Introduction

In Sweden there are about 950 000 dogs, 85% of which are purebred and registered in the Swedish Kennel Club (SKC). Furthermore, a large proportion of Swedish dogs have a health insurance. Thanks to the extensive registration and insurance of dogs in Sweden, large amounts of data regarding morbidity, mortality, and ancestral background are being collected and made available to breeders and scientists. These databases are valuable tools for breeders and breed clubs in selection of breeding stock and in breeding planning. They also offer unique possibilities for both epidemiological and genetic studies on different diseases in dogs.

Genetic Health Programmes

The SKC started to develop genetic health programmes more than 25 years ago. Records from these programmes are stored in the SKC database and are freely accessible through the SKC web site. The first programmes concerned hip and elbow dysplasia (HD and ED). Today, numerous breeds are included in a genetic health programme for HD or ED, implying that hip or elbow status of both the sire and the dam should be known for the offspring to be registered in the SKC. In many breeds, an additional requirement is that dogs should be free from HD to be accepted for breeding.

In addition to HD and ED, genetic health programmes for other inherited conditions, such as hereditary eye diseases, have been developed. These are based on breed-specific needs and have been introduced on request from the breed clubs.

Besides physical health, the SKC has developed programmes with respect to mental health and management of genetic variation. Since 2002, all breeds belonging to the Swedish Working Dog Association are obliged to undergo a standardised behavioural test (dog mentality assessment), describing the mental status of the dog, before being used in breeding. Furthermore, Border Collies need to undergo a working test for evaluation of their herding skills if the progeny are to be registered in the SKC.

Management of genetic variation is important to avoid loss of genetic diversity, manifestation of recessive defects and inbreeding depression. In some Swedish breeds, limitations for the maximum number of offspring allowed for a single male have been introduced to avoid extensive use of popular sires. Also, programmes for out-crossing with individuals from closely related breeds have been developed in order to increase the effective population size and improve health traits.

In conclusion, the genetic health programmes currently operated by the SKC aim at improved physical and mental health, as well as maintained possibilities for a sustainable breeding with respect to genetic variation. However, so far genetic health programmes for physical health have been developed only for diseases with well defined and validated methods for examination and diagnosis. Many breeds have other, less well defined, inherited conditions that may have a larger impact on the dogs' health. It is therefore important not to put too much focus on one or a few diseases only because they are easy to diagnose and to record. Because genetic health programmes only cover some aspects of mentality and functionality, most breed clubs have additional recommendations or restrictions in their breeding policies.

New Tools

Development of Breeding Strategies

Breeding of dogs is regulated both on international and national levels. In addition to breed specific genetic health programmes, all members of the SKC are obliged to follow the general regulations and breeding policy set up by the SKC. These documents give general restrictions, guidelines, and goals for breeding of dogs. However, there are almost 300 different breeds in Sweden and each breed has its own specific conditions that are important to consider in the breeding programme. Therefore, in 2001 the SKC decided that each breed should have their own breeding strategy, taking into account all aspects relevant in the breeding goal for that specific breed. Thus, the breeding strategy should consider and prioritize between aspects of both physical and mental health, also taking the population structure and genetic variation into account. Breed-specific goals and strategies to achieve these goals should be included, constituting an overall plan for the breed. The responsibility for developing these strategies was given to the breed clubs, and at present more than 140 clubs have submitted a breeding strategy to the SKC.

Breeding Value Prediction

Despite efforts to reduce the frequency of HD and ED by means of genetic health programmes, based on radiographic examination of the phenotype and subsequent mass selection, the improvement has been disappointing in several breeds. Low or no improvement in HD has been reported also by other countries (Lingaas and Heim, 1987; Willis, 1997; Leppänen and Saloniemi, 1999).

In grading systems for HD and ED there are limited possibilities for measuring differences among phenotypically normal dogs. In some breeds, a large proportion of the dogs are free from dysplasia which makes selection based on the phenotypic value alone inefficient. In addition, the phenotype is affected by various systematic environmental factors, e.g., age at screening (Distl et al., 1991; Swenson et al., 1997a, b; Mäki et al., 2000). Also the type of chemical restraint, used for sedation during radiographic examination of HD, has an impact on the diagnosis of hip status (Malm et al., 2006a). The effect of different environmental factors on evaluation of hip and elbow status implies that the individual's own screening result alone may be inaccurate for selection purposes.

Genetic evaluation using mixed linear models (often called BLUP) for prediction of breeding values have been used extensively in breeding of cattle, horses, poultry and swine for several years. However, in dog breeding this methodology has been used only to a limited extent. Prediction of breeding values for HD and ED would enable a more accurate comparison of genetic merit of dogs. The BLUP method makes use of all available information about relatives and simultaneously adjusts for environmental effects. Selection against HD and ED based on predicted breeding values has already been introduced in some countries, e.g., Finland and Germany. In Sweden, the SKC is planning to implement breeding value prediction for HD and ED as a routine for a number of breeds during 2007.

A genetic study of HD and ED has been conducted in two breeds, Rottweiler and Bernese Mountain Dog, to estimate the amount of genetic variation in HD and ED, and to assess genetic trends (Malm et al., 2006b). Based on these results, a statistical model for routine prediction of breeding values for HD and ED in Swedish dogs was suggested. The next step will be to evaluate the model also for other breeds.

