Health tested !?!

Everywhere you read that dogs used for breeding should be health tested. Breeders advertise their puppies with parents that are health tested. For many people interested in puppies, this is sufficient information and they trust that the breeder knows his trade and has certainly done everything possible to breed healthy dogs. But unfortunately that is often not the case.

What is a health test?

Any veterinarian can assess the current condition of a dog. This is usually done at every vet visit. But that's not nearly enough for a breeding dog. Because in addition to the current physical condition, which can be determined during a visit to the vet, there is much that cannot be determined in this way.

X-rays for hip and elbow dysplasia are required by many breed clubs for most breeds. The evaluation procedures and evaluation systems are different in some countries and I have described them before. Every breeding dog should also be x-rayed for hemivertebra, but this is not mandatory in most countries.

A lot has happened in this area since the first molecular genetic test for dog breeders became available about 25 years ago and today we have an almost confusing number of different genetic tests that could help us to make responsible breeding decisions. But not all genetic tests are the same. And when a breeder tells their prospective customer that the puppy's parents are genetically tested and healthy, then the prospective buyer trusts the breeder again, because DNA doesn't lie. Does it?

What is a genetic test?

There is not one gene test that is the silver bullet in dog breeding to avoid hereditary defects. In addition to various tests applicable to all breeds, there are a large number of tests that are breed specific and test for special traits found only in that breed.

There are also specific, as well as general, not unimportant genetic testing options for the Shar Pei. I would like to present the most important of these general and specific tests, especially with regard to how to understand the results. Because a well-informed prospective buyer can get a better picture of the parents of their dream puppy. And when we see how many Shar-Pei today suffer from various diseases typical of the breed, allergies and food intolerances, then it is worth doing some research.

Breed specific tests:

SPAID Test

There are two different tests. One was developed in Sweden, the other in Germany. Both genetic tests test for different mutations on chromosome 13 that are related to SPAID.

The SPAID test from Sweden is also often called the CNV test. It is tested for a mutation of a regulatory gene of HAS2. A tested dog is either clear (CNV2), single carrier (CNV6), or double carrier (CNV10). This means:

  • CNV2 - The dog does not carry the trait and is therefore not at increased risk of the disease
  • CNV6 - The dog is a single carrier of the trait and is four times more likely to develop SPAID than a dog without the trait (CNV2). It is important to know that if both parents are single carriers, their puppies have a 25% chance of being double carriers.
  • CNV10 - The dog is a double carrier of the trait and is eight times more likely to develop SPAID than a trait-free (CNV2) dog.

The SPAID test from Germany tests for a missense mutation in the MTBP gene, which causes an important protein in affected dogs to malfunction in the inflammatory metabolism. A tested dog is either N/N, N/Spaid or SPAID/SPAID

  • N/N - The dog is homozygous
  • N/SPAID - The dog is a heterozygous carrier
  • SPAID/SPAID - The dog is a homozygous carrier
Hunde
Inheritance of traits

In the case of heterozygous and homozygous carriers, there is a probability that the dogs will develop SPAID in the course of their lives. This probability is just as high in homozygous carriers as in dogs tested for CNV10 with the Swedish test.

SPAID, often simply called "SharPei fever", is probably the health disorder most often mentioned and feared in the Shar Pei world. This is an auto-inflammatory disease, comparable to the Familial Mediterranean Fever known in humans, which occurs in about 23% of western Shar Peis. And 23% means every fourth dog. This is probably the most important reason why every dog that is bred not only has to be tested (for both mutations), far-reaching breeding consequences must also be drawn. Because every dog that is not homozygous , not carrying the trait, can develop SPAID in its lifetime, which not only means great suffering for the dog, but also for its owner.

