Dosage in Plain English

By Posted on 19 Comments 5 min read 3434 views

Let’s say this, right now — in this context, dosage has no connection to doping horses. None. Nada. Zip.

If you follow horse-racing to any extent, you’ve heard the term and wondered what it meant. Maybe an explanation made your eyes glaze over. After all, you don’t need to know all the ins-and-outs.

So, this post is just a newbie’s introduction. And, if you stay long enough to read the entire post, you’ll find a little secret at the end that blew me away when I first read it.

Dosage is a statistical tool used to predict performance.

Dosage figures are based on a list that works like a “Who’s Who” of thoroughbred breeding.

About a hundred years ago, a French thoroughbred racing scholar named Lt. Col. J.J. Vuillier conducted a study of the top runners in England and France.

Vuilllier noticed that certain stallions kept appearing on those pedigrees. He studied their records and determined which characteristics they passed on.

He called these stallions the chefs-de-race or “chiefs of racing.” What’s more, he noticed that every decade or so, new stallions showed up on the list.

If you’d like to get into detail about dosage, Dr. Steven A. Roman is an expert with a website and the book DOSAGE: PEDIGREE & PERFORMANCE. Check his site and look into his book if you want to know more, lots more.

Chefs-de-race (Chiefs of Racing)

As of this writing, there are 220 stallions listed.

So. who’s among them? Legendary horses like Man O’War, Secretariat and War Admiral. So is modern stallion A.P. Indy, a leading sire whose stud fee is $300,000 for a live foal.

But who’s not on the list? For one, War Admiral’s famous-from-the-movies vanquisher Seabiscuit.

Nor is Storm Cat, the now-pensioned stallion who used to command $500,000 in stud fees.

Winning a US or UK Triple Crown title isn’t a lock for inclusion as a chef, either. Only six Triple Crown winners — three from the U.S. and three from the U.K. — are listed as chefs.

Of those US Triple Crown winners, Affirmed isn’t listed, but his famous rival Alydar is.

The Influential Genes of the Chefs

A stallion on the list is a given an aptitudinal designation that’s indicated by a letter, but it’s not S for “speed” or E for “endurance.” Think more metaphorically.

“Brilliant” is used for “speed.” And “Professional” is used for endurance or stamina.

So, B=Brilliant (speed), I=Intermediate, C=Classic, S=Solid and P=Professional(stamina).

And you read that from left to right, you can see what resembles a matter-of-degrees from Brilliant (fast) to Professional(tough).

Now, let’s go back to the chefs-de-race list.

When you look down the columns of names, you’ll see parentheses with the letters B, I, C, S, P. Some listings just have one letter, others have combinations of two.

Where the Numbers Come In

Now, here’s where dosage gets mathy and makes people’s heads spin.

When a chef-de-race is in a horse’s pedigree, a numerical value is determined by the generation that sire appears. That makes up the Dosage Profile.

The numbers are assigned along the B-I-C-S-P lines. Let’s take a look at two-time Horse of the Year winner Curlin, whose dosage profile is 9-11-17-0-1.

Remember B(rilliant) — I(ntermediate) — C(lassic) — S(olid) — P(rofessional) which means …

A Range from Speed to Stamina

No doubt, according to that layout of numbers — with so many to the left of center — Curlin is bred for speed. He’s also bred to go the distance of the Classic races like the US Triple Crown and has a bit of stamina to go the distance. Yet, he lost his Belmont Stakes bid, a 1-1/2 mile race, to the filly Rags to Riches, whose DP is 8-11-19-0-0, very heavy on the speed.

What can I say? DP is about possibilities and the Belmont is the final race of the US Triple Crown, a long campaign.

As I update this article in Sept. 2013, Curlin is turning into a hot sire. One of his sons Palace Malice won the 2013 Belmont Stakes. Perhaps one day, he’ll become a chef?

Just Probabilities, but Still …

But, statistics or no, horses are living beings who have good days and bad.

