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By: George A. Padgett, DVM
Professor in the Department of Pathology, College of Veterinary Medicine at Michigan State University
The first and major hindrance to recognizing
the significance and cost of genetic disease is that most breeders believe
that the MAJORITY OF DOGS ARE GENETICALLY NORMAL. This is not the
case at all. Aside from what is likely to be the case, if you believe
most dogs are genetically normal and you find out your dog carries a defect,
whether it's cataracts or something else, you do not want to talk about
it because you believe your dog is different (less worthwhile) than MOST
This belief causes a person to be secretive
about a trait, to deny that it occurs, and, as a result, to fail to
It is difficult to convince breeders that ALL dogs carry defective genes because people tend to hide problems and thus they are not an obvious part of the productivity of a dog or a kennel. However, the elite of the breed, the superior dogs, those that contribute a disproportionately high number of genes to the gene pool of the breed, allow us to get a better look at the problem for two major reasons.
• The first is that a good stud is used on bitches outside the control of the owner of the stud and thus the offspring of the stud are observed by multiple people and with multiple people it's hard to keep a secret. As a result, GOSSIP occurs. It may be true (also may not) but it's treated as gossip and sort of whispered rather than being openly discussed. Alternatively, a stud of lesser quality and not as well used, producing, say, two litters, may well have expressed the identical gene but the gossip is controlled (only two breeders are involved).
• The second reason relates directly to the first. For a genetic disease to exist in a breed, there must be affected dogs, carrier dogs (those having one gene for the trait), and dogs normal for both genes existing within the populations. Obviously, a dog bred more widely has a better chance to contact a carrier bitch and thus give the trait a better chance to express itself than a dog that produces one or two litters, even though both dogs are themselves carriers [controlled test matings may be the only way to establish who's who].
As a result of these two major features of genetic diseases and dog breeders (odds of producing a defect and gossip), you cannot name a single major dog in my breed that has produced 200 puppies or better (40 litters, 5 per litter) that has not produced some defect (try it, see if you can think of one). Further, once you know the dog has produced a recessive defect, then you know that each of his puppies has a 50:50 chance of being a carrier for that defect whether the puppy was born before the stud produced the defect or after he produced it.
What breeders most often forget, however, is
that the reason you know a superior dog has a defect is that the dog is
in fact superior. He is used more often than dogs of lesser status because
he produces winning offspring. He adds quality to the breed or he would
not have been allowed to produce so many puppies (remember, this is controlled
by the owners of the bitches, not the owner of the stud). WE now have 200
puppies on the ground, many of which are already champions (or you wouldn't
have 200 puppies on the ground!), half of which are carriers. The owners
of these dogs have already made a large investment in them and now they
do not want to talk about any defects involving their dogs. What I call
"THE CODE OF SILENCE" is imposed; it is unethical to talk about defects,
owners that talk about defects are though of as abhorrent. Breeders that
admit their dogs have or carry a defect are hounded by others no matter
what quality the dog nor how healthy the dog. The stage is set for what
breeders do best to one another: THEY LIE TO EACH OTHER or they evade or
they do not involve themselves in "useless" discussions or they fib or
they do anything they can to avoid the fact that THEIR dog carries a gene
for a given defect or may in fact have the defect (if it cannot be observed
without special techniques).
Dog breeders in general ... cause defective genes to spread within a breed by failing to approach genetic defects in an open manner. They control the matings of their dogs, but somehow they end up expecting "nature" to correct defects in the same manner natural selection works in a wild population. If "nature" bred their dogs there might be some basis for the belief that a disease such as cataracts might be corrected over a period of one or two hundred years by natural selection. The fact that none of the breeders (having the belief that natural selection is protecting them) would be alive when it happened doesn't seem to faze them.
Dog breeders in general need to face genetic
defects as a realistic part of the problems encountered in the process
of producing good sound animals. We need to quit whispering about defects
and gossiping about defects and instead set up a sound program that allows
the standard selection procedures to go on so that we breed good dogs and
avoid major defects.
Solving the Problems and the Painful Truths
There is no easy answer to get rid of defects in dogs. Remember
most dogs carry 14 disease/defective traits that may come up in your breeding
program at some point.
Hip Dysplasia is one of them. Some experts say its genetic while others say it’s due to early injury and still others theorize that it’s a combination of nutrition and environmental factors.
The general consensus on Patella Luxation and Legge Perthes has been assumed that it is recessive in nature and that in order to produce a pup with the problem both parents must be carrying it.
Demodectic Mange is a great one under controversy. Since all dogs have the mites on them from birth it can be rather hard to determine if the pup breaks out because of stressful conditions or if there immune system has not fully matured yet or if its strictly genetic.
Under or Over shot jaws can be caused by genetics or by breeding two dogs with dissimilar head shapes. Meaning one dog has a long muzzle and the other parent has a short muzzle. The upper and lower jaws grow at different rates so that if a puppy has a good bite when very young and suddenly goes over or under there is a chance that the bite will self correct once the jaws catch up with each other. That is not always the case though.
The list goes on and on with defects but two healthy dogs that have been bred several times without occurrence of problems can suddenly produce a defect that shows up.
If you breed a male and a female and come up with defects then you can not always be sure that both of the parents are carriers when they do not express the defect themselves because of the lack of information on genetic inheritance modes. Generally speaking though, if both parents are carrying a bad recessive trait, a quarter of there offspring will show the defect, half will be carriers and a quarter will be free of the problem. It is now impossible to say which offspring are carriers and which are free of the defect. The affected ones are obvious.
