For centuries man has been supervising the breeding of dogs, and exercising his power to choose the characteristics he wished to preserve and eliminate. This process, known as selective breeding, resulted in the many individual breeds of dogs that are known today. Gradually, as breeders became aware of the concepts of genetics, they applied basic genetic principles to their breeding programs. By combining the art of selection with the knowledge of science, breeders were able to refine the breeds of their choice.
Much importance has been placed on pedigrees and much success has been derived from the breeding of closely related dogs that share desirable genetic traits. It was inevitable that, along with the desirable traits, there have come undesirable traits which may take several generations of breeding to manifest themselves. When these undesirable traits finally do surface, breeders must acknowledge that their seemingly normal dogs may transmit defective genes to their offspring and perpetuate the undesirable trait in the breed.
No breed of dog is totally free from inheritable genetic defects, but few breeds have had the good fortune of the Siberian Husky. Not only is the individual dog generally healthy and of good temperament, but throughout the years there has not been an abundance of genetic issues. Additionally, the USA's national breed club, the Siberian Husky Club of America, Inc. (SHCA), has maintained a watchful eye for potential genetic problems and has taken positive action in those instances when the general health and well-being of the breed has been challenged.
Since 1965, the SHCA has maintained a committee whose task is to be aware of the start of genetic problems in the breed and to alert breeders before the defect has begun to spread. Two major conditions have been uncovered in this manner and, in each instance, the board of directors of the SHCA has instituted practical guidelines in order to enable breeders to decrease the spread of the inheritable disorder. These two areas of greatest concern are canine hip dysplasia and inheritable eye disease.
From January 1994 through December 1998, a total of 12,087 Siberian Huskies have been evaluated by OFA for hip dysplasia. Out of this total, 30.5% of the dogs have received "excellent" hip ratings, and only 2.2% have been dysplastic. (Please note that radiographs showing hip dysplasia may not have been mailed to the OFA on the advice of the referring veterinarian.)
Out of the 114 breeds of dogs at risk for hip dysplasia, the Siberian Husky is one of the breeds least affected ranked at #111 out of a possible 114 based upon evaluations from 1974 through 1994. This impressive ranking has been achieved through the cooperation of breeders who followed the breeding program guidelines established by the OFA and the SHCA to decrease the incidence of hip dysplasia.
The Siberian Husky has been one of the few breeds that had a dramatic decrease in the incidence of hip dysplasia from 1980 through 1995. The breed has experienced a change of + 42.1% in the number of OFA "excellent" dogs, and a - 55.6% change in the number of dysplastic dogs.
What is canine hip dysplasia?
Hip dysplasia is an abnormality of the hip joint in which the head of the thighbone (femur) does not fit properly into its pelvic joint socket (acetabulum). This condition, while not present at birth, develops during the first two years of the dog's life. It is often progressive, causing inflammation, pain, and arthritis of the affected hip. It is aggravated by strenuous exercise and, sitting up, lying down, or climbing stairs.
This disorder afflicts dogs of both sexes, and may be present in one or both hips. The condition may range from mild to severe, and clinical signs may become more evident in dogs under one year of age. It is regarded with utmost concern in our breed because the dysplastic Siberian Husky cannot do the work for which it was bred, nor can it exhibit the freedom and effortlessness of movement so highly prized in the show ring and on the sled.
Canine hip dysplasia is an inheritable disease. Its mode of inheritance is termed "polygenic," meaning that it is due to a combination of multiple genes. Because of the polygenic nature of this disorder, some normal dogs produce a percentage of dysplastic offspring. The breeding pair, although physically normal, may each transmit some of the dysplastic genes to their offspring, thus the offspring may receive a combination of complementary genes from both parents which may cause hip dysplasia. The division of defective genes is very uneven, with one parent contributing more defective genes than the other. Environmental factors such as a high caloric diet during the rapid growth phase of a puppy can exacerbate the changes in dysplastic hips, but cannot create a dysplastic dog.