Still, handicappers and breeders pay attention to dosage as a statistic that can indicate probable performance.

A.P. Indy, when he was  still active in the breeding shed, is a good example of when the variables come together and how dosage numbers work. In his case, according to the chart, he’s an I/C. He was the 1992 Horse of the Year. Although he scratched in the Kentucky Derby, he won the Belmont, the Breeders Cup Classic, and the Jockey Club Gold Cup.

Indy’s Dosage Profile is 13-10-20-3-0.

Remember – Brilliant-Intermediate-Classic-Solid-Professional.

He’s got some speed in him, all right, but he’s also got some distance runners, too. Those numbers right of center probably contributed to that 1-1/2 mile Belmont Stakes win.

Let’s go back here, scroll down the page and take a look at Indy’s pedigree. He’s a direct son of US Triple Crown winner Seattle Slew, plus Indy’s mother was sired by Triple Crown winner Secretariat.

He’s got Triple Crown winners in close generational proximity “on the top and bottom,” as horsemen say.

Which leads us to a little secret about dosage …

Common Sense in Statistical Form

If you breed the best to the best, your odds of getting the best are better.

Now, for the secret

I wish the link were still here. But when I was first curious about dosage, I did some websurfing. I saw the dosage numbers for the 2004 Kentucky Derby, the year that Smarty Jones made his Triple Crown bid. I was amazed to look at those Dosage Profiles and see what history proved out.

That the beloved Smarty Jones did not have the pedigree to go the distance of the Belmont Stakes. His DP has very little to the right of center. But Birdstone. the winner (and spoiler) did.

Check it out – stats from Pedigree Online:

  • Smarty Jones – 10-3-8-1-0
  • Birdstone – 7-8-9-0-2

For more reading on dosage:

From Thoroughbred Champions

Dosage: Pedigree & Performance by Stephen A. Roman, PhD

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  • Jo
    December 15, 2008

    I was so glad to find this. After a lot of years following horse races, I don’t remember ever hearing the term before. I must have been too busy admiring the horses and trying to help my favorite across the finish line to listen to all that the announcers were saying.

    It takes me a little while to get my brain wrapped around the numbers but it’s definitely something I want to learn more about. The Horsey Set is a great place to learn. Thanks!

    • rhond7
      December 15, 2008

      Thanks, Jo. If anyone talks about dosage, especially on TV, it’s more likely to be mentioned briefly in those segments on handicapping — which I used to mentally tune out. Like you, I always had my faves or made my picks from what I saw in the paddock before the race.

      Also, dosage seems to have fallen out of favor. Yet, if you look up a horse’s pedigree, you see the dosage index. So, somebody’s still paying attention.

      But, like anything else, it’s just an indicator of possible potential. The bottom line is in what the horse delivers at the track.

    January 29, 2009

    I thought it was all rather common sense as anyone who has been to the track more than three times a year knows that Birdstone was the favorite in all of the Kentucky Derby Futures pools and only lost because of a stomach infection. As in all sports betting just follow the money line. But what will they say when Vineyard Haven wins the 2009 Kentucky Derby. Anything can happen in racing remember Frank Hayes and his mount Sweet Kiss! Happy hunting fellow enthusiasts.

    • rhond7
      January 29, 2009

      Thanks for stopping by, Big Red. It’s true that the Triple Crown Races bring out the casual race fans. They’re the only races that get lots of promotion and TV coverage. The sad truth is that the Breeders Cup doesn’t get much attention outside of racing. But the TC races get plenty.

      That said, a lot of variables have to align (almost like lucky stars) for a horse to win. Talent and pedigree aren’t sure things. But that’s one of the reasons why it’s all so exciting.

      Thanks for your comment.

    January 29, 2009

    I know that this doesn’t relate to the article but where is Lauren Stitch? She was the best DRF handicapper for the Belmont Stakes. This coming from a reformed chauvinist. I miss her!

  • rhond7
    January 29, 2009

    I was afraid those links would get messed up. Let’s try this again.

