The Border Collie Bottleneck

Lusia at Lassie Gets Help puts forth Dewi Tweed, the 2010 International Supreme Champion sheep dog as proof that the “genetic bottleneck” in Border Collies is benign or perhaps a myth.

Richard Millichap’s most awesome Dewi Tweed gathers sheep in the Welsh mountains. Enjoy! [For those interested in the border collie's "genetic bottleneck," Kinloch has a link to Tweed's pedigree, with the inbreeding coefficient numbers listed for his ISDS parents and grandparents.]

Sadly, COIs for one dog’s parents and grandparents don’t really tell the story of what’s happening with the breed.  Especially when you’re only looking at 6 generations.  But let’s look at Dewi Tweed anyway.

Here’s the published pedigree:

And here’s a Legend to explain what the notation means:

The first thing you’ll notice is all the green. Every green dog on the pedigree has major trial results. I count 18 of the 62 dogs on the pedigree with major trial results.  You’ll notice that the top of the pedigree is dominated by Bwlch Taff, a major sire with 715 registered puppies to his credit, and whose genes alone comprise over 3% influence on recent dogs.  For reference, Wiston Cap has a current breed influence of over 14%, making him literally the great-grandfather of the breed.

In a normal pedigree with no inbreeding, parents each have a 50% influence, grandparents a 25% influence, and great grandparents 12.5% influence.

In the case of Dewi Tweed, popular sire Wiston Cap has a blood influence of 18.4% even though you have to go back at least 6 generations before you find him on the pedigree.  So even though he’s been gone for more than 30 years, he still holds more realestate in Dewi Tweed’s pedigree than a great grandfather.  But that measure alone doesn’t account for Wiston Cap’s impact on Dewi Tweed.  The COR is what’s called the Relationship Coefficient, and it estimates the percent of genes passed down from any specific ancestor to the target dog.  Wiston Cap’s COR on Dewi Tweed is 26.7%.  So although he only takes up the equivalent space of a great grandfather, Wiston Cap is like a grandfather to Dewi.

This isn’t too surprising given that Wiston Cap appears 156 times on a full pedigree of Dewi Tweed between the 6th and 16th generations, with the 1st generation being the parent dogs, not the target dog.

In fact, Dewi Tweed has blood from 9 of the top 10 most popular Border Collies.

What is clear from the chart is that Dewi Tweed is the product of a concerted effort to breed to a very select few popular dogs. It’s also clear that those few poplar dogs are also highly related.

This is the popular sire effect. Just look at how some of them like Ben represent a very small theoretical percent of blood but a commanding influence on the genetics.  The concentration of genes in the gene pool through inbreeding and line-breeding have allowed Ben to pass down his genes over 17 times more than would be expected from his 15 appearances on the pedigree.  You can’t magnify genes within a gene pool without marginalizing other genes.

It’s not surprising that the youngest popular sire Wisp (who has still managed to romance his way into the top 4 studs of all time) doesn’t have influence on Dewi Tweed; as of the year 2000, roughly 80% of the puppies born did not have any influence from Wisp yet. There simply hasn’t been enough time for him to work his way into more lines, but we’ve already experienced his exponential rise to fame and his influence is leveling out at 4%.

Although Donald McCaig recently said:

I’ve heard the complaint that Border Collies aren’t any healthier than other purebred dogs, that pedigrees w/o Wiston Cap (d 1979) are rare. True about Cap. And intensive breeding to a single sire was, genetically, a risky idea. As it happens, the community dodged the bullet: Wiston Cap didn’t have anything wrong with him. And there hasn’t been another Wiston Cap – the community is “flavor of the month” and what I want in a dog aren’t necessarily the same combination of virtues and vices another equally qualified handler might want.

The truth is that there HAVE been many other popular sires who have cemented their place in the breed forever and consequently narrowed the gene pool.  Here is a chart of all of them, Wiston Cap is #31154.  He isn’t even the most popular sire. That honor belongs to Cap 3036 who would have still surpassed Wiston Cap even if Wiston Cap wasn’t so highly inbred on Cap 3036 in the first place [~24.5% of Cap's genes are found in Wiston Cap].  You can see Cap’s rise to dominance happened even before Wiston Cap was born.

Luisa noted that Dewi’s parents aren’t very inbred when when we look at only very recent generations, 6 generations in the case of the supplied chart. Well, a COI6=4.4% for the sire Lad isn’t a very impressive number. That level still indicates active line-breeding, as we can see, the same sire Bwlch Taff appears twice in the third generation.  The dam’s COI6 is much better at 1%, but we can still see inbreeding on common ancestors like A. Owen’s Ben.

I entered 3149 ancestors of Dewi Tweed into my pedigree program and ran Dewi Tweed’s COI6 and got 2.27%  More interestingly, I ran Dewi Tweed’s FULL COI calculation where you take his entire known pedigree into account. This is a superior calculation and represents the true degree of theoretical allele concentration due to inbreeding and line-breeding.  Before access to genetic programs such calculations were impractical, thus the popularity of more crude measures like a COI6.  Dewi Tweed’s full COI is 9.3%

Again, while the recent breeding on Dewi Tweed’s pedigree doesn’t top the charts in gross inbreeding it does not offer us any consolation that a genetic bottleneck does not exist in the Border Collie breed. In fact, his pedigree proves that such a bottleneck does exist.

Dewi Tweed is a typical example of what’s happening breed-wide: a declining interest in breeders using excessive levels of inbreeding (like father-daughter, litter mates, etc) but the overall COI of the breed still rising at an alarming rate. COI6 numbers are falling, but full COI numbers are rising.  That fact tells us that we’re past the turning point. There’s no way to out-cross our way out of increasing COIs using only registered dogs or following the same breeding trends we have been, specifically over-breeding the “flavor of the month” trial sire far and wide.

I applaud Luisa for recognizing an amazing dog that was bred and handled by an exceptional handler, but she goes too far to suggest that his pedigree assuages what should be a serious concern over the future genetic health of the Border Collie breed.

A reprint from 10/10/10.

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About Christopher

Christopher Landauer is a fifth generation Colorado native and second generation Border Collie enthusiast. Border Collies have been the Landauer family dogs since the 1960s and Christopher got his first one as a toddler. He began his own modest breeding program with the purchase of Dublin and Celeste in 2006 and currently shares his home with their children Mercury and Gemma as well. His interest in genetics began in AP Chemistry and AP Biology and was honed at Stanford University.