Do Thoroughbred Sire Lines Carry More Weight Than Other Pedigree Influences?

Reader question

Mr. Gillies - I am just getting  interested in Thoroughbred breeding.  The more I read the more I became interested in rare Thoroughbred lines and out crossing.  I have been reading your blog and just love it.  I have a couple of questions, does it matter if a horse descends from a Northern Dancer say ,  through the sire or the dam, just that the horse has him in his bloodline(since you know all the statistics which I am now just figuring out)?


Scot's reply: 

Thank you for your note -- great topic.  Basically, the question is, does a stallion's position within the pedigree cause him to have more/less influence?

Well, that's simple.  "Yes."  ... And "no."

Hope that clears things up.

When it comes to sire lines, ask 10 pedigree enthusiasts the same question and you'll get at least 10 different responses! 

Let's dig a little deeper.  Only through the tail-male line (sire, sire's sire, and so forth) is the Y chromosome passed on.  The Y chromosome is believed to carry far fewer sex-linked traits than the X chromosome, so in theory the sire does not have more influence than the dam (and perhaps has considerably less influence in many cases, especially when the foal is a colt, because then only the dam passes on an X chromosome). 

A few factors blur the picture and disallow overgeneralization, however.  The consideration of pedigrees in the Thoroughbred breed has been largely dominated by sire lines and "nicks" for most of four centuries.  I believe this has resulted in the refinement of male lines that are prepotent -- that is, they tend to pass on their traits more than might be expected from a study of equine breeding in general.

Certain sires are generally accepted to be "sires of sires" (their sons are better than their daughters and themselves go on to be useful stallions).  Others are known more for being "broodmare sires" (their daughters outperform their sons, at least in the breeding shed).  Many great stallions (including Northern Dancer) fit both roles - their bloodlines are valued both in sire and dam lines.  Some stallions are actually even more "particular" -- Spectacular Bid, for example, appears to be best when he's the second damsire (i.e,, sire of the dam's dam).

Read enough pedigree analysis and you'll start to pick up on individual trends.  Some sires' offspring are all cut from the same mold; others tend to produce foals that resemble the dam or damsire.  It's often assumed that a stallion will tend to pass on traits similarly to his own sire -- but that's certainly not an established rule.  One of my favorite examples is Fappiano, who many pedigree experts agree is more representative of his damsire (Dr. Fager) than of his own sire (Mr. Prospector).


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