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Merle Merle Breeding


snook
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I'm very new to the breed and I enjoy reading all the posts, I always learn something new- never a bad thing. I read this on the another post

Just as an ethical (well, in my book anyway) breeder wouldn't cross two merles, not matter how much ability they had, knowing unhealthy pups would be produced almost for sure,
and I was really curious why merle/merle breeding produces unhealthy pups? Is there a flaw in their genetics? I did a search and didn't find the answer.

 

I'm probably extra curious about this because my lovely pup is a blue merle- (nope, not going to breed, he's getting neutered tuesday-ouch!)

 

Anyhoo, thanks in advance for the info!

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It happens a lot more often in Aussies, because there are so many more merles, but as Border Collies become more popular and people must have their fancy colors it'll happen more often in Border Collies as well.

 

I like merle, I think it is a pretty pattern but frankly I think any breed with any chance of ending up in the hands of unknowledgeable breeders is better off not being merle.

 

http://www.asca.org/Education/Advanced/troublemerle.htm

http://www.ashgi.org/articles/color_white_fright.htm

http://www.lethalwhites.com/doublemerle.html

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For the biomechanics behind WHY excessive whites are deaf... (w.r.t Great Danes, but the last couple paragraphs pertain to all white factored dogs)

 

http://www.greatdanerescueinc.com/WhiteDeaf.html

 

also search the forums (http://bordercollie.heatherweb.com/cgi-bin...;search_forum=4) for "merle deaf" and you'll find a couple old threads on the topic.

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Here are a couple of easy to read articles on merle and white border collies from this site:

 

http://www.bordercollie.org/kpmerle.html

http://www.bordercollie.org/kpwhite.html

 

Merle-to-merle breedings have a high risk of producing deaf and/or blind pups. Those pups will be mostly white (the so-called "lethal white"). But dogs can also be mostly white because of entirely different genes -- genes at the S locus rather than the M (Merle) locus -- and this altogether different type of genetic whiteness is often called white-factoring. This type of whiteness is much more common in border collies than the merle-to-merle produced whiteness, simply because merles are not that prevalent in the border collie breed. As more and more crummy breeders start breeding for exotic colors, this situation is likely to change.

 

There are definitely breeds in which white-factoring is linked to deafness, and the Great Dane is one of them. There are other breeds where it's not linked to deafness, probably because white-factoring in those breeds does not make it any more likely that there will be a lack of pigment-producing cells in the ear. I haven't come across any real evidence that it's linked to deafness in the border collie. I would love to see a study done to determine this for sure; I suspect it would put to rest a lot of the spillover prejudice against white-factored dogs. In any case, it is very, very rare to find a merle-to-merle litter without deaf and blind mostly-white pups in it, and it is very rare to find deafness or blindness in a mostly-white border collie which was not produced by a merle-to-merle breeding.

 

Edit: Snook, I should have said that a regular merle border collie like yours, who is the product of a merle x non-merle breeding, is not at any increased risk of deafness/blindness.

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