Live Cover and genetic Diversity--What Diversity?

[vineyridge]

I just did some research on the top 200 TB sires in Australia in 2011--at least I think it's the current list. I did not get it directly from the originating source.

But here are the results:
Australia
Northern Dancer (Nearctic/Nearco/Phalaris/Stockwell/Eclipse)
Danzig
63 of top 200
5 of top 10
7 of top 12

Fairy King
8 of top 200

Sadler's Wells
10 of top 200

Storm Bird and Storm Cat
11 of top 200

Other Northern Dancers--Be My Guest, Nureyev, Nijinsky
24 of top 200

Total Northern Dancer 116 of top 200

Other Nearctic (Nearco/Phalaris/Stockwell/Eclipse)
2

Sir Tristram (Turn-To/Royal Charger/Nearco/Phalaris/stockwell/eclipse)
11

Red Ransom/Roberto (Hail To Reason/Turn-To/Royal Charger/Nearco/Phalaris/Stockwell/Eclipse
5

Halo (Hail To Reason/Turn-To/Royal Charger/Nearco/Phalaris/Stockwell/eclipse
4

Total Turn-To
20

Nasrullah (Nearco/Phalaris/Stockwell/eclipse)
12

Zeditave (Nearco/Phalaris/Stockwell/Eclipse)
4

Total Nearco
154

Tom Fool (Pharamond/Phalaris/Stockwell/Eclipse)
4

Mr. P (RAN/ND/Sickle/Phalaris/Stockwell/Eclipse)
29

Total Phalaris 187

Princequillo (Prince Rose/St Simon/Eclipse
3

Hyperion (Gainsborough/Bay Ronald/Hampton/Newminster/Eclipse):
Thatch
1
Bletchingly/Biscay/Star Kingdom
5
Tudor Minstrel
1
Total Hyperion
7

Total Eclipse 198


My Babu/Tourbillon/Herod
1

In Reality/Man O'War/Matchem
1

Edited title to correct typo. Thanks for pointing it out.

[Toccet02]

what's a liver cover . . .??? hah

[Pan Zareta]

Obviously, there's more to a pedigree than just the sire line but the recently published report by Binns et al. suggests that larger stallion books and shuttling are substantial contributors to diminished diversity within the TB. Imho, without mandatory live cover that diminishment would only accelerate.

[brogers]

Steve Harrison of Thoroughbred Genetics has maintained for some time that there is an ideal level of inbreeding in the thoroughbred for elite performance. Unfortunately this is not something that you can do just looking at a 5x. You have to actually genetically measure the level of inbreeding and homozygosity. He maintains that in a lot of cases the thoroughbred is not inbred enough!

[vineyridge]

Can you imagine what the results would have with with shuttling and/or AI with St Simon?

[vineyridge]

Steve Harrison of Thoroughbred Genetics has maintained for some time that there is an ideal level of inbreeding in the thoroughbred for elite performance. Unfortunately this is not something that you can do just looking at a 5x. You have to actually genetically measure the level of inbreeding and homozygosity. He maintains that in a lot of cases the thoroughbred is not inbred enough!

Well, that depends on whether you believe the only purpose of the TB is flat racing.

[xfactor fan]

The only thing a sire line tracks is a Y chromosome. And given that there isn't much diversity in the content of the equine Y, this is kind of a null problem.

So the Y chromosome from the Darley Arabian, Godolphin Arabian, and Beyerley Turk are pretty much identical. So what does it matter if it came down to modern TB's via one sireline or another?

What matters is not the Y, but all the rest of the chromosome.

[vineyridge]

The only thing a sire line tracks is a Y chromosome. And given that there isn't much diversity in the content of the equine Y, this is kind of a null problem.

So the Y chromosome from the Darley Arabian, Godolphin Arabian, and Beyerley Turk are pretty much identical. So what does it matter if it came down to modern TB's via one sireline or another?

What matters is not the Y, but all the rest of the chromosome.

I'm not sure I agree with this. I've found or believe I've found that TBs with a mixture of all three sire lines on the first page are just better. Whether it's the effect of outcrossing or whether something else is going, I wouldn't venture to say. But the effect is there.

[DDT]

vineyridge

The Y chromosome is a sex determinant and carries no genes going to performance. The many champion fillies and mares throughout the history of the breed tend to substantiate this because females do not have a Y chromosome, only males have a Y passed down the line from father to son. People tend to forget that all of the male descendants of Northern Dancer, Bold Ruler, Hail to Reason, Mr. Prospector, and many others from the same sire line have the same Y chromosome, it is the other 63 chromosomes and genes that make the difference and Mother Nature makes sure that each horse is unique in its genetic makeup, even full siblings.

I also agree that AI would contribute substantially to diminished diversity, not to mention what it will do to regional stallion markets. It would offer many new choices for the regional breeder at the expense of the regional stallions.

DDT

[diomed]

Steve Harrison of Thoroughbred Genetics has maintained for some time that there is an ideal level of inbreeding in the thoroughbred for elite performance. Unfortunately this is not something that you can do just looking at a 5x. You have to actually genetically measure the level of inbreeding and homozygosity. He maintains that in a lot of cases the thoroughbred is not inbred enough!

I have long felt that the TB is becoming less inbred than it used to be. Perhaps, it's something the breed needs to go back to? If you cannot see it in 5 generations, is it a deeper concentration of linebreeding? (I like to call that "critical mass".lol).

[ElPrado]

I just thought of something. Louis would explode if he read this thread.

[Shammy Davis]

http://www.nzerf.co.nz/Attachments/Are% ... ansfer.pdf

[Bast]

I just thought of something. Louis would explode if he read this thread.

No, he'd just come up with new categories of FB/NFB.

[vineyridge]

I do have a question. How many variants of the Y have been identified in the TB? I know that the Y is basically the same for all male horses, but it does have a few variants. If one of those variants has to do with testosterone or androgen levels, that would make a huge impact on performance capability, wouldn't it?

[DDT]

vineyridge

It could yes, but that still does not explain why there are superior females that carry no Y, so my guess, and a guess is all I can offer, is that the Y carries no known genes going to performance.

DDT