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 Boxers.
Because there will be a
substantially new BU 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 gene(s) carried by the Boxer and Corgi.
Among this second generation was a bitch, Jane (Fig 2), which was Boxer-white and had most
Boxer characteristics.
Jane was used for breeding the
third generation. She was mated to a 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
(Fig 3), a big handsome very
Boxer male, but his two bob-tail sisters, Bobby (Fig 4) and Paddy (Fig 5), 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 (Fig 6) 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 (Figs 4 & 5), produced the main two lines of fourth generation bob-tail dogs. A
Bobby son, Steynmere Hot Shot (Fig 7), 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.
Steynmere Hot Shot
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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 (Fig 8) 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 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 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.
Steynmere Total Eclipse
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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 (Fig 9), and a Paddy daughter, Steynmere Magic Touch (Fig
10). 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 (Fig
9). Maybe we will have more luck in breeding with her.
Steynmere Hot Stuff
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Steynmere Magic Touch
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| 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,
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;
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 five generations of Boxer crosses:
1. I have produced a total of
31 bob-tail dogs over the 5 generations of crossing. None has 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.
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? 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 are 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 is 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. 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.
Total Eclipse
|
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.
Magic Touch
|
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.
Magic Touch
|
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, 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. 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 (Fig 7 of Part 5) 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 (Fig
8 of Part 5), 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 (Fig 11). 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 (Fig
12), 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.
Fig 11
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Fig 12
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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"? |
