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Let's just hope breeders will finally understand the importance of eyescreening yearly! Even more important with this problem is having the older dogs tested! The ones you don't breed from anymore, but they are the parents of your breedingstock! There seems to be another mutation that appears at 5-6 years of age, and the DNA test for PRA rcd-4 doesn't work for that form, so eyescreening is still important, even if we have a DNA test for PRA rcd4!
I'm afraid we will have lots of carriers in our breed, so let's hope the DNA test will be available very soon.
Here lies the problem, Sue: "clearing the lines, as they did with CLAD and PRA rcd-1" was all done with the very best intentions...
But looking back we must be honest and admit that many carrieres who could have given the breed valuable input were discarded too quickly from the breed pool. All DNA health tests are extremely important but unfortunately can lead to new problems arising. The COI in Irish Setters is extremely high as the Breed Mate programme of the KC has shown. We can not afford to discard dogs from the breed pool who are not actually affected by the disease. Breeding carriers to clear must be permitted for a very long time yet unless we are to increase the COI within our breed still more - because that would mean increasing the prevailance of diseases that are not based on simple recessives but far more complex.
Wilko, I admit I was never one for maths and COI is all maths and statistics... but I must admit that the Dr John Armstrong Genetics group has helped me to understand at least part of the complex subject. You may want to look into the Canine Genetics Diversity Group (Yahoo groups).
The KC's Mate Select unfortunately does have some real shortcomings and I am sure these will be improved over time. For one thing not all dog's COI calculations are based on the same number of pedigree generations.
Back to your question concerning high COI mated to high COI giving a low COI... Just think what happens if you mate a highly inbred dog of one breed to a highly inbred dog of another breed: obviously the COI will fall rapidly. The same happens if you mate one highly inbred Irish to another highly inbred Irish from a completely different line. The resulting pups are no longer highly inbred.
But as Rosie points out, say you mate a Weimaraner to a Setter and both parents are carriers of the identical recessive mutation for an illness then obviously you will still have affected puppies. Lowering the COI will not help to eradicate the disease in this case.
On the other hand the overuse of popular sires combined with inbreeding (and this includes linebreeding) over a long period of time will mean that unidentified diseases can become widely spread in a population before the illness is discovered. This may be the case with PRA rcd4. In Gordon Setters around 50% of the population could be carriers. In Irish Setters we must wait and see...
The more I try to understand genetics the more I realize how little I understand...
Wilko, I have long held the opinion that relying on COIs to get a breeder "out of trouble" can be just a mirage - reality is that you are not breeding a COI to a COI - you are breeding 2 living animals with a genetic makeup you may think you know - but "genes" are not visible to the human eye just yet!!
COIs are not the "be all & end all" & I do think that setting a maximum allowable COI will be detrimental to the breed in the long term, given that from the pedigrees I have seen many breeders just follow fashion.
I do think we must move on from the concept of linebreeding. I also grew up with that concept. Linebreeding was needed to fix required traits in purebred dogs. But those traits are well and truly fixed by now. I fear if we continue to breed in this way we will loose much needed genetic diversity and head for disaster.
Dog breeders should not close their eyes to science.
It may put your mind at rest to look at the Kennel Clubs policy for the Gordons, I think it will be a similar policy for Irish, with no time frame set to clear the condition. I too thought that some CLAD carrier dogs were not used at stud to the expense of the breed. Too many breeders didn't want the hassle of using carrier dogs, it was mainly carriers bitches that were bred from to clear the breeders own lines.
With regard Wilco's comments on COI, breeding healthy dogs to healthy dogs is the most important thing. For PRArcd4 and where we have a condition with a DNA test, not to mate carrier to carrier, enableing us to breed the condition out without loosing any lines or excluding good dogs. Low COI dose not give you any assurances that you will not produce health concerns, it all depends on what unwanted genes are present in any dog. I put in a brother / sister mating into the KC Breed Mate program and got a litter figure of 36.8% COI, then the same bitch to a totally unrelated dog and got 0.3% COI. In the case of PRArcd4, if my bitch is a carrier and her brother is not, I will not produce affected dogs, if the unrelated dog is a carrier, the liter will produce affected dogs, which shows in this case that COI has no relevance.
Not to worry, Sue :-)
I think all we wish for is that our dogs are healthy and DNA tests are definiitely a huge benefit!