Dosage Index, foaling dates for 2023 Kentucky Derby contenders

The key handicapping factors for the Kentucky Derby (G1) revolve around performance on the racetrack, from stakes results to speed ratings and morning works. Yet there are other data points, long predating a horse’s racing career, which some handicappers take into account – foaling date and the Dosage Index.

Too early or too late?

With a Northern Hemisphere breeding season that begins around mid-February, the earliest foals are born in January. That’s not an advantage, though, when it comes to the Derby. No Derby winner since Grindstone (1996) was foaled in January. In the 2023 field, Kingsbarns (Jan. 17) is the only one who will have to defy that stat.

At the opposite end of the spectrum, later foaling dates could suggest that contenders have not reached their physical peak yet by the first Saturday in May. Verifying (May 11) and Hit Show (May 9) are the youngest, with April 30 baby Practical Move next.

At the same time, it doesn’t pay to be too doctrinaire about birthdays. The anti-January factoid could give rise to some explanations, but it also has to be viewed in the context of overall numbers. How many mares are bred early enough to deliver a foal toward the beginning of the year, compared to the height of the season in spring? 

Late foals aren’t universally behind the developmental curve either. A case in point is the 2019 Derby, when Maximum Security (born May 14) was disqualified, Country House (May 8) promoted to the victory, and Code of Honor (May 23) awarded second.

As with any handicapping tool, foaling dates are best assessed as part of the horse’s overall profile. If you otherwise like a contender, don’t over-interpret the birthday and let it dissuade you.

Of dubious value, to me, is the pedigree-derived calculation known as the Dosage Index. I’ll explain further, below the table for the 2023 Derby field (in post position order).

As a pedigree theory, Dosage has a much longer and richer history than its rather forced re-application as a pointer to Derby stamina. I won’t repeat all of my arguments against its methodology, but suffice it to say that the premise is irremediably flawed for any handicapping purpose. When you realize how the Dosage Index is calculated, it starts to look more like myth than math. So does its 4.0 “maximum” threshold for Derby hopefuls.

Only a few, ultra-elite sires in the first four generations of the pedigree count toward the formula, and maternal influence is completely ignored. Even worse, the list of “chef-de-race” sires is becoming obsolete and losing whatever utility it once had. Old patriarchs are retreating beyond the four-generation cutoff with the passage of time, and the list is not updated effectively to include current supersires. As a result, the Index is calculated from fewer points, an extremely limited data set that can mislead.

Case studies of Dosage Index problems

Practical Move is a great example. His 3.00 Dosage Index (DI) is entirely derived from the presence of Seattle Slew, who gives him a grand total of two points in the fourth generation. That’s it – two points, which according to the formula, give him a 3.00 DI. I love the 1977 Triple Crown winner, a terrific influence in pedigrees, but it strains credulity to imagine that he has a greater impact than the top sires closer up. Such heavyweight stallions as Into Mischief and Distorted Humor add literally 0 to the formula.

If you imagined that Derma Sotogake’s DI of 3.00 is attributable in some fashion to Sunday Silence, you’d guess wrong. The breed-shaper is not a chef-de-race. Derma Sotogake’s figure is leaning on the paltry four points he receives from two ancestors in the fourth generation, Awesome Again and Sunday Silence’s sire, Halo.

The problem of who counts, or not, is also why Rocket Can (4.33) and Angel of Empire (9.00) trespass against the ostensible 4.0 limit.

Rocket Can is the son and grandson of two dominant North American sires, being by Into Mischief and out of a Tapit mare. Yet he receives 0 toward his Dosage calculation from either of them. His second dam’s sire, Hall of Famer Tiznow, is also left out. It’s not exactly going out on a limb to suspect that Tapit and Tiznow can help a bit in the stamina department.

Angel of Empire is being penalized, so to speak, because his second dam’s sire, Carson City, is a chef-de-race on the speed spectrum. And he is. But in reality, his influence in the pedigree is surely mitigated by some pretty hefty names who are not chefs-de-race – Empire Maker, Pioneerof the Nile, Bernardini, and Deputy Minister. Supersire Storm Cat and Miswaki are other ancestors that Dosage simply doesn’t include.

In recent years, Steve Miller picked up the baton to add Unbridled’s Song as a chef-de-race. That’s why there are two different Dosage Indices listed for the Derby contenders with him as an immediate ancestor (Two Phil’s and Tapit Trice). If you include Unbridled’s Song according to Miller’s designation, he actually raises the DI; i.e., he adds more toward the speed than stamina column. Thus the newer figure is listed second, in parentheses, with the old-school DI first.

These case studies illustrate why I can’t accept Dosage as a signal to a horse’s aptitude for 1 1/4 miles on the first Saturday in May.

For historical comparisons, here are the foaling dates and Dosage Indices for the past 25 Kentucky Derby winners. Thanks to J. Keeler Johnson for maintaining the data and updating this table every year!