normal tail x normal tail matings. On the other hand, the observed incidence of bob-tail pups was not as high (66%) as should have been expected (75%, or 3 bob-tail : 1 normal) if the homozygotes are born.

The information from these crosses is therefore contradictory and this has warranted a direct search for homozygotes among the bob-tail progeny of such matings. As far as I have been able to ascertain, there has never been a systematic search for the homozygotes. This hardly surprising because it is a daunting task.

Basically, such a search requires that a number of bob-tail dogs derived from bob-tail x bob-tail matings each be test-mated with normal tailed animals to see if any produce only bob-tail pups. These would be the homozygotes (see Illustration III). The problem is that 12 or more such dogs might need to be tested and each would have to produce 12 or more pups.

This could mean maybe 20 to 30 litters and up to 150 pups to get an answer. Clearly such a huge study is beyond anything I could attempt with my one to two breeding animals per generation. It might even be too much for a group of Corgi people despite the much larger number of bob-tail dogs they possess. But here "Lady Luck" in the form of the new scientific advances has stepped in.

Part 6, Bruce Cattanach's final report on bob-tailed Boxers

In last week's report I reviewed the progress, generation by generation, of transferring the bob-tail gene from a Pembroke Welsh Corgi into the Boxer and presented evidence that there are no health risks associated with the gene when in the single dose. But, for the double-dose, homozygous bob-tail dogs, the evidence was contradictory. Norwegian Corgi data indicated a shortage of bob-tail pups (66%) relative to the 75% expected from bob-tail x bob-tail matings, suggesting that the homozygotes are lost before birth.

But there was no evidence of a reduced litter size. To search for the homozygous bob-tail would require a massive breeding programme. But, scientific advances derived from molecular genetic studies on the bob-tail Boxers and Corgis have more quickly provided the answer.

The scientific breakthrough
With the development of the new molecular expertise in the world of genetics and the increasing interests in studying species other than mouse and man, my crossbreeding studies in the dog had begun to attract attention outside the world of dogs. In this connection I was delighted when a human genetics group whose main interest lies in the genetics of facial features contacted me.

They were looking for an animal model to test out candidate genes for human facial characteristics they had isolated. My cross between the Corgi and Boxer with their different head types seemed to provide the ideal test material. And the whole concept became a practical proposition when they learned that I had already collected blood samples over the generations of crosses and that Jeff Sampson at The Kennel Club and Matthew Binns at The Animal Health Trust had made the DNA that would be needed. All was set to go when there was a further stroke of luck.

The human genetics group had also been working upon a DNA sequence that is homologous (corresponds) with that of a mouse gene that causes a dominantly-inherited short tail. As a side project, therefore, the group asked if would I be interested in their checking to see if this gene was responsible for the Corgi bob-tail? Would I indeed? There are many short-tail genes in the mouse, so the chances that the group might be working upon the same gene was small. But, nevertheless, it seemed worth testing, and the study started. Amazingly, it was the same gene.

To show this the group sequenced (read the genetic code) all the way through the bob-tail gene of the Corgi that was used in original Boxer cross and they identified a single change in the DNA. Was this responsible for the bob-tail effect? To establish this it was necessary to show that all the bob-tail dogs in the Boxer crosses had this variant DNA sequence and all the normal tailed dogs did not. And this was indeed found (with one exception which I will deal with later). The bob-tail mutation had therefore been identified.

The findings are of considerable scientific interest, so much so that a paper has already been submitted to a leading genetics journal for publication. But, for me, the results were of more immediate practical use. The identification of the gene meant that it would now be possible to distinguish dogs having one and two doses of the gene - just by analysis of blood samples. None of the laborious and expensive test-mating would be needed.

A call went out to the Corgi people in Norway who were intercrossing bob-tail dogs. Blood samples from 13 bob-tails produced from such matings were obtained and I was able to raise one more in this country. The DNA was prepared from each blood sample and analyzed independently by the human genetics group here and by the Norwegian Kennel Club geneticist, Frode Lingaas.

All 14 bob-tailed dogs derived from the intercrosses were found to carry only a single dose of the bob-tail gene. The failure to find any homozygotes among 14 bob-tails tested means that the homozygous, double-dose class must be missing. But this class must be generated at conception (Illustration II). So where have they gone?

It can only be concluded that such pups die. But when? From Olav Hedne's ample Corgi breeding records it is clear that there is no increased incidence of puppy deaths in bob-tail x bob-tail litters after birth. The loss of the homozygotes must therefore occur before birth.

Prenatal loss of the homozygous bob-tail pups means that they die either early, during embryonic development, or later, in foetal stages. Two reasons suggest that the loss occurs early. First, no aborted or dead pups have been detected at birth. Second, based on substantial Norwegian and Swedish records, the litter size of bob-tail x bob-tail litters is not reduced as it would if foetuses died and were being resorbed. With early loss, however, an explanation for the seemingly contradictory evidence can be offered.

In animals that have a number of offspring at once (in litters) there is a natural wastage as has been well-documented with laboratory mice. Not every fertilised egg implants in the uterus. Not every implanted embryo survives to term. And, this is especially evident with larger litters when there is competition for uterine space and nutrients. Embryonic loss is common around the time of implantation in the mouse. The hypothesis for the bob-tails is therefore simply that homozygous bob-tail loss replaces natural loss. Their loss in effect enhances the chances of other embryos surviving.