Another important point, why we have to take the topic very seriously and need radical changes in breeding is the following. We know of approximately 23% of the worldwide Shar-Pei population who will suffer from SPAID in their lifetime, thus being diseased carriers. We also know that not every carrier will get sick. In genetics there are certain formulas that can be used to calculate the proportion of carriers in the entire population. According to these calculations, it are almost 60% of the entire Shar Pei population carriers, single or double. This means that just 17% of the worldwide Shar Pei population do not carry this trait and are therefore genetically healthy with regard to SPAID. I hope everyone is beginning to realize how shocking these numbers are.

More information about SPAID

Every puppy buyer should be aware of the risk he is running when he buys a puppy that is not homozygous. On the one hand for the dog concerned, but also for the reason that breeding with carriers will continue as long as there is demand for puppies that are carriers. Because unfortunately it's not us breeders who breed according to modern population genetic knowledge. Unfortunately, external pressure will be needed to get rid of outdated breeding ideas and allow us to breed exclusively homozygous dogs using modern methods.

POAG/Pll Test

Primary open-angle glaucoma (POAG) is a connective tissue disorder in the eye that is often genetic. This means that the water in the eye chamber cannot drain properly. The resulting increase in internal pressure in the eye puts a strain on the optic nerve and the retina, is very painful for the dog and can ultimately lead to blindness. The connective tissue disorder often also causes a dislocation of the lens (Pll) in the eye.

Similar to the CNV SPAID test, this test looks at whether the tested dog trait-free, a single or double carrier.

General molecular genetic tests

Genetic diversity

By genetic diversity we mean the presence of differing genetic information in individuals of the same species, in our case the worldwide Shar Pei population. Genetic diversity is the prerequisite for the ability to adapt to changing habitat conditions, environmental influences or diseases. It is therefore essential for the survival of individual populations.

Insufficient genetic diversity is probably the biggest problem in modern pedigree dog breeding. In modern pedigree dog breeding we have closed populations, which means that only dogs from the same population are allowed to breed with. In modern sport horse breeding, stallions from other breeds are also used as required, this is called an open population. The difference is obvious, the genetic diversity in sport horses is much higher than that in purebred dogs. Only those genes are available to each breed that were present in the breed since the stud books were closed, i.e. only dogs of the same breed were bred with. No new genetic material is added, but some is lost with each generation, since breeding does not continue with every puppy in a litter.

With the Shar Pei, as with most other breeds, the low genetic variance is also due to the fact that the population has been severely decimated by external influences, leading to a genetic bottleneck situation. This is when modern Shar Pei breed breeding began. The genetic diversity of the Western Shar-Pei that exist today descends from very few dogs and continues to decline with each generation. Another aspect that leads to the fact that genetic diversity continues to decrease and defective genes (known or unknown) have the opportunity to spread disproportionately in the population is the "Popular Sire Syndrome", which I will not address at this point into more depth.

In the following I would like to present a few of the most important molecular genetic tests and explain their importance.

Genomic Coefficient of Inbreeding (gCOI)

The higher the level of inbreeding in a population, the lower the level of genetic diversity, since more identical alleles are passed on than different alleles. So far, the coefficient of inbreeding (COI) has been calculated using classic pedigrees. However, the accuracy of these calculations has disadvantages, for example incomplete or incorrect pedigrees.

The genomic coefficient of inbreeding can now be determined by some laboratories. As with the classic calculation based on the pedigree, you must also pay attention to how many generations were taken into account in the calculation, since the value changes with each additional generation taken into account. Only values with an identical number of generations can be compared with each other.

Diting
Example: Diding's gCOI compared to all breeds

Modern laboratories are able to calculate this gCOI over 3, 6, 12, 25 or 50 generations. Specific areas in the dog's DNA are used for the calculation. The length of these ranges is related to the number of generations considered when calculating the genomic inbreeding coefficient.

The average gCOI of all breeds is 25%, according to a recently published international study. UCDavis has published an easily understandable summary of this study on its website. One must keep in mind that most dog breeds exhibit such a high level of inbreeding, well beyond what is considered safe for human or wild animal populations.

