As a broodmare sire Princequillo was responsible for 168 black type winners from 1,422 starters, or 12%. As with most other highly successful broodmare sires, Princequillo was little different from any of them in that they can all be shown to be marginally more successful as stallions. So much for the "maternal damsire effect".
The proposition that Secretariat derived his superior capabilities from the fact that Princequillo was his broodmare sire and contributed his "large heart gene" through his X chromosome, appears equally misleading. The pedigrees of stallions currently registered in The Blood Horse Stallion Register make a representative yardstick for excellence, and provide ample statistics to demonstrate the role of Princequillo in a modern day pedigrees. To summarise our findings, taking a sample of the first 320 stallions listed alphabetically in the current edition of The Blood Horse Stallion Register, we find that of the 10,000 or so male ancestors within their pedigrees, Princequillo is present a little over 150 times.
For Princequillo to be in a position in the pedigree to supply the X chromosome, we find that such criteria are met in only 40 of these cases (0.4% of all male ancestors present). In terms of the influence of Princequillo, in the event that he were able to offer "large heart" genes, Princequillo' s presence through sirelines, where he could have no capability of passing on the X chromosome, is 4 times greater than in the position where he might support the "large heart" theory. What is more, in these latter cases (where he could have capability of passing on the X chromosome) it is noticeable that these are mostly sires at the lower end of the stallions spectrum, and indeed many were at the lower end of the scale in terms of their performance on the racetrack. In the unlikely event that Princequillo had the power to pass on such special attributes, he appears to have made a pretty good mess of it!
The statistics just do not support either of the theories investigated above. A more likely explanation of what made Secretariat such a phenomenal racehorse will be explored in an article on Nasrullah to appear shortly in these pages.