nice to know standard health aussie links interesting
Please also use the link to ASGHI
Genetically Clean Lines by C.A. Sharp
Dogs have around 100,000 pairs of genes. Every dog has a 4 or 5 "lethal equivalents." A lethal equivalent is a gene which, if matched up with another like it, will result in the death of the animal. All dogs also have a variety of genes that code for lesser ills and inconveniences. With that in mind, there is no such thing as a completely "clean" dog or line.
However, a line might be "clean" of a particular problem if that problem has never been known to occur there. For example, based on the information the author has on Collie Eye Anomaly, she can say that most working lines are "clean" of that disease. The breed is, on the whole, "clean" of Progressive Retinal Atrophy because it is extremely rare.
Every line will have strengths and weaknesses. For example, if a line is known for cow-hocks, that is a genetic problem in that line. It's not a disease or gross defect, but it is faulty and it is inherited. The more inbred a line, the more likely that serious problems will come to light because the process of inbreeding concentrates not only the good genes the breeder is trying to capitalize on, but whatever bad ones are there also. Example: The litter of puppies that provided us the key to determining the mode of inheritance for CEA was inbred--it went back repeatedly to the same cross.
Given that no line is 100% "clean" of everything, what's a breeder to do? With your particular breeding goals in mind (for type, structure, temperament, performance ability, etc.) look for mates whose family history is strong where your line is weak. This means considering more than an individual, you have to consider as many close relatives as you can get information on.
Knowing the status of eyes, hips, etc. on breed foundation animals might be helpful, but only where a present-day dog (sometimes 10 or more generations later) goes back to a founder many times. Unfortunately, most of these founder dogs lived and died before anybody was checking.
Endless "ugly little working dog" vs."stupid foo-foo showdog" debate does nobody good. Working and show people have very different goals. That does not make either of them right or wrong, good or bad. That said, yes, there are more hereditary problems apparent in the show lines than in the working lines. This is not because show breeders are "bad." It is because of their different goals and breeding strategies.
Show breeders are more likely to inbreed or line breed to achieve their goals (mostly physical, easily observed traits) as quickly as possible. The use of popular sires has been a given. Only recently have we learned enough about genetics to understand that there is a downside to this breeding strategy, a strategy that we were all taught was the best way to do things. If new knowledge has revealed that it isn't the best way, that doesn't make show breeders bad, it means they have to take a step back and work out a new strategy.
Working breeders put more emphasis on performance than pedigree. The herding ability that they prize is genetically complex and therefore difficult to "fix" based on pedigree alone. As a result, they are less likely to inbreed and therefore less likely to match up the "bad" genes. Their emphasis on vigorous physical performance eliminates from consideration animals with marginal health, function or stamina. Things which might not come anyone's attention if the dog lived a less demanding lifestyle.
This is not to say that working breeders are "smarter." They didn't know any more about genetics than their show counterparts. But they were just fortunate that their selection criteria were less likely to result in bringing unwanted genes together frequently.
If a show breeder needs to outcross to get away from problems in his line, and is having difficulty finding a suitable match within traditional show lines, he should consider a working line. This is a way for a show-line breeder to bring in new genetic material and get away from the problems. There are plenty of structurally sound working dogs. While the show breeder may loose something in his preferred type, that can be regained in a generation or two. But realize that the resulting puppies will not be "working dogs." Some of them may work but odds are most will not be to the standard that working breeders would demand, and so should not be marketed as such.
Working breeders should not automatically shun a conformation breeder who is interested in their dogs. A working line stud will be not at all inconvenienced or compromised by being bred to a show line bitch.
Breeding is a crap shoot. There is no way we can know the status of every one of those 100,000 pairs of genes. Our job as breeders, whatever our goals, is to "fix" what we can by disease screening, understand the odds of the game (pedigree research) and do whatever you can to keep them in your favor with the full knowledge that every once in a while you will throw "snake eyes."