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The Welfare of Pedigree Dogs
By Albert T Sang
Introduction
Since Victorian times, the breeding of pedigree dogs has been performed under a closed
studbook system, which allows only descendants from an initial population of animals to
breed (McGreevy, 2008). This system inevitably increases the risk of inherited disorders and
jeopardises the health and welfare of many animals (McGreevy, 2008). This paper reviews
recent literature investigating genetic diversity and the incidence of inbreeding in purebred
dogs as well as exploring the consequences of these breeding practices on the welfare of
animals.
Discussion
Inbreeding and loss of genetic diversity in any animal is known to cause an increase in the
prevalence of genetic disorders (Nicholas, 2003). A recent study by Calboli et al. (2008)
focused on investigating the population structure and incidence of inbreeding in purebred
dogs. By developing novel approaches for examining population structure and using
previously defined formulae for presenting inbreeding, Calboli et al. (2008) analysed the
electronic pedigrees of 10 breeds of dogs (2.1 million dogs in total) from the UK Kennel Club
database.
Extremely inbred dogs were identified in each breed and the effective population
size was estimated to be between 40 and 80 dogs for all but two breeds. Alarmingly, the
effective population size of these breeds was several orders of magnitude smaller than the
actual number of dogs registered in each breed. It was also discovered, in all but three
breeds, that greater than 90% of unique genetic variants are lost over six generations, which
indicates the dramatic effect that breeding patterns have on genetic diversity (Calboli et al.
2008). Although this was a large-scale study of many generations of pedigree dogs, it mainly
concentrated on the most popular breeds; the incidence of inbreeding and loss of genetic
diversity could be a lot higher in rarer breeds with smaller populations.
This study asserts a need for change in breeding practices to improve the health and welfare
of pedigree dogs. By opening studbooks and relaxing breed rules, controlled out-crossings
could be performed to enhance genetic variation within breeds (McGreevy, 2008; Calboli et al.,
2008).
In conforming to stringent breed standards, breeders have had to rely on inbreeding that has
resulted in loss of genetic variability and led to the high prevalence of recessive genetic
disorders. A study performed in Poland, based exclusively on the Polish hound (a rare breed
of scent hound originating from eastern Poland), also looked at genetic diversity through
analysis of pedigree records (Glazewska, 2008). Data from 247 litters born at 105 kennels
were evaluated to characterise the genetic variability of the breed and assess breeding
practices over a span of 44 years (1960-2004).
Through extensive analysis of the pedigree, the authors found that the breed originated from
only 19 founders, with only two individuals making a predominant contribution to the gene pool
(Glazewska, 2008).
This finding relates to the overuse of the “popular sire”, whereby, a small number of individuals
father most of the litters in a breed, due to their desirable traits (Calboli et al., 2008). The low
number of founders and the high disproportion of particular dogs in breeding use resulted in the
increasing incidence of inbreeding.
The inbreeding coefficient was higher than 25% in 69.25% of litters; with 20.2% of litters having
an inbreeding coefficient of 40%. The poor gene pool seems to be strictly connected to the
deteriorating health of the population, which draws into question the future of the breed (Glazewska,
2008).
It is paramount that breeders and regulators rationally and scientifically review breed standards to
improve welfare standards by removing any aspects or traits that could be contributing to welfare
problems (McGreevy & Nicholas, 1999; Higgins & Nicholas, 2008).
According to a study performed by Jensen et al. (2008), disk calcification at 2 years of age is
a significant indicator of clinical disk herniation in Dachshunds. This study, on the relationship
between intervertebral disk calcification and clinical disk herniation, included 61 animals that
had been scanned for calcification of the intervertebral disks at two years of age in previous
studies. Only 36 dogs had survived to the present day, with the age of all dogs being greater
than eight years.
Radiographic examination was performed on the surviving dogs, while information on the
occurrence of disk herniation between 2 and 8 years of age was obtained from owners via
questionnaires. Associations between the numbers of calcified disks and
clinical disk herniation were analysed with a maximum likelihood logistic regression. It was
found that the number of calcified disks at 2 years of age was a good predictor of clinical disk
herniation.
Furthermore, the risk of euthanasia following disk herniation was significantly
greater in dogs with >4 calcified disks (Jensen et al., 2008). Although this study was
performed on a small sample of dogs, it highlights the relationship between clinical disk
herniation and disk calcification, which is known to be a highly heritable trait within
Dachshunds (Jensen & Christensen, 2000). This study also emphasises the need for
surveillance of breeding populations of pedigree dogs, so that dogs can be screened before
their use within breeding programs. Furthermore, appropriate surveillance would allow
tracking of new disorders as they emerge (McGreevy, 2008).
Show judges have a large influence on the selection of dogs used in breeding; hence, they
have a profound impact on the health and welfare of purebred dogs. Educating judges in
proper functional anatomy is almost as vital as making them recognise their responsibility in
enhancing the health and welfare of pedigree dogs (Indrebo, 2008).
Conclusion
Veterinary associations, breeders and welfare charities must unite to create a new model for
dog-breeding practices that utilises the latest advances in genetics and epidemiology
(McGreevy, 2008). The goal of modern breeding should be based on a comprehensive
understanding of biology, so that all dogs are able to live long, happy and healthy lives
(McGreevy, 2008; Indrebo, 2008). Action must be taken now to improve the health and
welfare of already suffering breeds and to protect the future of these dogs.
References
Calboli, F.C.F., Sampson, J., Fretwell, N., Balding, D.J. (2008) Population Structure and
Inbreeding from Pedigree Analysis of Purebred Dogs. Genetics 179, 593-601.
Glazewska, I. (2008) Genetic diversity in Polish hounds estimated by pedigree analysis.
Livestock Science 113, 296-301.
Higgins, A., Nicholas, F.W. (2008) The breeding of pedigree dogs: Time for strong leadership.
The Veterinary Journal 178, 157-158.
Indrebo, A. (2008) Animal welfare in modern dog breeding. The role of the veterinarian in
animal welfare. Animal welfare: too much or too little? The 21st Symposium of the Nordic
Committee for Veterinary Scientific Cooperation (NKVet), Væløse, Denmark.
Jensen, V.F., Beck, S., Christensen, K.A., Arnbjerg, J. (2008) Quantification of the
association between intervertebral disk calcification and disk herniation in Dachshunds.
Journal of the American Veterinary Medical Association 233:7, 1090-1095.
Jensen, V.F., Christensen, K.A. (2000) Inheritance of Disc Calcification in the Dachshund.
Journal of Veterinary Medicine. Series A, 47, 331-340.
McGreevy, P.D. (2008) Sick as a dog: outraged by the health problems pedigree dogs suffer,
Paul McGreevy argues that it’s high time dog breeders threw away the rule book. New
Scientist 200:2677, 18.
McGreevy, P.D., Nicholas, F.W. (1999) Some Practical Solutions to Welfare Problems in Dog
Breeding. Animal Welfare 8, 329-341.
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Nicholas, F.W. (2003) Introduction to Veterinary Genetics, 2nd edn, Blackwell Publishing,
Oxford, UK.