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Hereditary defects in Australian Shepherds

 

All breeds of dog, including Australian Shepherds, suffer some degree of hereditary defects and diseases that cause conscientious breeders to have nightmares. Some lucky breeds are relatively free of these inherited conditions, while others are riddled with them – it is almost impossible, for instance to find a collie which is both free of eye defects and the genes which cause them. Skeletal disorders are also common in dogs – hip dysplasia is found very frequently in some giant breeds and many toy breeds are often afflicted with patellar luxation (slipping kneecaps). Blood clotting disorders (hemophilia and Von Willebran’s Disease) also occur in a number of breeds.

These things are the main genetic nightmares, though others occur with greater of lesser frequency in one or more breeds. An example would be the cleft palate syndrome being studied in a family of dogs belonging to the Genetics Committee. This inheritable defect has been traced to a single individual and has not been identified elsewhere in our breed or in any other breed.

Aussie breeders have been able to sleep fairly peacefully – so far. Hip dysplasia does occur, but many people have been regularly screening for it for as much as 20 years now. Therefore, it has not become the big problem in our breed that it is in some others. Eye defects, on the other hand, are a problem that seems to be on the increase. We are getting more and more reports of dogs afflicted with various kinds of eye problems. (Part of this increase may stem from the fact that people are becoming more aware and are checking their dogs more often and at a younger age.)
HIP DYSPLASIA

Hip Dysplasia is, in brief, the failure of the head of the femur (thigh bone) to fit firmly into the acetabulum (hip socket). It causes a wide range of steady or occasional lameness and movement irregularities. In very bad cases it can cripple the dog.

Affected dogs must have their physical activities limited to a greater of lesser degree and, in the worst cases, may require expensive surgery to relieve the dog’s pain an deniable it to more around.

The condition is no solely caused by poorly formed or positioned bones – the quality and quantity of muscling and tendons are now felt by many researchers to play a role. Environment (mostly nutrition and the level of exercise) also contributes to the presence or absence of hip dysplasia.

HIP DYSPLASIA IS A POLYGENIC INHERITED DISORDER, THE EXPRESSION OF WHICH MAY BE AFFECTED BY ENVIRONMENTAL FACTORS.

In plain English, this means that many different genes contribute to factors that lead to hip dysplasia. This makes it impossible to accurately predict how and when it will occur. It can crop up in families of dogs which have been free of it for generations and it is possible for affected animals to have unaffected offspring.

Hip dysplasia can only be accurately diagnosed through radiographic examination of the hip joints – x-rays. The dog should be anesthetized or tranquilized so that it is relaxed, then laid flat on it’s back with the hind legs stretched back and parallel for the x-ray. Other positioning can either conceal signs of the disorder or give the impression of problems that do not actually exist.

Once the x-ray is taken, official grading and certifying is done by the Orthopedic Foundation for Animals (University of Missouri – Columbia, Columbia MO 65211). The OFA will submit your x-rays to a panel of three veterinary radiologists for evaluation and they will determine the rating for your dog’s hips.

Sound hips will be rated Excellent, Good or Fair and the dog’s owner will receive a certificate stating this, which can be used as proof of soundness. A dysplastic dog will be graded Mild, Moderate or Severe and, of course, receives no certificate. A few dogs will be graded Borderline – which means that the experts aren’t quite sure. If this happens, wait 6 to 8 months, take another x-ray and submit it.

IF YOU HAVE A DYSPLASTIC DOG, DO NOT BREED IT!

Even though you might get clear pups, with a lucky breeding, those pups will be carrying a whole collection of genes for the condition and will very likely pass it to their offspring.

There is no need to eliminate the parents of an affected dog from your breeding program providing that they are 1.) free of hip dysplasia themselves and 2.) do not produce it on a regular basis, especially with different mates. Any animal that has produced several dysplastic offspring from different crosses should be pulled from breeding.

The wisest thing to do is not to breed a dog until its hips have been certified – this means after two years of age. The reason OFA will not certify hips until that age is that they discovered early on that hips sometimes change if x-rayed earlier and a dog which at a year or 18 months grades clear, will by two years be dysplastic. ‘Preliminary’ x-rays may give some indication of the condition of the hip joints, but they are no guarantee that a dog is sound.

There are several myths about hip dysplasia floating around. You CAN NOT be sure that a dog is dysplastic simply by watching it move or looking at its rear conformation. There have been Best In Match winners and high-scoring trial dogs which have been dysplastic. Nor does ‘frogging’ (the tendency to lie down with the rear legs stretched straight behind) indicate the absence of hip dysplasia

EYE DEFECTS

Eye defects are our biggest genetic nightmare. A variety of eye problems, which are probably hereditary, have been found in Aussies. That’s the good bad news. The bad news is that we do not yet know exactly how these defects are passed. They are most certainly not simple dominants (the easiest type of trait to eliminate) and they are not necessarily simple recessives, either. Multiple genes, modifiers and gene series all may play a part in different defects.

Heritability has been determined, at least tentatively, on some of these defects in some breeds. But this is no guarantee that the defects are passed the same way in Aussies.

DOGS WITH EYE DEFECTS SHOULD NOT BE USED FOR BREEDING!

Until we can prove scientifically how the traits are passed, the parents of defective animals should be eliminated from breeding programs IF they produce significant numbers of affected offspring, especially from different mates.

Homozygous Merle Eye Defects

These are the easy ones to deal with, either don’t do merle to merle breedings or cull homozygous (‘white factored’ or ‘defective’) merle pups. The catch is that sometimes, in very rare instances, a dog which appears to be a ‘normal’ heterozygous merle is actually homozygous and will have some or all of the associated eye defects.

