PERSPECTIVES ON HIP DISPLASIA
by Charlie MacInnes, Finnshavn, Canada
The conventional wisdom says that hip dysplasia is not a problem in the Cardigan Welsh corgi as a breed. That does not mean that the breed is completely free of dysplasia. Crippling dysplasia is, however, rare enough that some breeders do not habitually X-ray their breeding stock. It is uncommon to see a Cardigan with a crippled or tender rear, or suffering from the early onset of arthritis of the hips.
I believe there are at least 5 groups of factors contributing to hip dysplasia, and these are not mutually exclusive - as will become evident. That generates the tough analysis problem that the different factors may contribute different amounts, and may interact, so that it is very hard, if not impossible, to sort out the effects of each factor separately. Relative contributions may vary from one breed to another, and among individuals within a breed. The result is that it is difficult to see how best to reduce the probability that future puppies will grow up dysplastic.
Hip dysplasia means that the hip joint is unstable or less than optimally functional. One may argue that the hip joints are the two most important joints of the dog's skeleton. Virtually all the power which drives the dog forward is generated by the muscles of the hind limbs, and that energy is transmitted to the rest of the dog through the hip joints - hence their extreme importance. There is more to the joint than just the shape of the bone. The joint is also held together by ligaments, and to some extent musculature can also contribute to further soundness of the joint. One vet I know who also breeds and shows (Gordon Setters) told me that she believes that loose ligaments contribute as much to dysplasia as the morphology of the hip sockets. Since OFA looks mostly at bone morphology, but PennHip also measures the tightness or laxity of the ligaments, score one plus for PennHip. PennHip also gets another plus in my book from a policy. When you sign the form to have a dog subject to the PennHip procedure, you agree that, no matter what the X-rays look like, they will be submitted to PennHip, and will get into the database. I have several times stood with my partner and her vet and looked at a fresh X-ray, and we decided - no, there is no point submitting this to OFA, it won't pass. While the PennHip system is better in that regard, it is not perfect. Only when breeders and owners submit results from every puppy in every litter will we get true statistics. The definitive studies on dysplasia, mostly in German shepherds or Labradors resulted from X-raying of all members of a pedigree group. A third plus for PennHip is that it can be done at much younger age - and still produce valid results. With both OFA and PennHip, it is a plus if you can find a vet who has experience with dwarf-legged breeds, as the heavy muscling combined with short legs create unusual problems.
So what are the 5 factors?
was heartened to learn - at the seminar arranged by the committee who staged the CWCCA
supported entry in Franklin, Tenn (Nashvillle) in March 2004 - that the major dog food
manufacturers have responded to this nutrition problem, and that today's large breed puppy
foods do not have the very high protein etc. levels. They are in fact very similar
in major nutrients to adult foods, but differ a bit in calcium and vitamins. It is
also worthy of note that companies produce at least two puppy rations, recognizing that
large breeds have different requirements than small breeds. Question - should
Cardigan puppies be considered large breed or small breed? I vote for large breed.
Cardigan I heard of recently (sire OFA excellent, dam OFA good) had to retire from
competitive flyball and agility at six when his hips degenerated and became painful.
But then, in one two-day tournament he made 40 runs, 4 jumps per run. Is that
too much? We really do not understand how much hard exercise Cardigans got when they
worked on Welsh hills farms in 1800!! What was our dog designed to do?
There have been a lot of experiments in population genetics to see how much progress you can make. The classic result is that you make rapid progress at first, then improvement flattens off for many reasons. In Drosophila (fruit fly), the early experiments worked on the number of bristles on the thorax - since no one knew the function of those bristles, they were thought to be neutral in terms of natural selection. But, as the bristle number became higher, other problems arose, the most serious of which was disastrously low fecundity. Really hairy fruit flies just didn't produce young. A member of my PhD committee suggested that one reason for this was that, when you select severely, you probably throw away whole chromosomes just because they did not have the best bristle genes. In throwing away whole chromosomes, you lose a lot of "good" genes, having nothing to do with bristle number, just because they happened to be on the same chromosome as the poorer bristle number genes. So, for those who do not want to see us lose genes for Cardigan type just to help get rid of dysplasia, they are backed up, in the broad sense, by a huge amount of research results on a variety of species.
