Where are we heading? And why should we bother?

‘Health Testing in the Chinese Crested Dog and the Future of the Breed’

Often we hear “My dogs do not need testing they have Clean Lines” unfortunately these people are only fooling themselves. No one can know if their dogs are clear of a disease unless they are tested for it. Another remark is “Oh they only test because they have problems” again, this is a smoke screen used by people who cannot or will not open their eyes to the issues in their breed.

If we are serious about improving the health of our chosen breed then we MUST test. Sticking our heads in the sand and blaming the new owners is not going to make the disease go away.

Testing and breeding from tested dogs will accomplish this as more and more DNA tests for diseases are uncovered.

 

The future of the breed is in our hands, if we do not care enough to breed only from the best and the healthiest then we are doomed to failure and the destruction of our breed. If we think that the Animal Liberationists will leave us alone when they have a stick to beat us with then we are even bigger fools.

Over the last 17 years I have seen an explosion of kennels around the world, some good and caring and some definitely not. We cannot allow “Puppy Farm” cresteds to be the norm for the breed, we cannot allow bad breeding practices to flourish while we do nothing. We have to be seen to be on top of our disease problems and being proactive in removing them from the breed. TESTING is the only way we can be sure our lines are clean and clear for the future breeders.

I know it’s a cliché but we are not the owners of the breed, we only care for it for a very short time and then it passes to other hands. Education of the new breeders is essential, education of the old breeders is even more important. How can we pass on what we do not practice ourselves? 

What kinds of tests are available?

Advances in Molecular genetic studies have resulted in the mapping of the canine genome. This means we can now accurately predict the genotype of a specific dog and test for animals that can be identified as having or carrying certain genetic diseases

The Chinese Crested has two forms of progressive retinal atrophy(PRA), which can eventually lead to blindness. One of these forms has a DNA test, prcd-PRA.

This DNA test can only tell you of the status of that one form of PRA, breeders and owners of the breed should still have regular eye exams to determine if any changes have occurred in the eye.

Glaucoma is another issues within the breed and is also detected by eye examination it can occur in conjunction with PLL or Primary Lens Luxation. This is an issue known in many other breeds as well such as Tibetan Terriers, Australian Cattle Dogs, and many other breeds. The lens is held in place in the eye by fibers known as zonules. If these zonules stretch or break, the lens can fall out of place, or luxate. When this happens it often requires immediate veterinary attention to remove the displaced lens and prevent painful secondary glaucoma, and sometimes loss of vision.

Not every case of Luxation is caused by PLL. Sometimes it can occur from blows to the head or strokes. DNA testing is one way to be sure it is not a genetic issue with that dog

 

The breed also suffers from another eye disease called Keratoconjunctivitis sicca or dry eye syndrome. This can be a painful condition and the dogs need surgery or careful home care to live with it. It is not currently something we can test for with a DNA test and it doesn't always show in the parent's physical eye exams. If can be caused by a trauma or a sever eye infection.

Along with eye issues we have Leggs Calves Perthe Disease, which is a degenerative bone disease that affects the head of the femur. Inheritance is still open for discussion. Hip scoring is one way to test for it as there is no current DNA test. Parents may not show the disease but still be carriers.

A vet should test patellas when the dog has his health check. 

 

Some testing sites available

http://www.asaplab.com.au/K9range.html

http://www.optigen.com/opt9_test_prachc.html

 

 

Using Carriers and Affected dogs

 FROM “where DNA tests have been developed for Simple Recessive Diseases
     Karen Hedberg BVSc  

 

Of the 400 odd diseases in the dog that are inherited or have significant inherited components, more than half are believed to be single gene defects, and around 70% of these, are inherited as in a simple autosomal recessive mode of inheritance.  

Simple autosomal recessive gene DNA test

With a simple autosomal recessive gene, the DNA test will clearly differentiate between affected, carrier and normal individuals. The beauty of this type of genetic test is that you do not need to lose any valuable animals from your breeding program. Outstanding examples of the breed that are otherwise sound can be retained even if they are affected once this type of test is available. All you need to remember to do is to always breed ‘up’.

 

Normal/clear dogs are usually given the ‘A’ pattern designation.

Carriers (heterozygous) are given the B’ pattern designation.

Affected dogs are given the C’ pattern designation.

Where ‘A’ = normal dominant allele and ‘a’ = affected recessive allele.

One allele comes from each parent.

 

 

When mating these dogs, mating two normal i.e. A to A will result in all A dogs, no testing required

With normal/clear A to carrier B dogs, 50% will be A and 50% will be B dogs – no affected dogs produced, only need to test those puppies that are retained to sort out the A from the B dogs, but this can be delayed if necessary until nearer breeding age (as no affected progeny).

With normal/clear A to affected C dogs, no testing is necessary, as all progeny are automatically B i.e. Carriers.

What you should try to avoid as much as possible is putting a carrier or an affected dog to anything but a normal/clear (A) dog.

 B-to-B matings will produce ¼ normal, ½ carrier and ¼-affected progeny therefore all progeny must be tested prior to sale (an expensive undertaking).

 Equally, B to C matings are very high risk as there will be 50% carriers (B) and 50% affected (C) progeny – again, all progeny must be tested prior to sale.

 Affected or C dogs can only be safely bred to a normal dog (A’s), as any other mating will produce significant numbers of affected progeny.

The most important point of using this type of DNA test correctly is that one can avoid producing any affected animals provided you know the DNA status of the parents for that disease.
Once all dogs in your kennel are clear or normal for the condition, no further testing is needed, provided you keep using normal animals

 

There is also some investigation into the way the hairless gene expresses itself

SCIENTIFIC RESEARCH ON THE INHERITANCE OF HAIR OF THE CHINESE CRESTED

from their website

The aim of this study is to obtain more insight on the inheritance of hair of Chinese Crested dogs. Because almost everyone has a preference for a particular hair type e.g., true or hairy hairless, it is useful to investigate which type of parents will bring forth a certain hair type in their offspring. To date one study has been done in which DNA (FOXI3) was examined. This revealed the difference between DNA of hairless dogs and powderpuffs but did not take the degree of hairiness into account. This study does take the degree of hairiness into account.

Therefore it allows predicting the hair type of puppies based on visible hair characteristics of the parenting dogs.

You as breeder of Chinese Cresteds can provide us with useful information. The more breeders respond the more reliable the predictions will be.

This study is also helpful for further investigation of DNA of Chinese Crested dogs.

 

 

 

Chinese Crested Breed Registry