Horse running through field

Measuring Dam Lines

by Roger Lyons

Every few years, around November sale time, I survey female lines to see how their rankings have shifted over time. The terms “survey” and “ranking” require definition. This time round, I pulled out the winners of stakes, as compiled by WTC, that were run from 1995 to the present and tabulated every occurrence of every dam in the female lines of these SWs going back seven generations, along with the generational distance of each occurrence.

Then I crunched the numbers as usual to find out for each dam 1) how many SWs were descended from her and 2) the average generational distance of her occurrence in the female lines of those SWs. That’s all you need in order to get a rough idea of relative contemporary influence because, if you divide the number of SWs by the average generational distance at which the dam occurred in the female lines, then you end up with an index that you can use to rank the dams in a more or less valid way–based on the number of SWs per average number of generations removed. Let’s call it the Dam Line Index (DLI).

For example, La Troienne, which ranks highest among the 70,659 individual dams represented, occurs in the female line (within seven generations) of 298 SWs (since 1995) at an average of 6.42 generational removes. That means her DLI is 298 / 6.42 = 46.42, which is the number of SWs descended from her per generation.

The average generational distance is useful because it controls to some extent for the differential opportunity of mares of different eras. Best in Show, for example, which ranks 10th, occurred in the female lines of 78 SWs and at an average generational distance of only 3.79 generations. So, the index of her influence is 20.58 SWs per generation. That’s a lot less than La Troienne, but not that much less than Escutcheon, which has the second-highest rank, at 28.21 and an average generational distance of 6.38.

Now, there’s always going to be someone who says (without thinking) that seven generations is not enough since La Troienne occurs beyond the seventh generation of some contemporary SWs. That is an untenable position, though, because, if you extend that rationale across the population of dams (not just La Troienne), there can be no generational limit that will satisfy them all.

Besides, the method already has an inherent bias in favor of the older dams. Consider that Urban Sea, dam of sires Galileo and Sea the Stars, plus other high-class sons and daughters, ranks last (362nd) among dams with a DLI of at least 7.0. She is the dam of seven SWs, but has not had the advantage of subsequent generations through which to multiply her influence. She’s almost certainly bound to be better as a tail-female influence than she ranks now, and increasing the maximum generational distance of the survey would only serve to exaggerate the bias against her.

Click here to view the alphabetical list of top-40 dam lines and here to view the same list in rank order.

More about this topic in subsequent posts.

9 comments to “Measuring Dam Lines”

  • Roger Lyons crunches figs and spits out Top 40 dam lines « Sid Fernando + Observations writes:

    […] boiled it down to numbers. Click here to see the Top 40 dam lines, according to Roger, and click here to read Roger’s post for more detailed information on how the figures […]

  • Calvin L. Carter writes:


    Great article. Thanks.

  • Greg writes:

    Roger, this is exactly the kind of useful information that breeders, yearling buyers and pedigree enthusiasts should love. It tkaes so much of the “tea reading” out of pedigree analysis.

  • sledj writes:

    May I be of a different point of view, and say that apart from Urban Sea, most great racemares prove to be disappointing broodmares, but in their 2nd generation they show some influence. Urban Sea was a silly price to win the Arc, and as such could be constued to be a freak result, ergo at the moment I still prefer to look at the maternal Grandsire as opposed to the immediate dam :~$

  • Roger Lyons writes:

    Sledj, Yes you may. And I might add my own misgiving about Urban Sea as an elite producer to yours. Dams of sires do not always prove to be the most prolific tail-female influences. The most important requirement of a foundation mare is that she produce at least two or three daughters that are themselves very good producers because in the tail-female department, sons don’t count. Urban Sea could go both ways, but at this point the female side of her production is very much open to question, as you rightly point out.

  • Greg writes:

    I wouldn’t call Sledj’s a different point of view so much as proper recognition that any statistics, lists or rankings are only tools to be used by the thoughtful who can evaluate the circumstances. They aren’t an end in themselves. Context and judgment will always count. But this list makes for a tremendous tool.

  • Elaine writes:


    I beg to disagree w/ your comment, “most great racemares prove to be disappointing broodmares.”

    In fact, every study ever done confirms a direct correlation between the success of a racemare and her success as a broodmare (ie, the better the racemare the better the producer).

    An early study by Mordaunt Milner in the British bloodstock population found that non-winning mares make up 30% of the broodmare population but only 15% of the dams of stakes winners while stakes winners make up 5% of the population but 25% of the dams of SWs.

  • Roger Lyons writes:

    Yes, Elaine, it’s true that there’s a correlation between racing performance and production, but I wonder how far that correlation goes. I wonder if it goes so far as to warrant the conclusion that the very best racemares tend to be the very best producers. Maybe, as we often find on the sire side of the question, the very best broodmares tend to come from the ranks of the runners up, rather than from the ranks of the freakishly good runners.

  • jughead writes:

    J. A. Estes has gathered considerable data to prove the contention that high racing class in the immediate ancestors is the best index of probable excellence. For example, the Futurity has been run 56 times, and 22 of its winners, or 39 percent, were the sores and daughters of stakes winning mares. Since there are so few mares of this caliber, the normal expectancy would be nearer 10 percent. A similar study by Robertson of the classic winners in England, showed convincingly that racing class of a dam is indicative of her potential value in the stud. Estes adds, “It is, more specifically, my intention to contend that it costs ten times as much to buy a pedigree without racing class as racing class without a good pedigree, and that these odds are upside down. Class without pedigree is actually a far better

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