DISCUSSION ON HIP DYSPLASIA

The following educational articles are from The American Border Collie Website! To be considered a genetic disease, a health problem needs to have been demonstrated to be inheritable, that is, passed on through one or both parents. Some diseases have high heritability, which means if the genes are present, the individual will have the disease, and some diseases have low heritability, meaning both genetic and environmental factors are involved in whether the disease occurs. It is generally easier to control diseases with high heritability because all individuals with the genetic makeup for the disease can usually be identified. The term heritable disease should be distinguished from the term congenital disease, or problems that are present from birth, which may or may not be heritable.

 Border Collies are considered to be a generally healthy breed. However, as in all animals, there are some potential health problems. This information is presented to help both breeders and buyers to become more aware of some of the health and genetic issues in the breed at this time.

The primary genetic diseases currently thought to be a problem in the breed are as follows: Hip Dysplasia (HD) HD is by far the most prevalent known genetic disease that affects Border Collies. Factors that contribute to the development of HD ultimately cause the hip joint to be damaged. Joint damage called osteoarthritis, also known as degenerative joint disease (DJD) is manifested by cartilage and bone breakdown and irregular bony remodeling in response to stresses and inflammatory processes in the joint. DJD is, in effect, the identifiable result of factors that cause HD.

The standard for diagnosing HD at this time is still the front extended-leg view of the hips on x-ray such as that evaluated by The Orthopedic Foundation for Animals (OFA). OFA reports a 12.6% affected rate for Border Collies evaluated from 1974-2000. This HD incidence ranks them somewhere in the middle of the dog breeds. Pre-submission screening and selection for probable favorable OFA results by owners and their veterinarians very likely skews this percentage significantly to the low side. Therefore, the true incidence of HD is probably much higher, possibly as high as double the OFA figure. If true, this would mean, on average, one out of every four Border Collies has HD. 

Despite what some may claim, data from numerous scientific studies provide overwhelming evidence that HD is an inherited disease. It is thought to be caused by at least three and possibly as many as six primary genes. The number of genes involved, combined with the high incidence, means it's probable that most Border Collies are at least carriers of one or more of the genes that can contribute to the development of HD, even if they don't have the disease themselves. To confuse matters more, the expression of the disease is affected by environmental conditions such as the type and amount of food a dog gets at critical growth stages, as well as the type and amount of exercise and activity it gets. It must be remembered, however, that these environmental factors do not cause HD. They merely affect whether the HD genes present in that individual will be expressed to the fullest. Even if the expression of HD in a certain individual is suppressed by careful control of environmental factors, you have not changed the dog's genetic makeup. That dog will still pass on the genetic tendency for HD just as if it actually had the disease. Conversely, if a dog does not have the genes for HD, it won't develop the disease no matter how it's raised.

The possible incidence of one in four dogs may seem falsely high if the presence of HD is defined by dogs showing significant lameness.  The clinical symptoms of HD do not always correlate well with the severity of the disease as judged by radiological findings. Border Collies with HD that are fortunate enough to show few if any symptoms may have progeny that are not so fortunate.  The exact complex combination of genetic and environmental factors that contributed to an individual's lack of symptoms will not occur in its pups.  Therefore, it is important to remember that a high tolerance of an individual for the effects of HD does not mean that individual is suitable as a breeding prospect.

 The best way, at this time, to avoid producing puppies with a predisposition to develop HD is to test both parents and be aware of the hip status of other related dogs such as the parents' other progeny, the parents' parents, and the littermates and half siblings of the parents. The more tested, unaffected dogs there are in the pedigrees, the better the chances of producing unaffected pups. Unfortunately, even following the most stringent guidelines, puppies may still be produced that will develop HD. This does not mean there's no point in testing parents before breeding them. This line of false reasoning is akin to arguing that, because working parents will occasionally produce pups that won't work, there's no point in testing the working ability of breeding stock.

Selection for good hips will increase your chances of producing pups with good hips, but it's unrealistic to expect that puppies with HD will never be produced from tested, unaffected parents. Likewise, it is unrealistic to expect every dog who has ever produced a pup with HD to be banned from breeding. Since it's likely that most non HD-affected Border Collies are carriers of one or more of the genes for HD, most dogs will produce at least one pup with HD if bred enough times. Sooner or later, a cross with another carrier will produce the wrong combination of the HD genes and an affected pup will result. Given the incidence and complexities involved with HD in our breed, the recommendations at this time are to breed only hip tested, unaffected parents. Also, try to plan crosses having as many tested, unaffected dogs in the pedigrees of both parents as possible. If an affected puppy is produced from a cross of two unaffected parents, at the very least, don't repeat that particular cross because that affected puppy has proven that the two parents can together provide the right combinations of genes to create more puppies with HD.

The ABCA Health and Genetics Committee is investigating a promising new technique that measures several factors involved in the development of HD. This procedure involves taking hip x-rays on a sedated dog while the dog is in a kneeling position. This angle is favorable for identifying strengths and weaknesses in the hip joint in a more natural, weight-bearing position. This type of measurement is called a Dorsolateral Subluxation (DLS) measurement. ABCA is planning a study to evaluate this technique in 8-12 month old Border Collies.

