Bitten Jönsson - Jotunheim kennel - Δανία
 Συγγραφέας, Sonia García

Denmark

http://www.dobermann-pedigree-database.co.uk/?p=266

soniagarciaherdez@gmail.com
 

Understanding the prevalence of DCM in Dobermann. Some reflections

The results of the work of Wess et al. 2010, have enabled us to confront a crude reality, approximately 60% of European Dobermann population will die of DCM. Article of Dr. Reinhard Haberzettl, old Breed Warden for the East German Dobermann Verein, published in ”Das Schäferhund Magazin” Nr.6 Juni 2006, where he include two interesting data of prevalence of DCM for year 1989 (26.1%) and for year 2004 (46.3%) which provides new data about the historical evolution of the prevalence of DCM in the Dobermann European population. When we represent all data from two sources, a good correlation is shown which illustrate that Haberzettl data are valid.

This supposes that with actual mating system spread rate of DCM is about 1.5% by year and in 2020 the prevalence will be 72%!

In words of Dr. Reinhard Haberzettl (2002) : “The Doberman was created from mixtures of various breeds and half-breeds at the end of the 19th century. This genetic variety was a great health advantage. Up to approximately 1950, there were practically no hereditary health problems, worldwide. These qualities still remained in the populations of East Germany and Eastern Europe up to the nineties”.

An approximate lineal increase of prevalence over time leads to a quadratic increase in the number of affected during the initial spread of the DCM in the population between 1970-1988 and a more moderated increase trend (almost lineal) from 1989 to actual (figure 2). Simulations shown that, under a realistic scenario of 40 popular sires regarding the imbalance in the use of sires, the dissemination of the risk was indeed 4.4 times higher than under random mating conditions (Leroy. and Baumung, 2010). Parallel evolution of fraction of popular sire’s offspring (sires with more than 100 pups sired) and DCM affected dogs (figure 2) shows that initial critical spread of the DCM during period 1970-1988 coincides with the period of popularization of the breed and the overuse of popular dogs. After this period offspring of popular sires is less accentuated and also the increase of number of affected dogs.

Leroy. and Baumung, 2010 noted that linebreeding practice outside popular sire use not increase the risk to dissemination of genetic diseases. However mating trends in population of European Dobermann illustrate that inbreeding rate is based on popular sire practice as shows the good correlation between the average inbreeding coefficient (COI of seven generation pedigree) in the population and the fraction of population sided by popular sires (figure 3).

Often we engage in lengthy discussions about the genes involved in the transmission of DCM in the Dobermann. However we continue to be unscrupulous in the choice of parents and the obvious risk posed by the use of high-risk parents is ignored in favor of the future success of offspring in the conformation show-rings. In the next graphic (figure 4)  is show the incidence of DCM in offspring of some popular sires over time in the critical period of increase of DCM number of affected dogs. We can observe the same quadratic tendency observed in figure 2, and as that majority of popular sires in this period are DCM affected or at least with one affected progenitor.

Breeding rules imposes by Doberman breed clubs and National Kennel clubs are paradox in some ends.

Unbalance between number of reproductive males and females produces low flow of male genes which exacerbate genetic drift by decrease of effective population size and loss of genetic diversity. Last researches have demonstrated that the popular sire phenomenon is the most problematic breeding practice, since it has also led to the dissemination of a large number of inherited defects. The practice should be limited by taking measures such as restricting the number of litters (or offspring) per breeding animal (Leroy, 2011).

The selection in Doberman breed using restraint rules, as the ZTP, favors the offspring of some individuals, which undoubtedly accentuated the phenomenon of genetic drift and reduce diversity. In figure 4b shows the evolution number of reproductive females per reproductive male in the population of European Dobermann over generations. We can observe that number of reproductive female by reproductive male increase over generations and only few males are selected as breeding animals and genes of rest of males are purged of the population gene pool. Otherwise, although selected males for breeding were healthy, this phenomenon favors the concentration of deleterious genes as homozygous.

