What does MyDogDNA reveal about Bernese Mountain Dog and other Swiss Mountain and Cattle Dog breeds?

Bernese Mountain Dog is a breed of Swiss origin and the most popular breed among the Swiss Mountain and Cattle Dogs. The population has spread around the world and therefore different lines can presumably be identified. Nevertheless, all individuals of this breed have their origins in Switzerland. How does this show in the breed’s genetic diversity?

During the Fall and Winter of 2013-2014, breeders and enthusiasts of Bernese Mountain Dogs (BMDs) set out to actively explore the genetic diversity and relationships state of the breed with MyDogDNA. The results reported below are based on the 58 BMDs that had been analyzed by the end of March 2014. The majority of the dogs (42) were from Finland, while Russian dogs represented another significant group (14). In addition, the breed-group level plots include also the analyzed dogs of other Swiss Mountain and Cattle Dog breeds: ten Greater Swiss Mountain Dogs, seven Entlebucher Mountain Dogs and three Appenzell Cattle Dogs.

Genetic diversity state of the Bernese Mountain Dog population

The figure below offers a view to the genetic diversity level of Swiss Mountain and Cattle Dogs in comparison to the other dogs in the MyDogDNA database. These figures are also available online at www.mydogdna.com/breeds, and they will be updated in real time with each additional tested dog. The current median for genetic diversity of the Bernese Mountain Dog breed (blue line) is 24.7 % (range 22.4 % - 26.9 %). As seen in figure 1, this is lower than the median diversity level among all dogs in the MyDogDNA database (orange line), 28.8 % (range for all dogs 15.3 % - 40.1 %). No significant difference in diversity level was observed between Finnish and Russian BMDs.

Figure 1

Figure 1

Figure 1 also features a line (green) illustrating the joint diversity distribution of the analyzed Swiss Mountain and Cattle Dog group as a whole. This curve further confirms the diversity of the group as lower than the average observed across all breeds. The calculated diversity values of the breeds are summarized below. Please note that the values presented for other breeds besides BMDs are still based on a very limited number of dogs.

Table 1

Genetic relationships in Bernese Mountain Dogs

The genetic structure of a breed can be visualized graphically as demonstrated in the figure 2. The figure illustrates the genetic similarities and differences between individuals: dogs that are situated close to one another have similar genomes while dogs situated apart are genetically different from one another. Such visualization can be used to identify possible different breeding lines within the population. It also helps to evaluate which dogs could be mated to preserve the genetic diversity within the line as well as within the entire breed. In figure 2, dogs from Russia have been colored red while the remaining dogs in blue almost exclusively represent Finnish dogs. Although the Russian dogs tend to cluster together, there is clearly overlap between the genetic identity of the Finnish and Russian populations. This may be due to the fact that all individuals have their ancestral history in the same geographical area. Figure 3 includes all Swiss Mountain and Cattle Dogs and reveals distinct genetic identities for each of the four analyzed breeds.

FIgure 2

Figure 3

The genetic relationships analysis of BMDs revealed some potential clusters that could represent lineages of different breeders. With the current sample size, these genetic differences stand out more clearly than geographic differences between Finnish and Russian dogs. As more dogs get tested in the future, a better view to potential geographic and lineage differences will emerge. Overall, understanding of the genetic differences present between dogs in a homogeneous breed will aid in future identification of optimal breeding partners (i.e. the breeding pairs that will result in offspring that is as genetically diverse as possible).

For this purpose, the MyDogDNA service includes a custom-developed tool called MyDogDNA Breeder™. This tool uses the genetic data to identify breeding partners that are different from the user’s own dog, and does not carry the same inherited diseases based on the single gene disorder tests that are included in the MyDogDNA test panel. In brief, the Breeder tool ranks potential partners according to the expected genetic health and diversity of the offspring. It also displays where the identified partners are located geographically, and offers a direct means to contact the owners of the partners of interest through the MyDogDNA database. By the date of publication of this report, the breeder tool has been adopted for 73% of the tested Swiss Mountain and Cattle Dogs, which makes it a promising supportive tool for future efforts to increase the breed’s genetic diversity.

Tested genetic disorders

In addition to diversity testing, the MyDogDNA test panel includes screening for approximately 100 mutations known to underlie genetic disorders. In the analyzed Swiss Mountain and Cattle Dog group, carriers were discovered among Greater Swiss Mountain Dogs for a known bleeding disorder in the breed (trombopathia due to a defect in the P2Y12 receptor gene). The mutation underlying the P2Y12 defect was discovered in an extended pedigree of Greater Swiss Mountain Dogs in 2011, but predicted to be fairly widespread in the breed (Boudreaux et al. 2011, Vet Clin Pathol 40:202-206). Our findings support this prediction in that 80 % (8 out of 10) of the analyzed Greater Swiss Mountain Dogs carry the P2Y12 defect. The high carrier frequency could be a result of a strong genetic bottleneck caused by the re-establishment of the breed in the early 1900s, in combination with the relative harmlessness of the condition. The bleeding disorder caused by P2Y12 deficiency will likely go completely unnoticed in genetically affected individuals unless the dog undergoes surgery, is exposed to trauma, or is treated with blood platelet inhibitors (Boudreaux et al., 2011). Dog owners should nevertheless be aware of the condition for the best possible care in case of said situations. Due to the high carrier frequency of the condition, breeders are not advised to eliminate carriers from breeding. The frequency of the mutation in the population can only be decreased by “carrier” x “genetically healthy” - matings over the course of several generations and a long time period.

Summary

This genetic diversity assessment of Swiss Mountain and Cattle Dogs suggests that as a group, the analyzed breeds are somewhat less genetically diverse than dog breeds on average. We encourage breeders and breed enthusiasts to continue the exploration of the situation by expansion of the sample size, and its extension to include dogs from other countries as well. The real-time updated MyDogDNA database will continue to be a future source providing the most accurate view of the diversity state, and any progress made in maintaining and expanding genetic diversity.

In particular, we encourage more Greater Swiss Mountain Dogs, Entlebucher Mountain Dogs, and Appenzell Cattle Dogs to be analyzed. Our preliminary results from these breeds suggest that their diversity state is on a level even lower than that of BMDs. This calls for a more thorough exploration of the state, and efforts to strive towards increased genetic diversity in order to avoid effects of inbreeding depression. For the first time, modern bioinformatics tools can also be utilized to aid in identification of truly genetically different individuals and the selection of optimal matings for sustainable breeding that increases genetic diversity. The MyDogDNA Breeder™ matchmaking tool is expected to be an excellent supportive tool for these efforts also in Swiss Mountain and Cattle Dogs.

Finally, our exploration of known mutations underlying inherited disorders revealed high frequency of a bleeding disorder (trombopathia due to P2Y12 defect) in Greater Swiss Mountain Dogs. Dog owners and breeders should be aware of this condition as an explanation for excessive and prolonged bleeding observed e.g. during surgery or trauma. A gene test for the condition is available as a part of the MyDogDNA service.