Canine Hip Dysplasia - Risk Factors
(Continued article ... page 2 of 6)
| Definition | Risk Factors | Effects |
| Symptoms | Diagnosis | Prevention |
Risk Factors for Hip Dysplasia
The basis for CHD is the dog’s genetic makeup, which can be measured by what is termed the Heritability Factor. Heritability is measured on a scale from zero to one, with a condition totally unrelated to genetics (such as a traumatic injury) measured at zero and a condition entirely determined by genetics (such as gender) measured at one. Studies have shown that CHD's Heritability factor ranges from .25 to .85, which indicates a significant genetic contribution. Therefore, if the parents are carrying genetic material for CHD, the offspring is guaranteed at least to carry the gene. And the greater the Heritability Factor for loose hips or malformed bone or abnormal muscle mass from the parents, the greater the chances for hip dysplasia in the offspring.
The expression of hip dysplasia in any dog has other determinants, though; genetics are only one factor in the total picture. The effect of the developing dog's environment does play a role in the observable signs of dysplasia, although just as with the genetic component, the effects of environment are variable and not completely understood. In other words, it is possible for a dog with known genetic components for hip dysplasia not to show any clinical signs of trouble if the environmental factors are favorable, or not to show observable signs of it until middle or old age.
Genetic CHD factors in dogs are distributed unevenly across certain breeds. CHD is primarily a disease of large and giant breeds, though it can occur in medium-sized breeds and rarely in small breeds. It primarily afflicts purebreds, although it can happen in mixed breeds, particularly a cross of two dogs that are prone to developing the disease. German Shepherds, Labrador Retrievers, Rottweilers, Great Danes, Golden Retrievers, and Saint Bernards appear to have a higher incidence, but these are all very popular breeds and may be over-represented because of their popularity. Other high-risk breeds include the: American Bulldog, American Staffordshire Terrier, Beagle, Bernese Mountain Dog, Bloodhound, Bouvier des flandres, Boykin Spaniel, Briard, Brittany, Bulldog, Bullmastiff, Chesapeake Bay Retriever, Chow Chow, Clumber Spaniel, Coonhound (Black and Tan), Coton de Tulèar, Curly Coated Retriever, English Setter, English Springer Spaniel, Giant Schnauzer, Gordon Setter, Irish Water Spaniel, Kuvasz, Neapolitan Mastiff, Newfoundland, Norwegian Elkhound, Old English Sheepdog, Otterhund, Polish Lowland Sheepdog, Portuguese Water Dog, Pudel Pointer, Pug, Rottweiler, Shih Tzu, Spanish Water Dog, Staffordshire Terrier, Sussex Spaniel, Welsh Corgi, and Welsh Springer Spaniel. Greyhounds and Borzois have a very low incidence of the disease.
Formula for Determing a Dog's Predisposition to CHD
The formula for determining any dog’s predisposition to CHD is complex, taking into account not only genetics and breed but a whole host of contributing factors. It must be stated that some researchers believe that genetics is the only factor involved, whereas others think genetics contributes less than 25% to the development of the disease. The truth probably lies in the middle. If there are no genetic carriers of hip dysplasia in a dog's lineage, then it will not contract the disease. If there are genetic carriers, then it may contract the disease. The incidence of hip dysplasia can be greatly reduced through a certain type of selective breeding, as well as increased. However, the disease cannot be completely avoided through selective breeding. In other words, if two dysplastic dogs are bred, the offspring are much more likely to develop the disease, but will not all have the same level of symptoms, or even necessarily show any symptoms. The offspring from these dogs will, however, be carriers and the disease may show up in their offspring in later generations. This is why it can be difficult to eradicate the disease from a breed or specific line, or even to produce the conditions under which the disease would be guaranteed to occur. The following factors affect a dog to varying degrees:
Nutrition: A key contributor to CHD is obesity. The effort of carrying extra weight will exacerbate degeneration of the joint in a dog with a loose hip. Overweight dogs are therefore at a much higher risk. Another factor that might increase the incidence is rapid growth in a puppy during the ages from three to ten months. Experimentally, the incidence has been increased in genetically susceptible dogs when they are given large-quantity/large-calorie diets. A 1997 study showed that Labrador Retriever puppies that were fed a high-protein, high-calorie diet free choice for three years had a much higher incidence of hip dysplasia than their littermates who were fed the same high-calorie, high-protein diet, but in an amount that was 25% less than what was fed to the dysplastic group. As might be expected, however, the free choice group was significantly heavier at maturity, averaging 22 pounds heavier than the control group.
There have also been studies examining protein
and calcium levels and their relationship to hip dysplasia. These studies found
that increased amounts of calcium and protein in the diet were correlated with
a higher incidence of hip dysplasia. But once again, these studies compared puppies
fed greatly increased amounts over normal recommended values to animals fed decreased
amounts. They failed to compare puppies fed a normal amount of food that had
the recommended amount of protein, fat, and calcium to those fed a diet with
slightly less protein, fat, and calcium (similar to those “large breed puppy
foods” that are now flooding the market). No studies link an increased incidence
in hip dysplasia in dogs fed a normal diet of commercial puppy food versus a
specialty diet formulated just for large breed puppies.
Some reports indicate that in puppies a restricted calorie intake could restrict
the growth rate, and in turn lessen the likelihood of the dog developing hip
dysplasia. The problem with this is that some restricted diets restrict the fat
and protein content and increase the carbohydrate content of the food. A pet
owner’s real goal should be to keep growing pups from becoming overweight. Restricting
fat and protein in a growing pup can be a disaster. A high-quality, meat-based
diet is absolutely necessary for growing pups, as long as the owner does not
feed the puppy so much that it becomes overweight.
Exercise: A young, growing dog with a genetic makeup for CHD will be more likely to develop arthritis and have more difficulty in the long term if it is highly active physically. Climbing stairs, jumping, and running can all subject the growing hip structures to unwarranted stress and trauma and increase the risk of future discomfort for the dog. The effects of excessive activity are worsened in an overweight pup. (In a normal, growing dog, these activities will not cause hip dysplasia.)
In short, it appears that dogs that are genetically susceptible to the disease may have an increased incidence of disease if they over-exercised at a young age. At the same time, we know that dogs with large and prominent leg muscle mass are less likely to contract the disease than dogs with small muscle mass. So, exercising and maintaining good muscle mass may actually decrease the incidence of the disease. Moderate exercise that strengthens the rump, or gluteal muscles, such as running and swimming, is probably a good idea, whereas activities that apply a lot of force to the joint, such as jumping during a game of Frisbee, are contraindicated.
The Pectineus Muscle can contribute to the worsening of hip dysplasia. In a dog with a strong genetic background for CHD, the microscopic makeup and contractibility of the Pectineus Muscle are strikingly different from the corresponding muscle of a normal dog. The theory is that a tight or inelastic Pectineus Muscle causes tension in such a way that the force tends to pull the head of the femur away from the acetabulum, increasing looseness in the joint. I have had good results in about 50% of the cases in which I have surgically excised a portion of the Pectineus Muscle. The patients were more comfortable and mobile almost immediately. This Pectineal Myotomy surgery has no effect on the arthritic changes in the hip joints, but it can make the dog more comfortable.
Surfaces: There is no scientific
proof that surfaces have an impact on the disease, but many observers conclude
that pups reared, especially during the nursing period, on slippery surfaces
such as newspapers will be prone to hip difficulties. Smooth concrete or wood
surfaces may not cause dysplasia, but they can make a bad situation worse. Better
surfaces for newborn pups are blankets or towels—surfaces they can grip.
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