The Science of Horse Racing: When Is Pedigree Useful?

October 19th, 2023

Crack open a program on any given day at the races and you will see a long list of familiar names under the entries. Each horse you see in the paddock comes from a sire and a dam, many of whom had notable careers on the racetrack that are continuing in the breeding shed. Your acquaintance with those names imbues a confidence in that starter, but the quirks of genetics, an unpredictable mix of both good and less desirable traits, are truly at the heart of what that horse will do once he breaks from the starting gate.

Understanding the influence of sire and dam and the right time to consider pedigree can make that information a useful part of your handicapping routine and give you more data to help you decide where to put your wagering dollar.

A Little Bit of This or That

Webster’s Dictionary defines a pedigree as “a register recording a line of ancestors,” but in this instance, pedigree also means, “the recorded purity of a breed of an individual or strain.” Each racetrack program or past performance features an abbreviated pedigree for each entrant, listing immediate ancestors like sire, dam, and damsire. Alongside previous starts and workouts, pedigrees can give fans an idea of what to expect from a horse — to some extent.

Biologically, both humans and horses get half of their genes from each parent. However, which genes and their combinations are harder to predict. If you have four horses from the same parents, each likely inherits different combinations of genes in their half; despite their common parentage, each can be different colors and sizes and perform in vastly different ways both on the racetrack and in the breeding shed. For example, William Woodward’s broodmare Marguerite produced seven foals by Sir Gallahad III. Of those seven, only one was not a bay, none were chestnut like her, and only her first foal, Gallant Fox, achieved at a high level, though two others were stakes winners.

What mechanism explains this difference in horses that share a common parentage? According to pedigree expert Frank Mitchell, “in pure genetics, it's 50/50, but I think it's a reasonable observation that the mothers of horses have a greater influence on their progeny genetically.” 

This assumption is borne out by practices within Thoroughbred and sporthorse breeding; most breeding lines are traced through mares rather than sires, to the point that numeric designations assigned to different families are attached to specific foundation mares. For example, champion mare Beholder comes from family 23b, which can be traced back to a Turkish mare foaled in 1770. Descendants of this family also include Triple Crown winner Affirmed, influential sire Domino, and Kentucky Derby winners Zev, Winning Colors, and Mine That Bird.

Fellow expert Jessica Tugwell echoes that assertion, saying that “[while] both obviously are influential, my analysis definitely focuses more on the mare just because I think that that is where you're going to find things that other people aren't looking at. So, you're going to find value that way.”

One constant in the science of genetics is mitochondrial DNA, which is inherited from the mother. This type of DNA mutates at a slower rate than nuclear DNA, found in a cell’s nucleus, which allows us to trace the maternal influence on offspring more readily. 

Alongside this is the phenomenon that traits are passed down in groups rather than one by one. As Mitchell observes, “the general thought among geneticists is that there are genetic bundles, and that if you get some of this bundle and some of that bundle, all of a sudden they kind of light up. Rather than just being one gene out of thousands, there tends to be more clusters or bundles of genes that may or may not be turned on generation to generation, but that in combination are probably causing this big burst of racing or production.”

The caveat with this theory is that we cannot know when certain packets of desirable traits have been passed down until certain points in each horse’s life. Going back to our example of Marguerite, Woodward could not have known what each foal she had by Sir Gallahad III was going to be until they were born, started training, or even had a few starts. To understand how a stallion will fit with a particular mare involves tracking how that stallion works with families similar to the mare’s and so on. 

A Question of When

When it comes to handicapping, though, just how much does pedigree matter? How many generations matter to our race-day wagers? Mitchell looks first “at the sire and the dam first, because those are the two influences you cannot escape. You get back a generation, or especially two generations, and a lot of that is gone.” Tugwell echoes that in her observations: “Generally from a handicapping perspective, I'm not really going to look at more than sire, dam, and damsire.”

When looking at a horse’s pedigree, most handicappers might look at the first name given, the sire, and put less stock in it than the second one, the dam. Mitchell, though, has a different approach: “I think the most influential horse on the page is the dam. Most look at the sire, and the reason is that they recognize the sires. Most of the dams are just winners or unraced or minor [stakes winners].” Their smaller sample size plus their oversized influence on their progeny make looking at the female side more of an indicator of what a horse can be. 

As Tugwell explains, “if, for example, all of the mare's foals took two to four starts to break their maiden, maybe I don't want this horse on debut. Maybe I'll give this horse a start or vice versa. Or, hey, this horse is out of a mare who has three first-time winners and is by a stallion who can get a precocious horse. Let's try that first out.”

For horses that have several starts under their belts, though, pedigree is less of a factor because their past performances are a more reliable metric for assessing future performances than pedigree. Instead, knowing a horse’s ancestry is most useful in two instances: 1) horses making their debut and 2) horses doing something new, like attempting classic distances such as 1 1/4 or 1 1/2 miles.

For horses making their first start, “you don't have very much to work with,” as Mitchell observes. “So, pedigree is most useful to handicapping in those first two or three starts.” As for horses trying something new, like running in the Kentucky Derby, Tugwell sees that understanding trends among a horse’s ancestors, especially on the dam side, can be useful for choosing your picks: “in my experience, the really good horses are going to have repetitions [in certain ancestors], especially of the female family, which is why I like looking at the female family numbers.”

As with past performances, pedigree is more about looking at trends among families on both the sire’s and the dam’s side, and then assessing how that plays into your assessments of a horse ahead of that next race. Deciding when to use that data becomes the key to unlocking its value.

Another Tool for Handicappers

The next time you are at the racetrack, that sire and dam information given in the day’s program may not be as helpful as you might think. As Frank Mitchell sees it, “in most instances, especially for handicappers, you don't need pedigree. It’s a distraction.” Rather past performances are more effective unless a horse is doing something new, like a surface switch or a change in distance. In those cases, Tugwell sees “the single biggest edge that a handicapper can get is just by looking at the mare’s produce record. To me, that is the one thing that fewer people are going to be doing that is going to give you something significant.”

Ultimately, pedigree can be valuable in predicting a horse’s potential performance, which can be helpful when deciding which stallion to breed to or which yearling to buy, but at a certain point, is secondary to earlier starts. If you are assessing a maiden race or deciding how to bet on the Kentucky Derby, then pedigree can be another tool for your wagering day. Knowing what to look for in that horse’s family can yield a useful angle the next time you are at the races.