There is a theoretical possibility which I shall mention, but not discuss. We could have two kennels which put a high priority on selecting for good hips, while line breeding within their own programs. Both might achieve better hips, yet crosses between the two lines could be disastrous. Using the example above, kennel A might, by pure chance, have worked on increasing the frequencies of A, B, and C, while kennel B might have concentrated on D, E, and F. I actually heard of a similar case involving temperament in Golden retrievers.
There is a whole different way to look at the problem of dysplasia being multifactorial. Genes do not work in isolation. It may take several genes to make a hip socket, yet it is unlikely that any of them work just on the hip socket. Some genes regulate the amount of action of other genes. Thus, growth is turned on or off, and its rate is speeded or slowed, by genes acting on other genes. One consequence of this knowledge is that there are probably not genes for good or bad hips, in isolation. So getting growth speeded up may be good in one part of the body, but bad somewhere else, for example, in the hips. That means that in selecting for some good characteristics, we may inadvertently end up with poorer hips, because we certainly do not know all the linkages between genes.
has now been 50 years since the first experiments began on selecting breeding stock to
have better hips. The experimenters have had
little trouble deriving breeding lines that are seriously dysplastic. However, the desirable result, a pedigree which
never produces dysplastic hips is still a holy grail for breeders. My own summary is that genetics does contribute to
hip dysplasia, but, perhaps by chance, not a great deal among Cardigans of today. We
need to be vigilant. However, I have been around a lot of Cardigan puppies, and I
have never seen one having the sorts of problems that are all too common in labradors and
goldens. If you watch puppies of those in the show ring going away from you,
you will see suspicious movement, and that is a pretty good indicator of dysplasia.
Interestingly, Norwegian elkhounds as a breed have mediocre hips, but it appears that no
one told the dogs that was supposed to slow them down. The problem on X-ray is
relatively shallow sockets, but most do not develop disabling arthritis.
Maybe they have exceptionally good ligaments?
The prototypic platform for our modern dogs is a smallish wolf. Now, both wolves and coyotes are relatively lightly muscled for size of their skeleton. That is, the bones are robust in comparison to the muscle and other weight-producing parts of the body. Remember that a wolf sometimes has to body-slam a running deer. We know well that dogs that deviate in particular directions from the skeleton:weight ratio of wolves are more prone to hip dysplasia. So all the giant breeds are disasters in terms of hips on most individuals. In breeds relatively similar in height and length to wolves, the rule of thumb is that the lightly built breeds have better hips than heavier breeds. Thus, greyhounds seem free of dysplasia, while labs and goldens are cursed. Siberian huskies mostly have good hips, while Alaskan malamutes are more frequently dysplastic.
Most small dog breeds are thought to be free of hip dysplasia. So which is the Cardigan, large breed or small breed? Perhaps it is a sturdy small breed. If one thinks of what a Cardigan would be without dwarf legs, it would be middle-sized. The Cardigan has muscles of the hind leg which are unusually wide in relation to their length. It appears that, when the leg bones shortened, the muscle mass stayed the same, and therefore the only solution was very wide muscling. Maybe that contributes to the relative stability of Cardigan hips. It is also possible that the great athleticism of Cardigans helps. No one told the dogs that having short legs was a disadvantage, but they surely have compensated by working a lot harder hence the hardness of the muscles of the hind leg of working corgis.
Conclusion: There is a lot more to hip dysplasia than just the morphology of the joint itself. There is a lot to think about!! Then, you must put X-Rays as an item in the budget. Finally, given all the features we try to select for, how important are good parent X-rays? There are probably over 50 features we select for, some have high priority, some lower. But, surely PRA clearance, avoiding monorchidism, and other medical problems are just as important as good hip X-rays. I wish we were all so lucky as to find dogs that passed all of these, but it the real world, no individual dog is perfect. Then, we want to select for sound structure, all over the dog, not just the hips. And we want it to look like a Cardigan corgi.
The choices are never easy.