Degree of Inbreeding

When I started this blog more than five years ago I posted lots of statistics about inbreeding. Then I got off that subject and moved on to other topics.

Recently I decided to revisit this whole concept of inbreeding. All my previous posts on the subject were based on sales foals of 2003-2007. I wanted to see how things may or may not have changed with sales foals of 2008-2111.

I also wanted to do things a little bit differently. The very definition of inbreeding is somewhat amorphous. Some people think that any duplication 4×4 or closer constitutes inbreeding. Some people think 5×5 or closer (mainly because almost all available pedigrees include at least five generations now).

After some consideration I have decided to side with the former. For purposes of the posts to follow only duplications 4×4 or closer will be considered inbreeding.

All my research has tended to show that the positive “influence” of ancestors recedes much more rapidly than most people think. Duplications in the fifth generation are pretty much superfluous. I have my doubts about duplications in the fourth generation having much positive influence as well but am willing to give them the benefit of the doubt.

Most of the breed is neither inbred (by the 4×4 or closer definition) nor outcrossed (lacking any duplications at all between sire and dam within five generations). American Pharoah is a good example. He is 5×5 to Northern Dancer, and that is the only duplication in his pedigree within five generations.

American Pharoah is neither inbred nor outcrossed. I have decided to call this pedigree characteristic NINO (neither inbred nor outcrossed).

Secretariat is a good example of an outcross. He has no duplications whatsoever within five generations of his pedigree. Many outcrosses do have duplications within five generations of their pedigrees, just not between their sires and dams. Their sire may be inbred within four generations. Their dam may be inbred (ditto). Both sire and dam may be inbred (ditto). The defining factor is that an outcross has no duplications between sire and dam within five generations.

So the first order of business is to determine how the distribution of these three groups has changed from sales foals of 2003-2007 to sales foals of 2008-2111. The chart below summarizes the results.

Category               2003-2007 Foals      %       2008-2111 Foals      %         Change

4×4 or Closer               21,988                31.09             15,163             33.28        +7%

NINO                              31,680                44.80            20,617             45.25       +1%

Outcrossed                   17,046                24.11               9,782             21.47      –9%

Totals                             70,714                100.00           45,562          100.00

The results above are not at all surprising. The 4×4 or closer group is up 7% from 2003-2007 to 2008-2111. The outcrossed group is down 9% over the same time range. The NINO group is up slightly (1%). The breed is getting more inbred every year.

What might be surprising is that the degree of change is fairly small. The statement that the breed is getting more inbred is usually accompanied by wailing and gnashing of teeth. All sorts of woes are attributed to this trend.

I do not dispute that this trend is happening by any means. I am just not 100% positive that it is a totally bad thing. Foolosophically, I do not like it that the breed is becoming more and more uniform in terms of its pedigrees. A lot of diversity is being lost.

The main driving factor behind this is that more and more people are breeding to sell and fewer and fewer people are breeding to race. The former can not afford the luxury of nonconformity. The latter can somewhat.

Foolosophically, I am all in favor of nonconformity. But I am not 100% positive that this trend toward more uniformity in pedigrees is a totally bad thing. It might be. It might not be.

Enough foolosophizing. The table below examines the prices for these three groups for sales foals of 2008-2111.

Category                     Foals          Average          Maverage          Price Index

4×4 or Closer             15,163         $53,040              165.62                    1.08

NINO                            20,617        $45,208              152.24                    0.99

Outcrossed                  9,782         $38,703              139.72                    0.91

To review, the overall average for all 45,562 sales foals of 2008-2111 was $46,418, and the overall maverage was 154.0 (Price Index of 1.00). The 4×4 or closer group was above those benchmarks on all three counts. The NINO group was slightly below on all three counts. The outcrossed group was farther below on all three counts.

Now let us examine the racetrack results for these three groups. APPPSW stands for average Performance Points per stakes winner, a measure of the quality of stakes winners involved (the average now being 687).

Category                   Foals     Stakes Winners     %     APPPSW      PPI (Result)

4×4 or Closer           15,163               539                3.55        713                 1.10

NINO                          20,617              719               3.49       699                1.06

Outcrossed                 9,782              268               2.74       599                0.71

The results pretty much mirror the prices, 4×4 or closer best at 1.10, NINO next at 1.06, and outcrossed a distant trailer at 0.71.

A comparison of the prices to the results might be illuminating. The chart below attempts to do so.

Category            Foals          Price Index          PPI (Result)          Difference

4×4 or Closer    15,163                1.08                      1.10                          +0.02

NINO                   20,617               0.99                     1.06                         +0.07

Outcrossed         9,782                0.91                      0.71                       –0.20

This chart tells a somewhat different tale. The NINO group was positive at +0.07, the 4×4 or closer group was only slightly positive at +0.02, and the outcrossed group was very negative at –0.20. So the NINO group was the best value. The 4×4 or closer group was only slightly better than expected. The outcrossed group was much worse than expected.

I mentioned earlier that there were four types of outcrossed groups. None of them were any good at all. The Secretariat group (total outcrosses) had a price of 0.90 and a result of 0.70. The sire-inbred group had a price of 0.88 and a result of 0.67. The dam-inbred group had a price of 0.94 and a result of 0.82. The both-parents-inbred group was worst of all, with a price of 0.94 and a result of 0.60.

So inbreeding 4×4 or closer was only slightly effective. The best value was to be found among foals who were neither inbred nor outcrossed (NINO).

Of course the effectiveness of inbreeding 4×4 or closer is going to depend on what name is duplicated. Some names will be good. Some names will be bad. Rest assured that that this factor will be examined in a later post.

One of the reasons inbreeding 4×4 or closer was only slightly effective was because inbreeding 3×3 or closer (included in the above) was particularly abominable. Those details will be forthcoming in my next post.





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