1. If you are not a serious breeder and do not have enough dogs or different lines to work with in order to breed out an undesirable trait that has showed up suddenly in your lines then spay/neuter the dogs that are in question and all offspring produced if they had been being considered for breeding. This means that if you are someone who purchases pups from different sources because they are nice pups and have not bred those lines to tell what defects they carry or do not know about the complete history of the dogs you are just breeding unknown factors into the offspring each time you breed. The truth of the matter is that you are not a breeder, your just breed dogs.
2. If you are a dog owner with a couple of dogs and like to have a litter once in a while, be sure that you check up on the pups that you have sold to be sure that they do not have any problems. If even one pup comes up in any of the litters do not breed those dogs again.
3. For those who are a true breeder with substantial breeding stock and are willing to work in the “breeding out” of a trait over time you stand a good chance of producing excellent pups to move into the future with. It is time consuming, trying and an expensive venture. You would need to have test bred your dogs to find out exactly what they do and do not contain in the way of good or bad genetic traits, which is a 5-7 year long process at minimum. Of the test bred dogs, do not sell those pups that are in question or might carry a negative recessive gene to other breeders unless you are fully prepared to disclose this information to them. The offspring will show no signs of illness but when bred to another carried the negative trait will come back to the fore front. There is no way to predict when it will show up unless you can trace the lines back to a common dog in the ancestry that is a “known carrier”. And this means not just a dog that appears in the pedigree on both sides but a dog that is common as a “known carrier”. Also require a spay/neuter contract to all buyers of those pups if they are going into private homes.
advice from experts and some options:
Limit reproduction of known carriers for the long-term genetic health of the population but then a high number of individuals must be removed from reproduction. Some of these carriers are bound to be otherwise exceptional, and these are the animals for which the choices become very difficult.
Another method is to neuter the affected individuals as they become known, the parents of the defective individual, and all of their previous offspring. This is the most radical selection against a defect, and it effectively removes carriers from the population as they are detected as well as some noncarriers. So while the "neuter all carriers" approach will work to dramatically reduce the number of carriers in a population, it rarely completely eliminates all carriers since some slip through the cracks of the system.
A less drastic than “neutering all carriers” plan is to neuter the sire because he can spread the gene more widely than can the dam, which produces fewer offspring. Still half of the offspring of the carrier dam will be carriers. One approach is to neuter all of her sons but allow her daughters to reproduce. About half of these will be carriers. If these are in turn used for reproduction, the carrier rate goes down to about one-fourth, although which specific fourth is uncertain without a breeding test.
If excellent males are generated, an alternative to the above scheme would be to test-mate them to known carrier females to determine which of the males do not carry the defective gene. Those documented as free of the gene can then be used widely and safely for breeding of animals free of the specific defect. In this way, the positive traits of the line can be continued while leaving behind the defect. The process is long and involved but well worth the effort in some circumstances.
So remember no matter how perfect a dogs conformation is or how beautiful he looks or how many shows or titles he has won, beware of what may be hidden deep in the lines in the way of recessives. You will NEVER know that the recessive is there until you happen on another dog which carries that same recessive and viola, you have a big problem. Unfortunately this can not be foreseen the vast majority of the time and pretty much every time you breed a dog it is a test breeding unless you have had those lines for many years and test bred each of the dog with several mates. For each time you outcross a dog into new lines it is like starting all over again. What lurks behind them can not be predicted. You may cross dogs without problems to several mates for several generations and it’s that one time that the wrong two dogs come together and the problem rises to the surface so fast that you hardly can believe that it’s happening.
It is so commonly said that “I got a bad dog from a breeder”, that breeder may not have had any idea of what recessive the dog was holding. When that unknown recessive was bred to your own dog and you got a bum litter, well then you at least found out that not only did the breeder you bought the dog from carry an undesirable trait but yours did too. Now it’s back to square zero again. It’s also commonly said, “How could the breeder not have known?” That’s easy enough, the wrong genes in there particular program never came together.
In the Rat Terrier breed specifically the problems that seem to be coming up are due to the fact that it is a fairly recent breed that has come into popularity. More dogs are being sold and or traded across the USA. They are a mixture of many different breeds from long ago, some containing more blood from certain breeds then from others depending on the geographical location they came from. When blood from one of the original breeds that was crossed in comes together and that particular breed had an abundance of problems, surely those problems would show up once again. As the breed becomes more and more pure in its own strain as a Rat Terrier the genes start doubling up for good and for bad. In the early stages of the Rat, there were many outcrosses made to several different breeds. This is called Hybrid Vigor. The dogs were very hardy because they are carrying many genes that are different from each other. Once those genes start doubling up, for good or bad you start to see the problems that were always there in the first place.
The bottom line is that in every breed there are problems and those problems are going to show up from time to time. The only way to start producing dogs free of defects is to watch our lines closely for problems that crop up and correct them immediately. That means to use one of the techniques as described above. There is no sense in blaming owners, breeders but only ourselves. We all know when a problem arises and common sense should take care of the spread of the problems. Breeders should try to find any defects and halt them. Not blame other breeders for bad dogs which they may not have known about in the first place., but talk about what might have gone wrong somewhere in the lines and don’t repeat the mistake. Owners should at least notify a breeder if a pup they bought came up with a problem somewhere down the line. If a breeder is unaware of any pups produced with a problem there is nothing they can do about it. We all try and do our best, lets continue to do that and keep the Rat Terrier breed going as defect and disease free as possible.