It's a proven fact that most dog health issues are caused by recessive genes. If one dog sires too many of the next generation, those recessive genes will meet up when half-siblings and other descendants are mated. It does not matter how healthy the stud dog is; reduced genetic diversity will eventually lead to the familiar problems of inbreeding.

Inbreeding and line-breeding in working dogs

In the world of pedigree dogs, there is a fine line between line-breeding and inbreeding. Successful inbreeding is simply called line-breeding. Of course, every breed of dog we have today was produced by line-breeding, which is the art of mating closely related dogs together to fix in their genetic make-up the qualities or conformation the breeder is looking for. Mating father with daughter or brother with sister increases the chances of the offspring sharing an identical gene derived from the same ancestor.

Most breeds were developed so long ago that there are few records of how that particular type of dog was produced. We do know that cockers and field spaniels derive from the same ancestral stock, the cocker not gaining its place in The Kennel Club’s studbook as a separate breed until 1893. In the past 50 years cockers have diverged markedly again, with selective breeding for either showing or working resulting in very different dogs. A similar thing has happened to most of our native gundog breeds.

There is just one gundog for which we have a detailed record of how it was established, though the word “manufactured” would be equally apt. This is the Korthals griffon, named after its creator, Eduard Korthals. Born into a wealthy Dutch family, in 1873, at the age of 22, Korthals set out to create his own all-round shooting dog. He started with seven pointing griffons and then carefully line-bred until he succeeded in producing the sort of dog he was aiming for.

It took him 20 years to achieve his goal. The result: a dog that Korthals called the wirehaired pointing griffon, the name by which it continues to be known in the US. Korthal’s success depended on the ruthless elimination of those puppies that didn’t fulfil his ideal. He bred more than 600 but kept just 62. Today the breed is most numerous in France, while its popularity is growing in the UK.

It says a lot about the dogs that Korthals selected that the breed remains as healthy as it is today. However, because it has remained a hunting dog Continental breeders have concentrated on health and ability rather than looks. Today line-breeding of this type is frowned upon, though it was only three years ago that The Kennel Club outlawed the registration of the progeny of father/daughter, mother/son or brother/sister matings.

If line-bred dogs inherited only their parents’ best features there would be no problem but, alas, they get the bad ones, too. This greatly increases the chances of genetic defects and hereditary diseases being passed on to successive generations. Inbred animals also suffer from poor reproductive performance and are seldom as robust or long-lived as those that have been out-bred.

It’s now possible for breeders to avoid inbreeding by using The Kennel Club’s excellent Mate Select program, developed in conjunction with the Animal Health Trust. Mate Select reveals an individual dog’s inbreeding coefficient, or CoI, plus that for the breed in general. Enter the dog’s full registered name into the Mate Select website, click on genetic diversity and the CoI is displayed.

The CoI is hugely revealing. For example, a CoI of 12.5% indicates that there is a one in eight chance that a dog will inherit the same version of a gene from the same dog that appears in both the sire’s and dam’s pedigree. The puppies born to a mother/son, father/daughter or brother/sister mating would be at least 25%, while the CoI of puppies resulting from a grandfather/granddaughter mating would be at least 12.5%. From a health viewpoint, the lower the CoI the better.

Checking the CoI of several leading studs from working gundog kennels makes depressing reading. With few exceptions, the figures are above the breed average, some considerably so. This reflects the impact that popular stud dogs – usually championship winners – have had on a particular breed. It’s not unusual for the same stud dog’s name to appear several times on both sides of a dog’s five-generation pedigree.

It often takes some time for the impact of such inbreeding to become apparent. The pedigree of most flatcoat retrievers includes a dog named Shargleam Blackcap, winner of Crufts in 1980. He sired 252 puppies from 47 litters, and many people believe it is his influence that has led to the high rate of cancer in the breed today.

It’s a proven fact that most dog health issues are caused by recessive genes, so if one dog sires too many of the next generation then those recessive genes will meet up when half-siblings and other descendants are mated. Nor does it matter how healthy the stud dog is, as reduced genetic diversity will eventually lead to the familiar problems of inbreeding.

The solution, of course, lies both with the breeders and the puppy buyers. Owners of bitches should select stud dogs from unrelated kennels and not opt for the most fashionable dogs of the day. Buyers of puppies should be aware of the potential problems of animals that have similar lines on both sides of the pedigree. A pedigree full of red ink, denoting field trial champions, is not necessarily a good thing. The Kennel Club already restricts the number of registered litters a bitch can have to four. It is high time it considered restrictions on the use of stud dogs, too.