THE FOLLOWING LINKS & STATS ARE FROM THE OFA WEBSITE: **NOTE: BORDER COLLIES RANKING OR THAT THEY'RE NOT LISTED!

http://www.offa.org/hipstatbreed.html Breed Rank Number of Evaluations Percent Excellent Percent Dysplastic

BORDER COLLIE 76 5726 11.4 11.3 http://www.offa.org/elbowinfo.html

BORDER COLLIE 60 597 98.8 0.8 0.5 0.2 0.2

http://www.offa.org/patluxstatbreed.html

http://www.offa.org/cardiacstatbreed.html

http://www.offa.org/thystatbreed.html

http://www.offa.org/dnainfo.html

http://www.offa.org/deafinfo.html p> http://www.offa.org/sainfo.html

CERF INFORMATION: http://www.offa.org/cerfdata.html THEIR WEBSITE: www.vmdb.org/cerf.html

NOTE THIS LINK: http://www.bordercollie.org/core.html

NOTE THIS LINK: http://www.ansci.cornell.edu/cat/cg01/lk_breeds.html KEEP IN MIND, THAT SO FAR THEY'RE SAYING THAT HIP DSYPLASIA IS POLYGENETIC MEANING MANY GENES CONTRIBUTE TO IT'S EXPRESSIONS:

GENES AND HIPS   USBCC Newsletter, Summer 1994

A number of members have asked about the genetics of Hip Dysplasia. Should I refuse to breed my male dog to any bitch with less than Good or Excellent hips? How many dysplastic pups should I expect if one parent has bad hips? Should I breed a dog with severely dysplastic siblings? Does HD result from inbreeding? Unfortunately, the answer to all of these questions is "I don't know."

 As in most of genetics, breeding good hips is largely a matter of chance, or probability. Unlike more simple genetic traits, however, good (or bad) hips don't result from a single pair of genes. With a single pair, like the "red" genes I described in the last issue, the probability is easy to measure. We know exactly how many red pups, statistically, to expect from any combination. Hips, however, are affected by a large number of genes: some may be recessive like the b that causes red color; some may be dominant like the B that causes black. The problem is that we don't know how to identify any of them, and we have no idea how many there are. If we had hip measurements on all the members of hundreds of litters and their parents and offspring, we could make a start. We aren't even close.

The genetic situation goes something like this: there is some indication that HD might be caused by a combination of three different recessive pairs, call them aa, bb, and cc. Remember that every dog carries two copies of each gene and passes only one on to each pup. A dog that has the combination AaBbCc may pass on ABC, ABc, Abc AbC, aBC, aBc, or abc to any one pup. To form a single pair, again as in the case of the red dogs, the deleterious gene must be inherited from both parents. This would mean that mother and father would each carry at least one recessive copy of each of the three genes, and pass one of each to a particular puppy--that pup would then be dysplastic.

Other pups in the same litter might receive only one of each, or one a and one b and no c at all, or any of many, many combinations. The abc pup could pass all three to the next generation and produce dysplastic pups in turn if he is bred to another dog carrying all three recessives. The ab pup could never produce dysplastic pups because he doesn't have a copy of c. (He can only get one copy from each parent) All these genetic combinations, and others, could occur in the same litter. It is also possible, though, that the genes which in combination produce hip dysplasia are dominant--A, B, and C. In this case, only one copy of each is necessary, and each one would only have to come from one parent.

A dysplastic dog, AaBbCc, could easily pass all three to one or more puppies in a litter, with no genetic help from the other parent. We all know that two perfectly "normal" dogs can produce dysplastic pups. How is this possible? If the genes are recessive, this would be the common genetic condition, exactly as two black dogs can produce a red puppy. If they are dominant, one parent may carry, say, A and B; the other may carry only C. Neither parent has the combination that creates dysplasia. Together, they may pass on to one or more puppies the three dominant genes that make bad hips.

The probability of creating recessive combinations (aabbcc) is greater if there is a lot of inbreeding. Genes follow family lines and the same ones are simply more likely to be found in other members of the same lines. The chance of combining several independent genes (ABC), however, is greater in cases of outbreeding. No matter how many times you introduce into a pedigree a family line carrying A and B, dysplasia will not occur unless you outcross to a family carrying C.

Since we have no way of recognizing any of these until they come together, we can't know what lines to avoid crossing--until it happens. Certainly, if a particular pair of dogs produces a dysplastic puppy, we know the possibility is there; the combination shouldn't be repeated. Unfortunately, of course, we don't know until the puppy has grown up. In either case--and I stress that both are hypothetical and that the truth is probably more complicated than either--the severely dysplastic dog should not be bred.

I hear breeders say that a really good working dog should be used anyway, and the problem sorted out in later generations. It is exactly the really good dog with really bad hips that is the greatest danger. If he produces a lot of top quality trial dogs and enters the pedigrees and the major bloodlines of the breed, his dysplastic genes will be spread throughout the breed. Sooner or later, his descendants will begin to be bred back to each other. If the genes are recessive, we know what multiple linebreeding can do--that's why Wiston Cap has given us an increase in red dogs. If they are dominant, you have created a line in which all three dominant genes are rattling around. From time to time a descendant of our AaBbCc dysplastic dog carrying only A and C will be bred to a descendant carrying B or maybe A and B. This pair is going to produce some pups with bad hips. The more crosses there are in your pedigree back to this ABC dog, the higher the probability that the three genes will come together. Actually, for all the excuses we use for the high incidence of dysplasia (it's the pet/obedience owners; we're feeding them too much, etc) the usual cause for a high frequency of a detrimental gene in a breed is that it occurred in an extremely popular sire whose genes are now everywhere in the breed.