If a merle dog is diagnosed as having any of the defects listed below, ask these questions:

  • Are both of this animal’s parents merle?
  • Is this animal out of parents with little or no white or from a line where little or no white is the norm?
  • If the dog has been bred, has it never produced a solid colored pup?
  • If the answer to all of these questions is ‘yes’ you might be dealing with a homozygous merle.

Defects found in homozygous merles are as follows:

  • Micropthalmia – abnormally small eyes.
  • Subluxated Pupils – pupils that are off-center in the iris.
  • Iris Colobomas – abnormal holes in the iris. (These can occur independently of merle homozygosity.)
  • Persistent Pupilary Membrane – a fetal covering of the pupil which fails to disappear by five weeks of age.
  • Cataracts – opacities on the lens. (These can occur independently also.
  • Optic Disc Colobomas – irregularities or pits found within the optic disc. (These can occur in Collie Eye Anomoly, too.)
  • Staphlomas – bulging rear wall of the eye. (This also occurs in Collie Eye Anomoly.)
  • Retinal Dysplasia – detached retinas of both eyes . (This condition can occur in Collie Eye Anomoly.)
  • Choroid Hypoplasia – incomplete development of the vascular tissue (blood vessels) in the back of the eye. (Another defect found in Collie Eye Anomoly.)
  • All of these defects affect vision to a greater or lesser degree, which is why many homozygous merles see poorly or are blind.

Collie Eye Anomoly

A dog with Collie Eye Anomoly will suffer from Staphloma, Optic Disc Coloboma, Retinal Dysplasia and/or Choroid Hypoplasia. The condition is present at birth and remains the same throughout the dogs life, though some signs may be obscured by natural pigment in the back of the eye as the dog matures.

IT IS VITAL THAT EVERY PUP IN EVERY LITTER BE CHECKED FOR COLLIE EYE ANOMOLY BEFORE IT IS FOUR MONTHS OLD!

The condition may not noticeably affect a dog’s vision except in severe cases, but it is hereditary and is being identified is Aussies with increasing frequency. If you wait until you decide whether or not a young dog is going to be a show or breeding prospect to check its eyes, it may be too late to detect the condition.

Cataracts

Hyloid Arteries

These arteries are embryonic structures of the eye–small arteries that extend from the optic disc to the lens before birth. Normally, they disappear by or shortly after birth, but sometimes all or part of them will remain.

A remnant hyloid artery is a small tab of tissue which connects to the back of the lens, a persistent hyloid artery is complete but no longer carries blood, and a patent hyloid artery is complete and functional. The presence of all or part of a hyloid artery is sometimes associated with scarification or opacities of the lens, varying from minor to moderate.

Hyloid arteries are not at present considered to be hereditary, but the Genetics Committee has noted them with unusual frequency in eye defect dogs for a chance condition and their occasional association with potentially vision-impairing lens opacities is a cause for concern. The condition will remain the same throughout the dog’s life.

Iris Colobomas

Iris colobomas are probably the most easily recognized eye defect found in Aussies–the evidence is right in the dogs pupil for anyone to see and, unlike the other conditions listed here, does not require special instruments to detect and diagnose. It is also probably the lease serious eye defect in our breed.

Iris colobomas cause very little disturbance of a dog’s vision, except in serve cases (large colobomas) where the iris is unable to contract significantly, and control the amount of light that enters the eye. Since dogs do not fine-focus their vision like we do, most colobomas affect them very little.

Iris colobomas are present at birth and remain the same throughout a dog’s life. Their mode of inheritance is known and may be merle-linked.

Progressive Retinal Atrophy

Progressive retinal atrophy (PRA) is the progressive degeneration of the retina in the eye. (Non-progressive atrophy can be caused by disease.) A dog with PRA starts showing signs between 8 weeks and 6 months of age. As the retina deteriorates, the dog’s vision becomes gradually worse until it is blind. Most experts agree that this disease is always recessive. It is not common in Aussies and generally not included as a breed problem, but the Genetics Committee is aware of one Aussie that was diagnosed as having PRA. PRA diagnosis requires more than one examination, unless the case is very advanced.

Diagnosis of Eye Defects

EYE DEFECTS CAN BE ACCURATELY DIAGNOSED ONLY BY CERTIFIED VETERINARY OPTHAMOLOGISTS !!!

Checks should be made as early as 6 weeks (dependent upon puppy cooperation) and should be redone on an annual basis thereafter. Certifications on clear eyes are done by the Canine Eye Research Foundation (CERF), P.O. Box 15095, San Francisco, CA 94115, and must be updated annually.

WHAT CAN YOU DO ABOUT GENETIC DEFECTS IN YOUR AUSSIE?

1. CHECK ALL STOCK FOR HIP DYSPLASIA AND EYE DEFECTS.

  •  Xray hips at two years and get OFA certification (the only positive proof an animal is free of hip dysplasia.)
  • Check eyes on an annual basis, starting at 6 to 8 weeks.
  • Check all puppies you produce which survive at 6 to 8 weeks.

2. ELIMINATE AFFECTED STOCK FROM YOUR BREEDING PROGRAM.

3. ELIMINATE PARENTS OR OTHER CLOSE RELATIVES OF AFFECTED STOCK IF THEY PRODUCE SEVERAL AFFECTED OFFSPRING, ESPECIALLY FROM DIFFERENT MATES.

4. AVOID THE ‘OSTRICH SYNDROME.’ Don’t stick your head in the sand and hope it will go away. It won’t – it will only get worse if you do

5. STUDY. Learn all you can about canine genetics and heritable defects and diseases – of all breeds, not just Aussies. The other guy’s problem may be ours tomorrow.

 

 

 
 
 
 
 
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