Fast Facts -- What Is the Comparable Index (CI)?

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re: Fast Facts -- What Is the Comparable Index (CI)?

sceptre — Fri, 31 Jul 2009 16:27:23 GMT

Just a quick note to clarify some of what I said, and LanceS' suggestion ("The CI needs to be adjusted for the AEI of the stallions who sired the other foals"). I've mulled this over long ago, and concluded that there was little to be gained by factoring in the AEIs of the stallions to whom the mares were bred. For example, one can also see flaws in those as well. It's possible to continue that zig-zag process (with its inherent flaws) down the generations. Would such an exercise yield, in the end, a more "accurate" number?- I doubt it would accomplish much. There are just too many variables to consider, let alone the difficulty in assigning weights for each.

re: Fast Facts -- What Is the Comparable Index (CI)?

Pedigree Shelly — Fri, 31 Jul 2009 02:47:10 GMT

Scot, You must have been reading my mind,because I wanted to ask you a question on this very subject ! Thanks for the information ! I find the AEI and the CI very useful !

re: Fast Facts -- What Is the Comparable Index (CI)?

Lmaris — Thu, 30 Jul 2009 17:50:29 GMT

Don't you just love the "prophets" who tell you they forecast the future long after it happened.

Suuuuuuure you did, da3hoss.

Funny how you missed Trippi....

re: Fast Facts -- What Is the Comparable Index (CI)?

LanceS — Thu, 30 Jul 2009 13:19:16 GMT

Sceptre makes a great point. The CI really needs to be adjusted for the AEI of the stallions who sired the other foals. For example, if two stallions have a CI of 2.00, but stallion A's mates had all their other foals sired by Storm Cat and A.P. Indy, while stallion B's mates had all their foals sired by Charismatic and Real Quiet, then clearly the mares bred to stallion B are superior to those bred to stallion A, since collectively their foals have overperformed their sires, while the foals of stallion A's mates have underperformed.

This was recognized by the USDA in their dairy bull proofs at least 35 years ago, but for some reason no one seems to want to do the same level of statistical analyses of horses as they do of dairy cattle.

re: Fast Facts -- What Is the Comparable Index (CI)?

sceptre — Thu, 30 Jul 2009 01:06:36 GMT

Good point about Perfect Soul...

The CI does offer us some useful information, but one should be careful not to overestimate its value. CI is flawed, and here are a few examples:

We are attempting to assign a number for a mare's true genetic worth. Mares, unlike many stallions, have a relatively limited number of offspring. Their overall production records are, therefore, of less statistical "significance" (less of an accurate measure of their true genetic worth) than are the records for many stallion (much larger data base of offspring)...A mare's CI is also a reflection of the stallions to whom they were bred. Imagine all those mares who were sent to Bold Ruler (had a very high AEI). Bold Ruler, cumulatively, raised the CIs of those mares bred to him ( a mare of similar genetic value bred to most other stallions would not have produced an offspring of such high A.E.I.)...Lastly, while it may be obvious to many, it is worth noting that many stallions who "improve" their mares are far inferior to those where the effect is opposite (this can easily be demonstrated mathematically).

re: Fast Facts -- What Is the Comparable Index (CI)?

da3hoss — Wed, 29 Jul 2009 22:28:56 GMT

I'll stick with performance, conformation and a little line breeding (oops, I forget, in TB's it's all inbreeding) and the tail-female line top and bottom...my 4 stallions entering their freshman year were (honest) Birdstone, Candy Ride, M'D'oro and Peace Rules...

I also knew Tiznow would be an enormously valuable stud.

All 5 were super bargains in their first year(s).