How is hip dysplasia diagnosed?
Accurate diagnosis can be established through radiographic examination by a veterinary radiologist. The dog is sedated and the hind limbs are rotated and extended to allow the proper positioning of the hips and femurs. It is recommended that bitches in heat or in pregnancy not be radiographed since the hormones may interfere with joint laxity. After the films are taken, they are mailed to a hip registry organization such as the OFA or Penn Hip in the USA. In Australia The AVA run the Hip Dysplasia Scheme. Radiographs are read and scored using the British Veterinary Association scoring system.
The BVA Scoring system
All radiographs submitted are assessed by means of scoring. The hip score is the sum of the points awarded for each of nine radiographic features of both hip joints. The lower the score the less the degree of hip dysplasia present. The minimum (best) score for each hip is zero and the maximum (worst) is 53, giving a range for the total of 0 to 106 The average score of the breed, or the 'breed mean score', is calculated from all the scores recorded for a given breed and is shown alongside its range thereby giving a representation of the overall hip status of the breed. All breeders wishing to try to control HD should breed only from animals with hip scores well below the breed mean score. Sires (fathers) to be bred from should only be ones whose progeny (offspring) have achieved consistently low scores. The same selection procedure should be used for bitches for breeding, since the use of animals with higher than ideal scores may make the risk of producing offspring with high scores much greater. This circumstance is not only disappointing and potentially costly in terms of compromised breeding plans, but may lead to subsequent civil court action. For the hip scoring scheme to be meaningful and successful in the attempt to control this serious disease it is important that all radiographs taken under the scheme are submitted for scoring, whatever the apparent state of the hips, in order that the information gathered is as relevant as possible. It is only by this means that proper conclusions may be drawn by the scheme's statisticians, geneticists and veterinary advisers. It is not hard to understand why things happen so quickly and how critical a whole series of factors in the dog's life are, when realising some animals treble their size and weight during a three- month period of adolescence. Getting all the many nutritional needs in the right quantity, to the right place and at the right time requires a mastery of logistics. However, it has to be realised that this apparent basic requirement overlays the parts played by inheritance and other factors, for example the type of exercise taken and the degree of body weight.
The OFA Hip Registry(USA)
The Orthopedic Foundation for Animals (OFA) is a private, non-profit organization based in the USA which disseminates information on orthopedic and genetic diseases to the public. It is the world's largest all-breed hip registry, with over 475,000 dogs. After a veterinarian takes an x-ray of the dog's hips, the x-ray is mailed to OFA for hip evaluation. The radiograph is then evaluated independently by three board certified veterinary radiologists. The final hip grade is decided by a consensus of the three independent radiologists. Only dogs over 24 months of age that receive "excellent," "good," or "fair" evaluations will receive an OFA registry number. This number is reported to the AKC and parent breed club. Abnormal hips are only reported to the owner and referring veterinarian. Dogs under 24 months of age can have a preliminary hip evaluation, but a registry number will not be assigned until new radiographs have been resubmitted at 24 months of age.
The OFA maintains a hip registry open to the public and is available on the OFA website at the following address: www.offa.org
Preventing Hip Dysplasia
Only those dogs which have been given a low hip score or certified free from hip dysplasia by the OFA should be used for breeding. Whenever possible, close relatives to dysplastic dogs should not be used for breeding even if they are physically normal. Vital to the program is the establishment of "pedigree depth" for each individual stud dog or brood bitch. In order to establish pedigree depth, the parents, grandparents, and all close relatives of the stud dog or brood bitch should also be Hip Scored or certified by the OFA. Most good breeders have already adhered to this protocol and have had an admirable record of dysplasia-free stock for generations of dogs.
Although there are many possible eye defects, only three are of current concern in the Siberian. These are hereditary or juvenile cataracts, corneal dystrophy, and progressive retinal atrophy. Each disorder is present in a different portion of the eye, and will occur in any eye color. Eye defects in the Siberian Husky are serious and should not be understated or overlooked.