Ethical considerations
Whatever the correct interpretation of the discordant evidence, the molecular data establish that the homozygous Corgi bob-tail is a lethal condition. The term, lethal, has an ominous ring to it. It suggests something totally undesirable. Yet, having pondered the issue at length I have to conclude that while the evidence of lethality is disappointing, it is not an ethical problem.

Without any detectable ill-effects, the only undesirable feature of the bob-tail condition is that it will not breed true. There will always be a 25% expectation of long tailed pups appearing (see Illustration II). That we now know why this occurs simply means that, in a sense, we now know too much.

So! If there are no ill effects, if litter sizes are not reduced, if the only unwanted feature is the persistent appearance of some long tailed pups in litters, is this acceptable in the event of a docking ban? I suggest that it is now up to individuals to decide on this, and as I am now content that there is nothing nasty about the gene, I see no ethical reason for continuing to keep total control over these bob-tail Boxers. The situation is no different from that for all other breeds having this bob-tail gene.

Release of bob-tail Boxers
There has been relatively little enthusiasm for the bob-tails among UK Boxer breeders. But there has been considerable interest abroad, in particular, from Norway where a docking ban has been in place for some 10 years. Norwegian interest has attractions for me as the Norwegian Kennel Club already has an interest in the gene.

Moreover, together with the Boxer club, they have a rigorous health policy in which all breeding stock has to pass heart, HD, and spondylosis tests and there appears to be general interest in record keeping. Sending bob-tail Boxer stock to Norway, specifically to such health enthusiasts would take a lot of the weight of continued monitoring from me and could be done as part of normal breeding practice.

Accordingly, Steynmere Hot Shot has gone to Norway. His heart murmur-free status attained in the UK has been confirmed, and he has also been found spondylosis and HD free. His new owners (although he is actually co-owned with me) are delighted with him as a Boxer and even plan to show him. In Norway he will not be the only solid dog in the show ring, and he will be among other big Continental type dogs.

He has already mated his first bitch and there are plans to mate him to a number of others. And all the progeny will be rigorously monitored. Beyond this, the dog has gone to an enviable home as he will live as a single dog in a long-time Boxer-loving family with runs in the forest each day.

There have been enquiries for bob-tail Boxers from a number of European countries and even from the States. But everyone wants bitches and I don't exactly have many to spare. At present, I only have the two bob-tail bitches (on terms) and one other puppy, plus the Hot Shot son, Total Eclipse, who could no doubt be of use were there interest. From this I think it should be clear that I cannot do much more alone.

General conclusions
This project has effectively demonstrated that a gene can be transferred from one breed to another with relative ease. Breed type can be quickly regained by backcrossing and, after five or more generations, the chances of any "foreign" genes remaining to reverse this are very small.

The gene used had a dominant inheritance which made the transfer very simple. With a slightly different strategy, a recessive gene could be so transferred.

The Corgi bob-tail gene was selected for this project in view of its possible use in the event of a docking ban. It effectively gives a docked tail image but has the disadvantage that it will not breed true. There may therefore be other, better genes such as the short, kinked tail of the Boston Terrier or even the seemingly natural shortish tails of certain other terrier breeds. But the inheritances of these are not known as far as I am aware.

The success of the project highlights opportunity for all breeds - whenever a gene is needed for whatever reasons. Breed crosses can have an important use, particularly with health issues in numerically small breeds as The Kennel Club has already recognised. Perhaps acceptance of cross-breeding for specific purposes may be the greatest legacy of this bob-tail project.

Postscript
I mentioned earlier that one presumed bob-tail dog in the Boxer backcrosses was found not to have the bob-tail mutation. On closer inspection it was found to have a twisted, bony screw tail. which did not have the typical fatty distal pad with the terminal filament of the bob-tail. Bizarrely, it seemed to be one of the tail defects that occurs not uncommonly in various breeds, and seemingly quite commonly in Boxers. As many people know I am currently showing a Boxer with such a screw tail. But it has seemed quite ridiculous to find a screw tail in this bob-tail study.

In past years I have test-mated some of these screw tailed dogs but have not found the condition to be inherited. I therefore would not expect this screw tailed bitch to produce more like herself. But, partly to prove the point, I am test-mating her. Although there is another reason!

The screw tailed bitch is from the fourth generation of crossing and looks typical Boxer. To test if she would transmit the tail effect to her progeny, she was mated a few days ago to a normal tailed dog, But to "kill two birds with one stone", I used a Hot Shot brother so doubling up on Corgi. The reason for this choice was to verify that no short legged, longer coated little Corgi-type dogs will reappear, as the critics of the cross-breeding would predict. We shall see.

I hope this and preceding articles illustrate something of my interests in genetics. Recognising anomalous situations, investigating them, and finding the answers is, for me, the type of genetics I enjoy and which I have been privileged to be able to pursue throughout my working life. It is so very different from the horrors of developing and operating control schemes for genetic disease.

Have I convinced anyone that "GENETICS CAN BE FUN"?

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