Limitation of endogamy in mating has been proposed by Danish Kennel  Club and inbreeding  coefficients  of  up  to  6.25%,  equivalent  to  first  cousin  mating,  are accepted. In effect, in figure 6 we can see that COI of litters born 2009 on seven generation pedigree shows a positive biased distribution (not normal) which shows that endogamy is a dominant practice in mating. In the figure 6 is shown the frequency distribution of COI from historic data of 3998 litters in the period 1970-2009, and for a sample of 129 litters of most recent population born 2009, illustrate that inbreeding is a dominant practice in mating in both cases and frequencies distribution of COI is positive biased (positive skewness of not normal distribution) (Historic sample: Skewness =+1.233; Actual sample: Skewness= +0.926).

However some rules are adopted to limit the number of litters or offspring per breeding animal by Danish Kennel Club, like 4 to 5 litter max per female, and 27 offspring per male over a specific period of time. The Fédération  Cynologique  Internationale  (FCI)  recently  recommended that, within a breed, no dog should have more offspring than 5% of the number of puppies registered in the breed population over a 5-year period. For a breed with a low number of inscriptions (1,000 inscriptions/year; maximum 50 pups/sire on 5 years) this recommendation can be adequate, but clearly ineffective for a popular breed as Dobermann (10,000 inscriptions/year; maximum 2,500 pups/sire on 5 years).

Observation of population structure of most recent population born 2009 can illustrate a new paradox. On a sample of European population born 2009 I have found three significant clusters and two functional groups. Main group (79.5% litters) include conformation dogs and/or ZTP related with two popular sires: Cluster 1 include dogs of majority related with Graaf Quirinus v. Neerlands Stam (GQvNS), and less with Prinz v. Norden Stamm (PvNS), Cluster 2  include dogs of related in the same extension with Graaf Quirinus v. Neerlands Stam, and Prinz v. Norden Stamm. Cluster 3 minority group (20.5% litters) includes pure working dogs related with Bingo v. Ellendonk (BvE) and much lesser with Graaf Quirinus v. Neerlands Stam, and Prinz v. Norden Stamm (figure 5). Good conformation is the first breeding goal for breeders and line-breeding and close-breeding based on pedigree data is a cultural practice of mating system common in professional and regular breeders who register several litters per year (Leroy et al. 2007). Clusters size of population born 2009 confirms that conformation is the goal of majority of breeders, and population structure illustrates the “fetish power” of pedigree.

No significant difference in a Student t-test is observed in average COI between groups (Sig. two tailed = 0.257). Application of Danish Kennel Club policy implicates that dogs of Cluster 3 (minority) must be mating with dogs of Cluster 1 or 2 and low available diversity can be loss to conform a homogeneous group. However dogs related with Bingo v. Ellendonk (Cluster 3) shows higher fitness (average litter size-ALS) than dogs of two others clusters and significant differences in a Student t-test have been observed (Sig. two tailed = 0.001). (table 1) which illustrate that selection for utility (working) is an advantage in terms of genetic fitness over the selection for anatomical traits (conformation).

Recessive deleterious mutations are purged more easily by selection in small or inbred populations than in populations with random mating (Charlesworth and Charlesworth, 1999). This positive effect on fitness traits occur faster under close breeding (Leroy and Baumung, 2011). It’s possible that this phenomenon of purging of recessive deleterious mutations linked to inbreeding affects positively fitness of this cluster 3.

Likewise, this genetic advantage of dogs related with Bingo v. Ellendonk, despite the high average COI of this group (10.55%), may be lost when dogs of Cluster 3 are mating with dogs of Cluster 1 or 2, which illustrate that general rule as to limit the COI of mating, it is unfavorable in this case.

The conclusions of the analysis of population structure and fitness for the population born 2009, suggests the possibility that average life span may differentially affect dogs of both functional groups (working dogs related with Bingo v. Ellendong and show-dogs related with Graaf Quirinus v. Neerlands Stam, and/or Prinz v. Norden Stamm. The inability to perform the analysis of average life span on the same sample of dogs born in 2009, determines that I did a statistical analysis on a separate sample including 281 records of dogs born between 1990 and 2008 belonging to both groups (231 show dogs/50 working dogs). Each record includes: name of the dog, dates of birth and death, life span (LS), bloodline group pedigree (Working dogs or Show dogs), and inbreeding coefficient COI.