The genetic evaluations of HD and ED in Sweden will be managed by the SKC and breeding values will most likely be updated once a week. Only dogs with an own screening record will get their breeding value published, together with the accuracy of the prediction.

A strategy for implementation of the breeding values in the overall breeding programme for each breed is needed. Other traits included the breeding strategy need to be considered relative to HD or ED. Besides, the relationship between individuals selected for breeding must be considered to avoid increased inbreeding due to selection of close relatives.

Breeding value prediction can be a useful tool for genetic evaluation of traits other than HD and ED. Genetic improvement not only of other diseases, but also behavioural and functional traits, could probably be enhanced by selection on breeding values instead of phenotypes.

DNA Tests for Canine Disorders

Advances in molecular genetic studies of the dog and the availability of the canine genome sequence imply that an increasing number of genes underlying diseases in dogs are being revealed. The development of DNA tests for different gene mutations makes it possible to accurately predict the genotype of an individual dog with respect to a specific disease, i.e., to identify genetically normal, carrier and affected animals. The possibility to identify carriers of a defective allele enables a more subtle management of breeding programmes to decrease the frequency of a particular disease gene without unnecessary reduction of the overall gene pool.

The SKC currently records results from DNA tests for canine leukocyte adhesion deficiency (CLAD) in the Irish Setter, congenital stationary night blindness (CSNB) in the Briard, von Willebrand disease in the Kooikerhondje and one type of progressive retinal atrophy (prcd-PRA) in a number of breeds. All results are published on the SKC web site for anyone to access and genetic health programmes based on the DNA testing are developed for each breed individually.

Internet Based Breeding Statistics

The SKC has recently developed an Internet based service including breeding statistics for both individual dogs and for each breed as a whole. The statistics are based on results from genetic health programmes, the dog mentality assessment, official competitions, and dog shows, as well as pedigree information. For individual dogs, own records as well as statistics for littermates, full-sibs and offspring are available. Also, the pedigree and coefficient of inbreeding is shown for each dog. The population-wide information for each breed includes statistics on number of registrations, health traits, mental status, breeding animals (regarding number of offspring and grandchildren per sire or dam, litter size, and age at breeding) and average levels of inbreeding by birth year. Furthermore, the service contains an option to calculate the expected inbreeding coefficient for offspring resulting from a planned mating.

This tool is available to anyone through the SKC web site and is very useful to breeders for genetic evaluation and selection of breeding animals. It also facilitates for breed clubs to assess the overall situation in the breed.

Conclusion

Dog breeding is of concern not only to individual breeders, but also to breed clubs, kennel clubs, geneticists, veterinarians, and authorities. Sustainable breeding of healthy dogs is facilitated by cooperation between the different parties and agreement about the breeding goals. In addition, genetic evaluation and selection must be based on accurate information about the individual animals and the breed as a whole. Recording of traits considered to be of importance is therefore essential, as well as pedigree information to enable evaluation of population structure and studies of the mode of inheritance for different traits. Consequently, the access to information and tools that enhance genetic evaluation is of great value. The development of breed-specific breeding strategies constitutes a solid basis for a comprehensive and long-term breeding programme.

References

1.  Distl, O., Grussler, W., Schwarz, J., Krausslich, H., 1991. Analysis of Environmental and Genetic Influences on the Frequency of Hip Dysplasia in German Shepherd Dogs. J. Vet. Med. A. 38, 460-471.

2.  Leppänen, M., Saloniemi, H., 1999. Controlling canine hip dysplasia in Finland. Prev. Vet. Med. 42, 121-131.

3.  Lingaas, F., Heim, P., 1987. En genetisk undersøkelse av hofteleddsdysplasi i norske hunderaser [Genetic investigation on hip dysplasia in Norwegian dog breeds].Norsk Veterinærtidsskrift 99, 617-623.

4.  Malm, S., Danell, B., Audell, L., Strandberg, E., Swenson, L., Hedhammar, Å. 2006a. Impact of sedation method on the diagnosis of hip and elbow dysplasia in Swedish dogs. Prev. Vet. Med. Submitted.

5.  Malm, S., Strandberg, E., Fikse, W.F., Danell, B., 2006b. Genetic Variation in Hip and Elbow Dysplasia in Swedish Rottweiler and Bernese Mountain Dog. In preparation.

6.  Mäki, K., Liinamo, A.E., Ojala, M., 2000. Estimates of genetic parameters for hip and elbow dysplasia in Finish Rottweilers. J. Anim. Sci. 78, 1141-1148.

7.  Swenson, L., Audell, L., Hedhammar, Å. 1997a. Prevalence and inheritance of and selection for elbow arthrosis in Bernese Mountain Dogs and Rottweilers in Sweden and benefit:cost analysis of a screening and control program. J. Am. Vet. Med. Assoc. 210, 215-221.

8.  Swenson, L., Audell, L., Hedhammar, Å. 1997b. Prevalence and inheritance of and selection for hip dysplasia in seven breeds of dogs in Sweden and benefit:cost analysis of a screening and control program. J. Am. Vet. Med. Assoc. 210, 207-214.

9.  Willis, M.B., 1997. A review of the progress in canine hip dysplasia control in Britain. J. Am. Vet. Med. Assoc. 210, 1480-1482.