A Blast From the Past

Performance of North American-Bred Foals of 1983 by Degree of Inbreeding

Inbreeding        Foals      Stakes Winners      %       Graded Stakes Winners      %

3×3 or closer     1,351                25                 1.85                         6                       0.44

4×3 or closer     3,820               89                 2.33                       24                       0.63

4×4                     7,429              279                3.76                        48                       0.65

5×5 or closer   25,614              804                3.14                      165                      0.64

Outcrossed       7,429               186                2.50                        38                      0.51

Totals              45,643            1,383               3.03                       281                     0.62

This chart was published back in the early 1990s. I compiled it in order to settle a controversy. Many people back then insisted that close inbreeding was good (incest is best!!!!!) and that the closer the inbreeding, the better the results. Many other people insisted that inbreeding was bad and that outcrossing produced the best results.

Before proceeding I should explain that these North American-bred named foals of 1983 were classified by their CLOSEST inbreeding. I was looking only at the CLOSEST duplication in each foal. So 3×3 or closer was comprised of 1×2, 2×1, 2×2, 2×3, 3×2, and 3×3. The 4×3 or closer group was comprised of 2×4, 4×2, 3×4, and 4×3. The 5×5 or closer group was comprised of 2×5, 5×2, 3×5, 5×3, 4×5, 5×4, and 5×5.

The controversy was settled by declaring a pox on both of your houses. Neither group of claimants was correct. Close inbreeding was not any good at all. Total outcrossing was not good either (though better than close inbreeding).

The best results clearly belonged to the 4×4 group (3.76% stakes winners from foals and 0.65% graded stakes winners from foals, compared to the breed norms of 3.03% and 0.62% respectively).

Graded stakes winners were not nearly as affected by degree of inbreeding as total stakes winners. The three middle groups posted results of 0.63%, 0.65%, and 0.64%, with 3×3 or closer at 0.44% and outcrossed at 0.51%.

Total stakes winners were more affected by degree of inbreeding. The same three middle groups posted results of 2.33%, 3.76%, and 3.14%, with 3×3 or closer at 1.85% and outcrossed at 2.50%.

The only two problems with this study were that I did not take into account the QUALITY of the pedigrees involved nor the QUALITY of the stakes winners (other than differentiating graded stakes winners from ordinary stakes winners).

Having solved those two problems since then, I thought it would be interesting to see how sales foals of 2003-2007 compare to North American-bred named foals of 1983 in terms of their distribution. Hence the chart below.

Named Foals of 1983                                  Sales Foals of 2003-2007

Degree of Inbreeding       Foals       %       Foals        %        Change

3×3 or closer                      1,351    2.96     2,517      3.56       +20%

4×3 or closer                      3,820    8.37     9,028    12.77      +53%

4×4                                     7,429    16.28   10,443    14.77      –9%

5×5 or closer                   25,614    56.12   31,680    44.80     –8%

Outcrossed                       7,429     16.28    8,451      11.95     –27%

Other Outcross                                            8,595      12.15

Totals                               45,643    100.00  70,714   100.00

The percentage of 3×3 or closer rose from 2.96% in 1983 to 3.56% in 2003-2007 (a 20% increase). The percentage of 4×3 or closer rose from 8.37% in 1983 to 12.77% in 2003-2007 (a 53% increase). On the other end of the spectrum, the percentage of outcrossed foals dropped from 16.28% in 1983 to 11.95% in 2003-2007 (a decrease of 27%).

All of which tends to support the hypothesis that the breed as a whole is more inbred now than it was 20+ years ago. Some of this change might be attributed to the different natures of the samples. Sales foals are generally better foals than all foals. They have better overall pedigrees.  Nevertheless, the changes over the years appear to be pretty significant.

The comparisons between the 4×4 and 5×5 or closer groups are not really valid. Because I classified the foals somewhat differently for foals of 1983 than for sales foals of 2003-2007. The comparison for the outcrossed group is valid because both groups were comprised of foals with no duplications whatsoever within five generations.

The difference is for 1983 foals I counted the incidental inbreds (foals with duplications within sire or dam but not BETWEEN sire and dam) as inbred. For sales foals of 2003-2007 I counted them as other outcrosses. (See earlier post on outcrosses for more discussion and explanation.)

Most of those 8,595 sales foals of 2003-2007 I counted as other outcrosses would have fallen into the 4×4 and 5×5 or closer groups among foals of 1983. If you combine the 4×4 and 5×5 or closer groups in 1983, you get 33,043 foals (72.39% of the total). If you combine the 4×4, 5×5 or closer, and other outcross groups in 2003-2007, you get 50,718 foals (71.72% of the total).

It seems safe to conclude that there has not been much change over the years in these groups. The biggest change is that closely inbred foals have increased and totally outcrossed foals have decreased.

All that is very interesting, but it is only the prologue, so to speak. Next time around I will show and discuss prices and results for sales foals of 2003-2007 by degree of inbreeding.

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One Response to A Blast From the Past

  1. Pingback: Degree of Inbreeding | Boojum's Bonanza

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