So having the gCOI of breeding dogs determined is a logical and very important step for detailed population and diversity management in our breed. Because we don't only breed for ourselves with our dogs. Each mating will have an impact on future generations. We are therefore responsible for an entire population.

Heterozygosity

Diting
Example: Diting's heterozygosity value compared to all breeds

Heterozygosity indicates the percentage of different genetic markers inherited from a dog's parents. Homozygous means that both alleles of a gene are the same. Heterozygous means that both alleles of a gene are different. Thus, for high genetic diversity, a high percentage of heterozygosity is desirable. Today, this percentage can be easily determined using molecular genetics by comparing many thousands of markers from the tested dog to determine whether they are homozygous or heterozygous. The result then represents the percentage of desired heterozygosity.

The average heterozygosity value of all breeds is about 33%. A high percentage of heterozygosity is therefore desirable for genetic diversity in a breed.

DLA haplotypes

The DLA (Dog Leukocyte Antigen) are a group of genes from the area of the MHC genes. These genes encode proteins that are responsible for the immune system. Both the functionality and disorders of the immune system depend on the MHC. These disorders are expressed in autoimmune diseases, which means that one's own cells are interpreted as foreign and attacked.

There are three different classes of MHC genes that have different functions. The class II genes, which include DRB1, DQA1 and DQB1 (DLA), act in the early important phase of the immune system response. Due to the large variety of invading foreign bodies, such as viruses or bacteria, the presence of different alleles, i.e. different copies of the same gene, is all the more important.

DLA
Possible results from mating different haplotypes

The area of the MHC genes in dogs is now quite well researched. About 190 alleles of the group II genes (DRB1, DQA1 and DQB1) are known to date. In group I we now know 51 alleles in the dog. A combination of three alleles, the DLA haplotypes, is always inherited. Over 350 of these haplotypes have been found in dogs to date.

That sounds like a lot and you might think that this genetic aspect is quite diverse in our dogs. Unfortunately, exactly the opposite is the case. Because if you look at the individual breeds, you can see how few of these haplotypes are still present in these closed populations today. Most dog breeds whose DLA haplotypes have been examined more closely today only have an average of 8-10 different haplotypes. Since the DLA haplotypes have only been determined for a few Shar-Pei to date, we cannot make any statements about the condition of our breed in this area.

DLA
Possible results from mating identical haplotypes

So to give us an idea of the Shar Pei's DLA haplotype situation, it would be highly recommended that breeders have their dogs tested for this. Because this area can also help every breeder to make wise breeding decisions. Through virtual test matings one can see what the expected distribution of haplotypes would be in the puppies. Recommend are matings where the parents do not have identical haplotypes.

In many dog breeds, clear connections have been found between different haplotypes and certain breed-typical diseases. Another reason why breeders should have their dogs tested, as this way we can prevent further damage to the breed.

Genomic breeding value estimation

Genomic breeding value estimation is already widespread in livestock farming, but is still new in pedigree dog breeding. In this way, a dog's breeding value can be assessed on the basis of SNP haplotypes if these are associated with defined traits. In order to determine this breeding value, however, sufficient data must first be available for a breed in order to be able to draw genetic conclusions.

The example of the Bernese Mountain Dog, in which the genomic breeding value in terms of longevity, hip dysplasia and elbow dysplasia has been estimated for some time, shows the advantage this option offers us breeder.

Especially if you want to keep a puppy from your own litter for further breeding plans, then selecting the best puppy for breeding based on the genomic breeding value would be even easier to determine. Especially when you add in the breed-specific and general molecular genetic test results described above.

Hopes

Even if the last test presented only helps breeders to make better breeding decisions, I hope that my presentation and explanation of the general and breed-specific molecular genetic testing options is easy to understand and will help future puppy owners to be able to make their breeder and puppy selection easier, because everyone wants a healthy dog.