边境牧羊犬的健康与遗传性疾病(美国边境牧羊犬协会)

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英文原文如下.

The Border Collie stands alone in its exceptional ability to work livestock. ABCA defines the breed by this working ability.  The main goal of any Border Collie breeder should be to produce sound, useful, working dogs. While Border Collies also excel in many non-herding activities, they should be bred primarily to work livestock. The ultimate responsibility for maintaining the integrity of this as yet unspoiled breed lies with the breeders. Breeders are urged to take this responsibility seriously. Puppy buyers are encouraged to buy only from those breeders who do take this responsibility seriously.

  

Both breeders and buyers should understand there are risks involved in any breeding, regardless of the amount of care taken to avoid problems. In order to ensure a healthy gene pool for future generations of Border Collies, breeding prospects should be evaluated with reasonable concern for potential problems and realistic goals for what will be produced. The breeding prospect should be considered as a whole being, with positive and negative aspects of the individual being weighed and balanced for an overall picture of a dog's suitability. Breeding should be undertaken with thoughts of what the parents have to offer to their pups that could benefit the breed.

  

Genetic Diseases
  

To be considered a genetic disease, a health problem needs to have been demonstrated to be heritable, 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.

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Collie Eye Anomaly (CEA) CEA is a congenital disorder where the parts of the eye, particularly the retinal area, do not develop normally. The severity of the disease ranges from no visual impairment to blindness. It is not a progressive disease and affected dogs normally only have mildly impaired vision. Puppies should be tested before 12 weeks of age, if possible, by a Diplomate of the Association of Canine Veterinary Ophthalmologists (DACVO) because some dogs have a mild form of the disease called "go normal", where normal tissue grows over and covers up the diseased area as the dog matures. Identification of "go normals" is important, as these dogs are affected with CEA and will produce affected puppies just as if they had full blown expression of the disease.

  

This disease is much more straightforward than HD in both its inheritance patterns and in our ability to control it. CEA is an autosomal recessive disorder. Autosomal means it is passed on and expressed equally in males or females. Recessive means a dog may carry a bad CEA gene and pass it on to its offspring without having the disease itself. A dog is defined as Clear if it has no bad CEA genes. A dog is defined as a Carrier if it has one bad CEA gene and one normal gene. Both the Carrier and the Clear dogs will be unaffected and will test negative for CEA in the eye exam. A dog is defined as Affected if it eye tests positive for CEA. The outcomes of the different crosses of these dogs are as follows:

  

Clear X Clear = 100% CEA Clear puppies

Clear X Carrier = on average, 50% Clear, 50% Carriers

Clear X Affected = 100% Carriers

Carrier X Carrier = on average, 25% Clear, 50% Carriers, 25% Affected

Carrier X Affected = on average, 50% Affected, 50% Carriers

Affected X Affected = 100% Affected

  

The incidence of CEA in Border Collies in North America is about 2.5%. The carrier rate is probably ten times that figure, or 25%. Until very recently, the only way to know if a dog was a Carrier was for it to produce an Affected puppy. Since there are so many unknown Carriers, that meant there was no way to prevent inadvertantly producing Affected puppies.

  

The ABCA, with support from other working Border Collie groups and owners, funded Dr Gregory Acland from the James A. Baker Institute for Animal Health, Cornell University, to develop a DNA test for CEA. That project was successful, and since the beginning of 2005 a test has been available which can determine whether a dog is Affected, a Carrier, or Clear.  The test is being administered through OptiGen, LLC, and further details about it can be obtained on their website at www.optigen.com.  The ABCA recommendations regarding CEA will shortly be updated in response to the availability of this new test and the statistical data so far gleaned from it..  In the meantime, the recommendations are as follows:

  

--For owners of known Carriers (unaffected dogs that have produced a CEA affected puppy) - ABCA recommends that anyone who inquires about the dog's progeny or as a mate be told that it is a Carrier. It also recommends that people who have any of this dog's progeny be informed that all its offspring have at least a 50% chance of also being a Carrier even if the other parent is neither a Carrier nor Affected.

-- For breeders of a litter in which one parent is a known Carrier - The ABCA recommends that all puppies in the litter have an ophthalmic examination by a DACVO by 12 weeks for accurate detection of "go normal" CEA. If this examination cannot be done, it is recommended that the puppy buyers be informed that they must determine from an ophthalmic examination that the dog is not affected with CEA before it is considered for breeding, as the progeny of affected dogs are not eligible for registration.

--Do not breed two known Carriers together, as this will likely result in Affected puppies.

--Do not breed CEA affected dogs. These dogs and their progeny are not eligible for registration with ABCA at this time.