    She apparently took the buyout at the DRF according to this:

    And my Google search says that she’s at

  • Christ
    February 12, 2011

    Well, as long we we’re making excuses for Birdstone, Smarty Jones had career ending problems with his legs when he ran the Belmont. He’d been in ice and not out of his stall from his record breaking win in the Preakness until race day at Elmont. And he still had the heart to lose by only 3/4 of a length at a mile and a half.

    • Rhonda Lane
      February 12, 2011

      I remember seeing Smarty’s legs quivering after the Belmont. He was a game competitor and is, as of this writing, siring winners. Thanks for stopping by.

  • Augusto Slaviero
    April 13, 2012

    Hello, Could somebody tell mewhat mean the : DI , CD and GSV at the Dosage?

    Thank you

    • Rhonda Lane
      April 15, 2012

      Hi, Augusto – Good questions! Let me look into it, and I’ll get back to you here. Because you commented on this post, anything posted after this in this Comments section will go straight to your Inbox. Thanks for asking. It may take me a while – but I’ll work to get it here before Derby.

    • Rhonda Lane
      April 15, 2012

      Okay, Augusto. Here is an excellent chart that will help you with the “alphabet soup” on pedigree charts.

      I hope that helps. Here’s hoping your picks come in. Enjoy the races!

  • jessica
    November 8, 2012

    What does this Dp mean 26631
    What dose this Di mean 1.57
    What does this CD mean +0.28

    • Rhonda Lane
      November 8, 2012

      Hi, Jessica – So glad you asked about the alphabet soup on a pedigree chart.
      DI is Dosage Index, a ratio of Speed to Stamina. (More in a link I’ll provide below.)
      DP is Dosage Profile, except it’d be written 2-6-6-3-1 (is there a number missing?) – the spread of numbers is what’s explained in the post.
      CD is Center of Distribution – is a measurement for the balance between Speed and Stamina.

      I know: it’s confusing and mathified, but all it is is a way for handicappers to quantify the potential abilities in a horse’s pedigree along a scale of skills from Brilliant/Fast to Stamina/Endurance.

      Anyhoo, here’s a really good link that’ll help with your confusion. What I like about that page is that it gives you pedigrees for examples at the top of the page with a glossary below. Thanks for asking, Jessica. IMO, this dosage stuff works best when you’re picking a Belmont horse.

  • Pam
    September 17, 2013

    Curlin’s DP is wrong in this article. Smart Strike is on the Chefs list adding 8 points to both the I and C numbers. He also has one P point in Nodouble.

    • Rhonda Lane
      September 17, 2013

      WOW! Thank you for the catch, Pam, let alone for letting me know. I repaired and revised this article. If nothing else, this article needs periodic updating, especially with all the little Curlins winning at the track. Thanks again for giving me the heads-up! 🙂

  • Cason
    March 9, 2018


    I have been browsing the web like you did to understand DI and CD figures a bit more. The more I read, the more I am convinced that these figures are just probability to succeed in certain distances rather than true potential of the horse. The conformation, the inbreeding percentage of certain ancestors, and other racing environment factors will affect the results. But I like to bring out the topic of full siblings. So far I have not seen (correct me if I am wrong) a high percentage of full siblings of previously successful racehorses can perform better or even replicate their older famous siblings. If we look at the pedigree, everything is identical, isn’t it? So how can we explain the performance differences among those siblings? History may change if the full brothers of American Pharaoh and those of California Chrome can replicate their brothers or even excel way better than their brothers.

    • Vincent Silos
      January 11, 2020

      My take is that siblings are not created equal.In a perfect world, they should be equal or surpass that of the sibling, however, you have a question of environment, heart, conformation, etc. Just look at humans… I know of fraternal twins who are different than their sibling. Just my 2 cents

      • Rhonda Lane
        January 12, 2020

        So true. The old horse breeding adage of “breed your best to the best to get the best” doesn’t take “nature vs nurture,” let alone personalities, into account. Thanks for commenting.