These two Dogue de Bordeaux have the extremely narrow, upright nostrils that are common in the breed. This and other anatomical exaggerations are why the Dogue is included in the Kennel Club list of high profile breeds subject to separate vet checks at shows. (Photos from Wikipedia.)

As I mentioned in the previous post, I want to do a series of posts on the subject of genetic diversity. Obviously the primary focus of this blog is horses, but for this particular topic I will be jumping back and forth a bit between the world of dogs and the world of horses. The situation in many purebred dog breeds is quite dire. With few exceptions, horse breeds do not face nearly such difficult circumstances, and because of that, most breeders of horses do not face the same difficult choices. Still, the factors that allowed purebred dogs to reach this point are not entirely absent in horses. It is also true that because dogs are so pervasive in our culture, many people have had their views, particularly those about what constitutes a ‘proper breed’, influenced by the world of pedigree dogs. For that reason, I will present the situation with dog breeding as a cautionary tale for those interested in horses.

So what has happened to dogs? Three independent inquiries were made in the aftermath of the British documentary Pedigree Dogs Exposed. These produced three separate reports: the Bateson Report, the APGAW Report and the RSPCA Report. All three groups found that the health and welfare of purebred dogs were compromised, and highlighted two contributing factors. The first of these was selection for exaggerated anatomical features. The second was the dramatic increase of inherited disorders brought about by inbreeding.

These observations were not new. In 1988 the British Council for Science and Society produced a report on companion animals. It noted the problems in the following statement:

An in­creasing number of hereditary problems are being recognised in companion animals, especially dogs. Many of these are the consequences of inbreeding or breeding for genetically defective animals. Some are the result of deliberate selection for abnormal or unnaturally accentuated physical characteristics for fad or fancy.

As that quote shows, both exaggeration and inbreeding were concerns twenty-four years ago. The observations made in the three reports were not new, but this time there has been public pressure to address the problems.

It is the efforts undertaken by the Kennel Club (KC) to address the first issue – the harmful anatomical distortions – that are currently the focus of much controversy in the British dog world. That controversy has created ripples over in the American dog fancy as well, with representatives from the American Kennel Club (AKC) insisting that such measures will never be taken in the United States. Meanwhile the second largest American registry, the United Kennel Club (UKC) has stepped forward to claim the high ground in addressing the issue.

This first issue will not be the focus of the posts made here. As important as the issue is to the dog world, it is not a widespread problem facing horse breeds. With a few exceptions – extreme heads in some halter Arabians, for example – breeders are not seeking to exaggerate the equine form. Horses are not anatomically malleable the way dogs have proven to be.

(These graphics come from a Belgian blog devoted to ethics in the breeding of German Shepherds.)

It is the second category of issues – those related to inbreeding – that are the bigger concern for horses. There is no question that within the horse world, there are endangered breeds with very small populations. Many of the draft and coaching breeds have experienced dramatic bottlenecks when the engine made them obsolete. It is also true that closed stud books and inbreeding are found in some horse breeds, and that some breeds have seen a rise in genetic diseases.

So why is inbreeding – in dogs or horses – a concern? Here is what the Bateson Report had to say:

Unquestionably inbreeding can lead to a loss of biological fitness. …. Inbreeding can result in reduced fertility both in litter size and sperm viability, devel­opmental disruption, lower birth rate, higher infant mortality, shorter life span, increased expression of inherited disorders and reduction of immune sys­tem function. The immune system is closely linked to the removal of cancer cells from a healthy body, so reduction of immune system function increases the risk of full-blown tumours.

These same observations are echoed in the other two reports. All three drew upon the expertise of geneticists for those conclusions. However much inbreeding is considered a valid tool by some animal breeders, the above statement is not particularly controversial within the field of genetics. Concerns about the downsides of inbreeding are pretty consistent across a large body of studies. It is the growing awareness outside that field that is new.

A few months ago, National Geographic did a feature story on the genetic variation found in dogs. One section jumped out at me when I was reading it, in part because the implications were terrible, and even worse I suspected many readers did not realize it. Perhaps pairing it with the above quote about inbreeding will make it more obvious. (Bold emphasis is my own.)

In short, while the Victorian breeders were crafting dogs to suit their tastes, they were also creating genetically isolated populations, little knowing how useful they might be to scientists in the future. The possibilities are especially abundant for cancer, certain types of which can show up as often as 60 percent of the time in some dog breeds but only once in every 10,000 humans.

Here is a similar observation from a peer-reviewed journal article:

Selection for phenotypic traits has resulted in the latent selection of genetic diseases and some breeds now have a high incidence of particular diseases, for example, the Samoyed, which has a risk ratio if 17.3 for diabetes and the boxer which has an unusually high incidence of various cancers.

The breed specificity of particular diseases lends dogs to be ideal candidates for comparative genetic association studies.

That is the precarious position of purebred dogs in 2012. Their genetically isolated populations have several hundred known genetic diseases. Because the dogs have been maintained in small subpopulations with decreasing genetic diversity, the incidence of those diseases has risen to the point that researchers have found them to be an invaluable resource. That may be good news for those seeking answers to human disease, but it is far from good news for the dogs themselves. It certainly should give pause to breeders of other animals that are considering taking (or continuing down) the same path.

It also merits thoughtful discussion by all involved with the animals affected – those that breed them, those that exhibit them and those that welcome them into their lives as companions.

Advertisements