I received the following comment on my post about racing class of dams from a little over a year ago.
“I’m quite convinced on your general refutation (or perhaps debunking) of close inbreeding generally. I do wonder if there is a case in which it might matter. Suppose you compare to individuals to have similarly elite racing class, one is an outcross and one is close inbreed. Do they differ in ability to produce foals of high class? This normalizes racing class and focuses on homogeneity. My hypothesis would be that the inbreeds outproduce but have no idea if that would be born out by the statistics.”
The above is a fair question, and I decided to explore it a bit. Of the 45,562 sales foals of 2008-2111, 6,659 were out of stakes winners. Of those 6,659 foals, only 150 (about 2.25%) were out of mares inbred 3×3 or closer. (The reader specified “close” inbreeding.)
The remaining 6,509 foals were out of mares not inbred 3×3 or closer. Call the former group DI (for dam inbred) and the latter group DNI (for dam not inbred). Below are the prices for the two groups.
Group Foals Average Maverage Price Index
DI 150 $68,051 208.15 1.35
DNI 6,509 $85,442 222.99 1.45
Totals 6,659 $85,050 222.66 1.45
As you can see, there is quite a bit of difference between the two groups in terms of prices. The DNI group was more expensive than the DI group ($85,442 to $68,051 by average, 222.99 to 208.15 by maverage, and 1.45 to 1.35 by Price Index).
Below are the racetrack results for the two groups. APPPSW stands for average Performance Points per stakes winner, a measure of the quality of stakes winners involved, with the benchmark now being 693.
Group Foals Stakes Winners % APPPSW PPI (Result)
DI 150 11 7.33 649 2.04
DNI 6,509 306 4.70 849 1.71
Totals 6,659 317 4.76 841 1.71
The DI group was much better than the DNI group by percentage of stakes winners from foals (7.33% to 4.70%). But the DNI group was better than the DI group by APPPSW (849 to 649). Taking both quantity and quality of stakes winners into account, the DI group was decisively better than the NDI group (2.04 to 1.71) despite its lower prices.
So the DI group sold for prices about 35% above average and produced results about 104% above average (an improvement of 0.69). The NDI group sold for prices about 45% above average and produced results about 71% above average (an improvement of 0.26).
So, yes, the DI group was definitely better than the NDI group, lending credence to the theory that inbred (3×3 or closer) dams make better producers than dams not inbred that closely.
At least among dams who were stakes winners. Just for grins I also tracked foals out of mares inbred 3×3 or closer who were NOT stakes winners. There were 1,282 such foals, and their prices are summarized below.
Dams Inbred 3×3 or Closer
Category Foals Average Maverage Price Index
Not SWs 1,282 $43,608 145.71 0.95
SWs 150 $68,051 208.15 1.35
Totals 1,432 $46,168 152.25 0.99
The overall average for all 45,562 foals was $46,418, and the overall maverage was 154.0. The 1,432 foals out of mares inbred 3×3 or closer were just below those benchmarks by both average ($46,168) and maverage (152.25, which corresponds to a Price Index of 0.99). The prices for the 150 foals out of mares who were stakes winners and also inbred 3×3 or closer were significantly higher, of course.
Below are the results for the three groups.
Category Foals Stakes Winners % APPPSW PPI (Result)
Not SWs 1,282 34 2.65% 719 0.82
SWs 150 11 7.33% 649 2.04
Totals 1,432 45 3.14% 702 0.94
The 1,432 foals (both stakes winners and not) sold for a price of 0.99 (about 1% below average) and achieved a result of 0.94 (about 6% below average). They were slight underachievers.
The 150 foals out of stakes winners sold for a price of 1.35 (about 35% above average) and achieved a result of 2.04 (about 104% above average). They were definite overachievers.
The 1,282 foals out of mares who were not stakes winners sold for a price of 0.95 (about 5% below average) and achieved a result of 0.82 (about 18% below average). They were more definite underachievers.
The point is that just because mares who were stakes winners and inbred 3×3 or closer achieved much better results than their prices warranted, be wary of theorizing too broadly from that. What works for stakes winners may not necessarily work for mares who were not stakes winners. In this case it did NOT work for mares who were NOT stakes winners. Even with the fantastic results from those 150 foals, the overall results for all 1,432 foals were still slightly negative.
The more important point could be that close inbreeding might indeed intensify the characteristics (both good and bad) of the mare in question. Inbreeding works both ways, in other words, intensifying both the good and the bad.
But it does appear that foals out of stakes winners who are inbred 3×3 or closer do outperform their prices rather significantly. I would not have believed it if I had not done all the research and number crunching myself. You learn something new every day.