Debates over the identity of the greatest racehorse of all time are both forever pointless and endlessly entertaining. I’ll see your 31-length Belmont win by Secretariat and raise you Frankel’s 14 straight wins. For racing’s equivalent to the hot-stove league, there is no universally valid and accepted method of comparing great horses of different eras. With the breeding season in full flower, however, the thought occurs that comparing the quality of the broodmares such greatness attracts to a stallion’s court is more amenable to statistical analysis. Debate over which great racehorse covered the best first book of mares thus might be not only entertaining but conclusive. When Secretariat retired to stud in 1974, he was the most valuable animal on the planet, with a record stud fee, and breeders naturally sent him their best mares. Stallion management in the 1970s, of course, was far different and far less aggressive than in the new millennium. At the time, the standard stallion syndicate called for 40 shares, which guaranteed one breeding right per share, plus various breeding rights for syndicate managers, leading to standard books of 40 to 50 mares. Secretariat’s syndicate numbered only 32 shares, though additional breeding rights were sold on an annual basis. That paltry number of mares would be seen as a guaranteed route to failure in today’s market, where that many yearlings by a popular stallion might be offered in a single book at the Keeneland September yearling sale. In addition, Secretariat suffered from fertility problems in his first season at stud caused by immature sperm. As a result, his first crop, foals of 1975, resulted in only 28 named foals. First books for more recent great racehorses are far more robust. Ghostzapper, the most recent American horse to retire with a record first-crop stud fee, sired 80 named foals in his first crop. Sea The Stars, Europe’s most recent superstar prior to Frankel, has 118 foals in his first crop of 2-year-olds racing this year. As shown in the accompanying table, Frankel is scheduled to cover 133 mares in his first book, and comparisons of the standard measures of broodmare quality among the four stallions lead to some interesting conclusions. First, it must be noted that the numbers in Frankel’s column and the numbers in the other three columns do not represent exactly the same thing. The numbers for Frankel represent the mares currently booked to Timeform’s all-time top-rated racehorse in his first book, while the numbers for Secretariat, Ghostzapper, and Sea The Stars represent actual foals in their respective first crops. That makes no real difference to the statistical comparisons, since fertility does not vary significantly with racing class. Whether a mare conceives and delivers a live foal in a given year is not correlated with racing or producing class. Secondly, the three main sections of the table represented by subtotals in bold type are mutually exclusive. The first criterion for determining whether a broodmare might be worthy to breed to a stallion of the quality (and price) of Frankel, Secretariat, Ghostzapper, or Sea The Stars is racing class. Thus, the first section of the table details the percentages for each stallion of Grade/Group 1 winners, Grade/Group 2 and 3 winners, and stakes winners. If a broodmare is not herself a graded stakes winner or stakes winner, the next question is whether she has produced graded winners or stakes winners. Thus, the next section of the table enumerates the non-stakes-winning mares who had already produced Grade/Group 1 winners, other graded stakes winners, or stakes winners at the time they were covered. Please note that the Grade/Group 1 winners, other graded stakes winners, and stakes winners also may have produced graded winners or stakes winners, but they are not included in the second section of the table since it is presumed that being a graded stakes winner or stakes winner is sufficient qualification. If a broodmare is neither a stakes winner or better, nor a graded stakes or stakes producer, then what are her qualifications for breeding to a top stallion? As the table shows, for a stallion of this quality, almost invariably they will be siblings to top racehorses divided along similar categories to the first two divisions of the table. Again, the broodmares counted in this section of the table were neither stakes winners nor stakes producers at time of cover. As shown in the table, Frankel has attracted the highest percentage of Grade/Group 1-winning mares to his book that the others compared, and by a substantial margin. When one considers all stakes winners, including Grade/Group 1 winners, however, the picture changes, and Ghostzapper comes out on top since 67.5 percent of the dams of the foals in his first crop are stakes winners. The percentage