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In an article for Thoroughbred Daily News last Wednesday, Bill Oppenheim fell upon the topic of inbreeding to Northern Dancer and evaluated the practice in terms of his APEX runner database. He studied horses inbred to Northern Dancer in the male line and broodmare sire line

as a percentage of all Northern Dancer-line sired A Runners, by year foaled, 1996-2005. That percentage increased from 13.2 percent among 380 Northern Dancer-line sired A Runners foaled in 1996 to 22.4 percent of the 566 Northern Dancer-line sired A Runners foaled in 2004, and 22.7 percent of the 409 Northern Dancer-line sired A Runners of 2005 (including just three-year-olds by the end of 2008, so the number of 2005-foaled A Runners will have increased significantly by the end of 2009).

Then Oppenheim evaluated the A runners inbred to Northern Dancer as a percentage of all A runners in his database. He wrote: “That percentage has increased from 4.3 percent (50) of the 1,151 A Runners foaled in 1996 to 9.3 percent (127) of the 1,371 A Runners foaled in 2004, and 9.6 percent (93) of the 967 A Runners (through the end of 2008) foaled in 2005.”

Coincidentally, in the current issue of International Thoroughbred, David Dink has authored an article and companion study of 7,206 horses from weanling, yearling, and 2-year-old sales from 1999 through 2002, which is a slightly older population than Oppenheim’s. Dink’s massive study of this moderately elite group (sales horses are better than overall breed norms) yielded 13.28 percent inbred to Northern Dancer through any line in the pedigree. Part 1 of this study, with discussion of the statistics and their implications, is in the current issue of International Thoroughbred, and Part 2 of this study is planned for the next issue of the magazine.

Dink’s study answers one of the questions posed by Oppenheim in his article last week: “Is Northern Dancer over Northern Dancer 9 or 10 percent of the whole population?” From the data mined by Dink, the answer is an unequivocal “yes.”

This is an increasing trend as both of these statistical approaches show, and one of the corollaries to this rising line of incidence is that more and more lesser horses will be mated along these lines, resulting in less success for this type of cross. But importantly, it is an approach that breeders and advisers respond to and consider seriously.

Dink said, “One of the reasons I undertook this study was that when you put statistics in terms of inbreeding, people will pay attention. If, on the other hand, I had evaluated the numbers in terms of positions of horses in pedigrees, they just yawn.”

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