Reader Question -- Why do the Dosage Index and TrueNicks Score Seem to Disagree Sometimes?
Written by sgillies | Feb 03, 2009 |
Reader question: Hi, Scot. I have read the history behind and understand what the DP, CD, and DI figures
stand for but my question is:
Why does it seem that good or higher DP numbers are sometimes in conflict with
the nicks? In nicking my mare with stallions I'll get higher or better DP
numbers with a "C" nick then with an "A".
I guess the follow-up question would be does anyone pay attention to DP, CD
& DI numbers anymore?
Thanks for your time..............
Scot's reply: Hello Jim. Thanks for your note. Great question!
Dosage and sire-line nicks
have a few similarities but are quite different tools.
Where Dosage looks for the
influence of stallions in a given pedigree, it does not distinguish where each stallion appears in the
pedigree - it could be the sire of the subject horse, or it could be the
maternal grandsire of the second dam. (Dosage
accounts for how close the relationship is in generations, but not its specific position
within a pedigree.) Dosage theory is
based on a manually-compiled list of stallions that are deemed influential
mostly because they have large numbers of progeny and are thought to impart a
specific aptitudinal influence on their get. Dosage does not factor the effect of all stallions, only those deemed "chefs de race."
A "nick" also looks
at stallions in a given pedigree - but it factors specifically the direct sire
(or tail-male sire line) and the broodmare sire (or tail-male damsire
line). TrueNicks calculates sire-line
affinities based on the EXACT sire-line cross of the subject horse, and it is based not
on theorized influences but on statistics (historical results), looking at
every instance of the cross based on The Jockey Club's registration data.
Many breeders find that both
systems have value. Neither tells the
full story -- no system in the world can do so! -- but each tells you a bit more
about the pedigree that you're looking at.
We include a Dosage profile on our TrueNicks reports (along with
inbreeding notations and a list of the best horses bred on the cross) as
additional tools that help breeders to interpret a mating. Alan Porter of TrueNicks likes to call this
His thought is that TrueNicks is a useful tool on its own, but is most
valuable when viewed with the perspective of other pedigree influences.
TrueNicks ratings are calculated independent of
Dosage. Many sire-line crosses have poor
affinities, even if the individual stallions are top-notch (and therefore have elevated Dosage scores). On the other hand, stallions that have not (yet)
been deemed a "chef-de-race" for Dosage calculations are often quite
useful breeders, and might prove to have a positive nick when crossed with
daughters of another sire line.
I will also point out that we should be careful when referring to "high" and "low" dosage numbers. The Dosage Profile (DP) is a set of five numbers indicating apparent aptitude based on sires in the subject horse's pedigree. The DP can range from a sum of zero all the way up to 64, depending on how many "chefs de race" are in its recent bloodlines. The Dosage Index (DI) is a very different number -- it is a ratio of the speed profile to the stamina profile, with higher numbers indicating "speed" and lower numbers indicating stamina orientation. (Additional information on Dosage can be found here: A Brief Review of Dosage.)
I discussed this topic with TrueNicks co-founder Alan Porter, and he had additional insights: "For
me, the key difference between nick ratings and Dosage is that one is intended
to measure affinity, and the other potential aptitude. It is possible to have two matings with A++ nick ratings, one
with a low Dosage Index (indicating stamina) and one with a high index (indicating speed). In either case the mating is a good nick, and whether
the dosage is regarded as "good" or "bad" depends upon the type of horse you are hoping to breed."
As for your follow-up: I've found that U.S. breeders have shown
considerable faith in Dosage theory, as have handicappers worldwide. The Dosage program is a bit less popular abroad -- it's
seen as somewhat of an "Ameri-centric" approach to pedigree analysis
because most of the stallions included are U.S.-bred or -based.
Hope that this has been useful.