of stakes winners is so high in the first books of Frankel and Ghostzapper that the percentages of graded stakes and stakes producers are necessarily lower than for Secretariat and Sea The Stars. It is obvious from the various statistics, though, that except for the substantial advantage Frankel enjoys with Group/Grade 1 winners, the first books of these four great racehorses are similar in many ways. Still, it is hard to fathom the depth of racing class of Frankel’s first book. The list (kindly provided by Juddmonte) includes six winners of the English or French Oaks, four Breeders’ Cup winners, Japan Cup winner Vodka, Prix de l’Arc de Triomphe and King George VI and Queen Elizabeth Stakes winner Danedream, and two European Guineas winners. The list of top producers is just as impressive, including dams of eight European classic winners, plus the dams of Breeders’ Cup winner Midday and Preakness Stakes winner Shackleford. All of Europe’s leading breeders have sent some of their best mares to Frankel, many of them multiple mares, and several leading American breeders have mares booked to the undefeated champion as well. One factor in the success of any stallion is how well his pedigree meshes with the pedigrees of the broodmare population he serves. By the world’s best sire, Galileo, out of Kind, by Danehill, Frankel’s pedigree includes the two most successful stallions of the past 20 years in Europe, and indeed the world: Sadler’s Wells, the sire of Galileo; and Danehill, who succeeded Sadler’s Wells as England’s leading sire. Their dominance of contemporary European breeding means that one of those two names appears in the pedigrees of many of the Grade/Group 1 winners and other stakes winners in the current European broodmare population. Historically, breeders have generally tried to avoid close inbreeding, but that habit has begun to change, partly of necessity, in the contemporary breeding environment, where larger books of mares have concentrated pedigree strains, particularly those descending from Northern Dancer, like his son Sadler’s Wells and grandson Danehill, in the Thoroughbred population. Frankel himself carries a relatively high inbreeding coefficient of 2.98 percent through the first six generations due to his 3x4 inbreeding to Northern Dancer, 5x5 duplication of Buckpasser, and additional duplications of Natalma, Raise a Native, Native Dancer, and Princequillo within his first six generations. Inevitably, the average inbreeding coefficient of the 133 prospective foals by Frankel is also relatively high at 2.89 percent. All but 13 would carry at least one additional cross of Northern Dancer on the bottom side, and more than one pedigree will include as many as five total crosses of Northern Dancer. Nineteen prospective foals would be inbred to Sadler’s Wells, 12 inbred to Danehill, two to both. Despite traditional fears of inbreeding, that is unlikely to harm the racing or breeding careers of any of Frankel’s foals. Frankel is such a superior individual physically and mentally, and his pedigree is of such superior quality, that it is hard to imagine him failing at stud. Some of his high-quality offspring are bound to be closely inbred. As with Secretariat, though, the odds are stacked heavily against him siring a son or daughter as good as he was. Despite being widely considered a failure in his lifetime, Secretariat sired 8.6 percent stakes winners, including Horse of the Year Lady’s Secret, champion 3-year-old male Risen Star, and Canadian champion Medaille d’Or. His most powerful influence, though, was as a broodmare sire, his daughters producing important sires Storm Cat, A.P. Indy, Gone West, Volksraad, Summer Squall, Edgy Diplomat, Holy Roman Emperor, Dehere, and Chief’s Crown. Frankel is in the midst of covering the book of the century. Because the sire provides 50 percent of the genes of the offspring, on average, and the dam 50 percent, the predicted genetic potential of his first crop is bound to be as high as any crop in history. Only the racetrack will tell the tale. Comparison of first books   Frankel Secretariat Ghostzapper Sea The Stars Mares/foals 133 28 80 118 G1 wnrs (%) 38 (28.6%)   5 (17.9%) 12 (15%) 17 (14.4%) GSW (%) 22 (16.5%)   8 (28.6%) 20 (25%) 17 (14.4%) SW (%) 18 (13.5%)   1 (3.6%) 22 (27.5%) 21 (17.8%) subtotals: 77 (57.9%) 14 (50%) 54 (67.5%) 55 (46.6%) G1 prod. (%) 19 (14.3%)   6 (21.4%)   5 (6.3%) 25 (21.2%) GSW prod. (%)   6 (4.5%)   3 (10.7%)   5 (6.3%)   9 (7.6%) SW prod. (%)   6 (4.5%) 0   5 (6.3%)   4 (3.4%) subtotals: 31 (23.3%)   9 (32.1%) 15 (18.8%) 38 (32.2%) Sib. G1 (%) 15 (11.3%)   5 (17.9%)   4 (5%)   16 (13.6%) Sib. GSW (%)   2 (1.5%) 0   2 (2.5%)   4 (3.4%) Sib. SW (%)   3 (2.3%) 0   2 (2.5%)   3 (2.5%) subtotals: 20 (15%)   5 (17.9%)   8 (10%) 23 (19.5%) Others   4 (3%) 0   3 (3.8%) 2 (1.7%)