Of the three major eye diseases of the Siberian Husky, hereditary cataracts are the most common, followed by corneal dystrophy, and progressive retinal atrophy. A statistical report conducted by members of the American College of Veterinary Ophthalmologists in 1999 provided the following information regarding the Siberian Husky. Out of 1345 Siberian Huskies examined, a total of 107 dogs had inheritable cataracts (8%), a total of 44 dogs had corneal dystrophy (3%), and 4 dogs had progressive retinal atrophy (less than 1%).
Hereditary Cataracts & how they are transmitted
Hereditary or juvenile cataracts are manifested by opacity in the lens of a young dog as early as 3 months of age. These cataracts are different from the non-hereditary cataracts affecting aged or senior dogs. The function of the lens of the eye is to focus the rays of light so that they form an image on the retina. An opacity or cataract on the lens causes less light to enter the eye and sight can be diminished. A cataract can cause a mild decrease in eyesight to complete blindness in severe cases. Cataracts can further be classified by location and stage of development. The most common hereditary cataract in the Siberian Husky occurs on the posterior region of the lens. It is not uncommon for a cataract to develop in one eye months before the other eye shows the effects of the disease. Recent DNA research indicates that juvenile cataracts may be carried by a recessive gene. Genetic research is presently under way to develop a simple DNA test to identify dogs and bitches that carry the recessive gene for cataracts.
Corneal dystrophy affects the cornea or the outer transparent portion of the eyeball. In most cases, Siberian Huskies with this disorder have an abnormal collection of lipids in the clear cornea of the eye which results in a hazy or crystalline opacity. Ophthalmologists describe the location of the opacity as anterior, mid, or deep stromal. The Siberian Husky is prone to deep stromal dystrophy which involves triglyceride deposits. Annular dystrophy also occurs and appears as a doughnut shaped opacity in the peripheral cornea. Corneal dystrophy is usually seen in young adult dogs and may affect females more than males. Vision is seldom affected and no effective therapy for the condition exists at this time. Recent genetic tests are suggesting that a recessive gene with variant expression transmits this disorder.
Progressive Retinal Atrophy (PRA) & how is it transmitted?
Progressive retinal atrophy (PRA) affects the retina, the light-sensitive inner lining of the posterior part of the eyeball. The retina contains two types of specialized cells called rods and cones. The rods are necessary for sight in dim light or night light, and the cones are utilized in in bright light vision. The Siberian Husky has a unique type of PRA that is only found in Siberians and man. This type of PRA is called XLPRA (X Linked PRA) since it is transmitted through the "XX" chromosome of the female. It will cause a loss of night vision followed by a loss of day vision, eventually blindness. The recessive gene for XLPRA is situated on the "X" chromosome of the female. Females who inherit a defective gene on the "X" chromosome from one parent and a normal gene on the other "X" chromosome from the other parent, will not be seriously affected. They will be carriers with very subtle retinal defects and no loss of vision. The male puppy from a carrier dam will receive either a defective gene or a normal gene, depending on what chromosome was copied in the DNA replication. If he has the defective gene, the dog will be affected with PRA since males carry an "XY" chromosome. The disease in males can be devastating with loss of vision as early as 5 months of age.A genetic test is being developed to identify carrier females in the Siberian Husky. Once this test is available, XLPRA can be eliminated from breeding program
Prevention and Elimination
Research is now being conducted to develop DNA testing for both hereditary cataracts and progressive retinal atrophy. Until these tests are available, guidelines have been established to help breeders decrease the spread of heritable eye disorders. The guidelines are as follows: Every dog to be used for breeding Should be examined by Veterinary Ophthalmologist. This examination must be done during the year that the dog is to be used for breeding. Only dogs with normal examinations are to be used for breeding. Caution must be exercised in the use of those dogs that are closely related to affected dogs, or when a breeder suspects that an individual dog is producing a defect in its offspring. Though the dog itself may not exhibit signs of the eye defect, that dog should promptly and permanently be withheld from further breeding.