Breeding dogs - how hard can it be? Handsome Male + Well-mannered Female = good looking, even-tempered Pups. Right? WRONG. so very, very wrong!!
As humans, we don't think about genetics when we 'mate'. We meet, fall in love.... and discover any genetic quirks after they occur. In the case of significant conditions, love for our child kicks in and we do whatever we can to fix, alleviate and/or manage the circumstances. For dogs things are different. Firstly, a female is having multiple pups from one pregnancy, meaning multiple chances for any genetic mutation or flaw to manifest in the pregnancy. (Think back to high school Science classes and Mendel with his beans and simple 'Dominant /Recessive' squares! It is way more complex in animals, but the basic principle applies.) Secondly, the canine parents will not be the ones caring for their offspring for life - it is the new owner.
It is therefore the role of the responsible breeder to do all they can to reduce the likelihood of producing dogs with significant genetic conditions.
So what do responsible breeders to when it comes to choose which dogs to mate together?
Genetics are involved in creating all aspects of the dog - from its colour, coat type, head shape, ear set, mouth set etc. All of these traits are more complex than they appear and cannot be guaranteed just by looking at the parents. It is necessary to go further back in the lines. (Again think of Mendel and his beans!) None of these genetic traits are of consequence to the pet owner, but since responsible breeders should be aiming to produce dogs that can be in the show ring (see previous blog post), it is a major factor when breeding. There are also some tragic conditions that are linked to certain combinations of coat colours in Great Danes that require looking back 2 or 3 generations. Something the "Backyard - I've got two purebred dogs, I'll mate them'" Breeder simply can't do)
Many serious genetic conditions cannot been seen by looking at both parents or even direct grandparents. As with many genetic conditions, they will not appear in every pup from a litter.
One of the most effective ways to genetically try to identify that there is not a severe underlying issue is to know the history / lineage of both dogs. Not just on paper, but by actively researching the dogs in the broader pedigrees and by talking with people who know and had dealings with the dogs. Of course, it is not a guarantee, ultimately a breeder is still relying on the integrity of the other breeders to be honest about any conditions; however, that is where taking the time to contact people from a number of sources and building those connections is beneficial.
Using extended pedigrees (at least 5 - 6 generations) allows the responsible breeder to find interesting, odd, unusual things (may be positive or negative) and look deeper into them. It is important to look at other progeny from a mating, not just the immediate genetic line.
Looking for longevity in a line is another key to choosing the right mating. Longevity of the dogs in a line suggests no underlying genetic conditions. Again, looking further than the direct line is important. For example, a female mated to one male may produce pups that live to on average 4 years old, but mated to another dog, produces pups that live 8-10 years.
Responsible breeders know the faults in the dogs and use this to carefully select matings that mitigate the faults and enhance the strengths of the individual dogs. They use the extensive knowledge of the lineage to predict which traits are likely to become dominant in genetic combination with others. The responsible breeder knows when hybrid vigour is likely to come into play and expected outcome. They know when to 'out-cross' and when to 'line breed'. Of course there are no guarantees - we know that mammalian genetics is incredibly complex, and that Mother Nature likes to throw curve balls every now and then - but a responsible breeder should give you the feeling that they have done all they can to product healthy dogs (that are also good-looking and even-tempered as were those in the introductory paragraph!)