  

Epilepsy Epilepsy is a disease characterized by seizures or "fits" as they are sometimes called. Although it's clear Border Collies can be affected with epilepsy, the incidence and heritability in our breed are unknown. The ABCA is conducting a health survey to determine the extent of this problem in the breed. Please help us in this effort, whether you have an affected dog or not, by responding to the health survey on ABCA's web page listed below.

  

Since there can be many causes, determining why a dog has seizures is a complex process. The diagnosis of primary epilepsy is made based on negative results for other causes of seizures. Therefore, it is a diagnosis made by exclusion rather than by a specific test. Since we have little breed-specific information to go on, ABCA breeding recommendations concerning this disease are based on those for other affected breeds in which the disease is more well-defined. Recommendations are: Do not breed affected dogs. If two unaffected dogs produce an affected puppy, do not repeat that cross.

  

Genetic diseases not considered to be a significant problem in the breed at this time:

  

Progressive Retinal Atrophy (PRA) PRA is a progressive disease where tissue in the retina of the eye is destroyed. It may initially be noticed as decreased ability of the dog to see at night, and may eventually progress to total blindness.

  

Despite the persisting impression that this genetic disease is prevalent in the breed, extensive investigation has shown the incidence of PRA in Border Collies in North America to be extremely low to non existent. Therefore, the ABCA does not currently consider it a major health concern.

  

Elbow dysplasia Elbow dysplasia is a general term used for what is essentially three different types of degenerative elbow disease. These diseases may occur singly or together and are thought to be caused by several different genes.

  

More and more owners are having their Border Collies' elbows evaluated each year. However, OFA reports a 0% incidence of elbow dysplasia for 210 Border Collies tested from January 1974-December 1999. ABCA does not consider elbow dysplasia a significant health problem in the breed at this time.

  

Common diseases with questionable heritable cause:

  

Osteochondritis Dissecans (OCD) OCD is a condition that occurs primarily in puppies between the ages of 4-9 months, but can also be found in older puppies. It is considered to be a common disease in rapidly growing dogs of large breeds. However, medium breeds such as the Border Collie can also have a high incidence of this disease. It is seen twice as often in males as in females. The shoulder joint is the most commonly affected site but it can be seen in stifles, elbows, hocks or other joints. The diagnosis is usually confirmed by x-ray of the involved joints.  In approximately one third of the cases of OCD, the disease is bilateral (in both joints). Occasionally, it is present in several different joints in the same individual. OCD is thought to be caused by a problem in the growth rate of the joint cartilage relative to the underlying subchondral bone.

  

Although the factors that cause OCD are not completely understood, direct factors considered to be involved in the development of OCD are rapid growth and trauma to the joint. Indirect factors affecting rapid growth include nutrition, hormones, and genetic predisposition to rapid growth and large size. Indirect influences that may lead to increased trauma to the joint include conformation and behavior, which are also influenced by heredity. Therefore, the genetic link for most types of OCD is considered to be indirect, that is, an inherited tendency. Certain sites for OCD lesions, such as the elbow, appear to have a greater direct genetic contribution and a higher heritability than other sites, such as the shoulder. The most important contributing factor in OCD of the shoulder, the most common site, is thought to be trauma. OCD can best be prevented in growing puppies by controlling the main precipitating factors, overnutrition and activities that could result in injury to the joints.

  

Because factors involved in the heritability of OCD are considered to be indirect, and therefore not easily controlled by selection, ABCA has no breeding recommendations for OCD at this time.

  

Common diseases with no known heritable contribution:

  

Focal/Multifocal Acquired Retinopathy (FMAR): This inflammatory eye disease is common in many working breeds and is probably the most frequently seen retinal lesion in Border Collies. Sometimes called "distemper scars" or "worm scars", it is characterized by lesions in the retina that can accumulate over the years, often leading to impaired vision and sometimes leading to blindness.  The lesions have a typical "bull's eye" pattern, and tend to be asymmetrical (affect one eye more than the other).  The age of onset and rate of progression varies greatly from individual to individual.  Males are more frequently affected than females.  The characteristics of this disease strongly suggest environmental cause; no heritable pattern has ever been established for its occurrence.  Its pathology clearly distinguishes it from  PRA, although it is sometimes mistaken for PRA, especially in the later stages of the disease.

  

  

In summary, this brochure is meant to provide a brief description of some common diseases, some current knowledge about their heritability in our breed, and relevant breeding recommendations. Please remember, diseases present in Border Collies are not limited to those discussed here.  Also remember, these recommendations are guidelines, not restrictions.  Keep track of updated and more in depth Border Collie health and genetics information by checking the ABCA web site at www.americanbordercollie.org .

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