 Difference in a Student t-test for average COI between groups of this sample (Sig. two tailed = 0.044) is in the limit of significance at 0.05 level, but is higher for BvE related dogs (Average COI=12.54%) than for GQvNS and/or PvNS group (Average COI=10.41%).

Comparison of Kaplan-Meier survival curves (figure 6) for dogs related with both groups show that difference between groups is significant (Mantel-Cox log rank Chi-square=12.685; Sig.=0.000), and from an early age the survival factor is lower for show-dogs group in all age classes. Average life expectancy is +1.437 years higher for BvE related dogs (Average LS=8.08 years) than for GQvNS and/or PvNS group (Average LS=6.64 years). For long lived dogs belonging to age classes with LS>10 years, difference is also evident between groups: Cum. Survival =16.5% for BvE related dogs, and Cum. Survival =6.3% for GQvNS and/or PvNS group.

Analysis of variance from bivariate correlations for litter size where dog is born, COI of litter and life span variables within groups not shows significant correlations in both cases.

 It’s clear that both genetic advantages on fitness and life expectancy of dogs related with Bingo v. Ellendong are linked to accomplish both simultaneous conditions: dogs strong related by kinship with Bingo v. Ellendong and selected for working. Also becomes clear again that the limitation of COI of matings, is a criterion which may be disadvantageous in certain cases

 The statistics of long-lived dogs are fine as curious cases but we can not extend to broad families except in very rare cases when the proportion of long-lived dogs is statistically significant and extensive to a high percentage of entire lineage.

 We must not forget that long lived dogs from non healthy lineages can produce high proportions of non healthy dogs because are carriers of deleterious genes. Even proportions of affected dogs by genetic diseases, as DCM, on the offspring can be higher for a long lived sire than for short lived sire. Transmission of genetic diseases depends of genes provided by both sire and dam sides, but for popular sires with a higher number of offspring can be considered independent of dam input because diverse dam are implicated in the statistical of offspring.  Curiously the comparison of incidence of DCM in the offspring of two contemporary popular sires:  Eick v.d.. Rappenau (1987-1994, dead by DCM) (incidence of DCM in the offspring=7.5%) and Prinz v. Norden Stamm (1988-2001- a long lived dog) (incidence of DCM in the offspring=10.4%) which illustrates that life span is only one variable in complex equation of survival.

Prof. Sonia Garcia, PhD

Bibliography

Charlesworth B., Charlesworth D..(1999). The genetic basis of inbreeding depression. Genet. Res. Camb. 74:329-340.

Haberzettl R (2002). Wachsende erbliche Gesundheitsprobleme in der Rassehundezucht am Beispiel des Dobermanns in Deutschland, in Europa und in den USA – eine vergleichende Übersicht. Das Schäferhund Magazin” Nr.4 August 2002 (English traduction by L. Kurz-United Dobermann Club)

Leroy G. , Verrier E. , Wisner-Bourgeois C , Rognon X (2007). Breeding goals and breeding practices of French dog breeders: results from a large survey. Revue Méd. Vét., 158(10), 496-503.

Leroy G. and Baumung R. (2010) Mating practices and the dissemination of genetic disorders in domestic animals, based on the example of dog breeding Anim. Genet. 2010, Journal compilation. Stichting International Foundation for Animal Genetics.

Leroy G. (2011). Genetic diversity, inbreeding and breeding practices in dogs: Results from pedigree analyses. Vet J.; 189(2):177-82.

Wess G, Schulze A, Butz V, Simak J, Killich M, Keller LJ, Maeurer J, Hartmann K (2010): Prevalence of dilated cardiomyopathy in doberman pinschers in various age groups. J Vet Intern Med.; 24(3):533-538.