The thirst for speed….

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Some horses are fast, and some horses are Secretariat. After the great horse’s death an autopsy revealed that his heart was about three times as big as it should have been, certainly a prescription for early mortality. The greatest racer of them all seems likely to have been a biological freak, where some developmental or genetic quirk allowed him to pound away with a macro-heart. None of Secretariat’s offspring replicated his magnificence. This makes sense, a classic case of regression to the mean. If one assumes that Secretariat’s massive but healthy heart was the byproduct of an exceedingly rare combination of beneficial genes, then sexual reproduction will likely break apart such favorable variations.

But there could be other reasons that Secretariat’s offsprings weren’t quite what he was, circulatory physiology aside. A new study has just come out which concludes that mitochondrial genetics might play a crucial role in the respiratory performance of a horse.

Importantly, we have observed that there is also independent and extensive functional mitochondrial gene variation in the current thoroughbred racehorse population and that significant associations exist between mtDNA haplotype, as defined by functional genes, and aspects of racing performance.

Mitochondria are of course only passed through the female line, so none of Secretariat’s offspring would have had his particular respiratory engine. You can read the full paper on the site of the company that is sponsoring this research. I can’t help but wonder if some Arab sheikh knew this all along….

16 Comments

  1. Interesting that no mtDNA line has become fixed among thoroughbreds.

  2. Are there any other such characteristics that are passed via the mother or father?

  3. Good stallion get about 20-30 broodmares a year. The broodmare only has one foal a year. This is why the male side is much more dominant in what breeders look for.

  4. Hmmm, perhaps brain power is related to mtDNA as well?

  5. Good stallion get about 20-30 broodmares a year. The broodmare only has one foal a year. This is why the male side is much more dominant in what breeders look for. 
     
    Thoroughbreds have been bred very intensely for a long time. If one line of mitochondria were superior, I’m sure it would have become fixed by now.

  6. great article.

  7. Good read. My Dad breeds race horses as a hobby, and we used to have a champion Irish Draft mare when I was a kid, so I know a little about horses. 
     
    I find it strange that the article assumes that similar mtDNA sequences in Irish Draft and Thoroughbred, are because the Irish Draught was improved by crossing with Thoroughbreds, when most horsey people know that to improve stamina into Thoroughbreds, you cross them with Irish Draughts!!

  8. pconroy,you are right. 
    thoroughbreds are also riddled with deleterious reccessives because they have been bred for speed forever. 
    you outcross to mask stuff like parrot mouth, shelly hooves, and long cannons. 
     
    and temperment. ;)

  9. I’ve heard about the enlarged heart before. My pet theory is that they had the horse on steroids. Hey they work for human runners and cardic enlargement is a known side effect of steroid use.

  10. It would also be intereting to examine the oft repeated claim that many if not most of the original “Arabian” progenitors of the modern Thoroughbred were actually partially or fully akhal-teke horses from the Turanian region!

  11. pconroy,you are right. 
    thoroughbreds are also riddled with deleterious reccessives because they have been bred for speed forever. 
    you outcross to mask stuff like parrot mouth, shelly hooves, and long cannons.
     
     
    I thought it was against the rules
     
    Also: That page points to an interesting explanation of equine color genetics.

  12. oh, david. 
    what jockey club say and what jockey club do are two different things. 
    “line-breeding” is standard practice, and that is consanguinous mating. 
     
    pconroy, all tbs can trace their descent from three arab foundation sires, the Godolphin arabian, the Darley, and i forget-the-other. But i don’t think any of them (reportedly) had that distinctive akhal-teke golden color. at least one was a blood bay. 
    interestingly, that is not mentioned in your link either. 
     
    Pryzwalski’s hourse was actually saved from extinction by zoo stock. the wild population had been slaughtered to the point that there wasn’t enough genetic variability in the remnents of the wild herd. 
    (i learned that in Pony Club)

  13. Matoko, 
     
    I agree with your comment regarding the Jockey Club – rules are made to be broken. I have withnessed the “swapping” of official bloodstock documents at least once – and am not sure how frequent this practice has been. The original article mention mistakes in some lineages, this may account for this? 
     
    As regards deep ancestry of the Thoroughbred, this article states that at least one of 3 putative founding sires,

  14. article truncated… 
     
    As regards deep ancestry of the Thoroughbred, this article states that at least one of 3 putative founding sires, the Byerley Turk may have been an akhal-teke, as well as Arabian horses in general having some akhal-teke bloodlines in them.

  15. “line-breeding” is standard practice, and that is consanguinous mating 
     
    Well, it didn’t say anything’s wrong with that. 
     
    But as I understood it, new blood is not allowed. 
     
    I have withnessed the “swapping” of official bloodstock documents at least once – and am not sure how frequent this practice has been 
     
    If you are right about that, then that changes everything.

  16. Like most people, I am only an occasional racing fan, as I watch only the triple crown races. 
     
    NTL, I have heard knowledgeable commentators state many times that endurance comes from the dam. I have assumed that this folk wisdom, if true, implies that mitochondrial DNA control endurance. If the mitochondria mediate metabolism, this connection seems very reasonable.

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