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EQUUS - - Contents - By Deb Bennett, PhD

Even as we cel­e­brate this year's Triple Crown win­ner, it's time to take a hard look at what modern Amer­i­can breed­ing pri­or­i­ties may mean for the fu­ture of the Thor­ough­bred.

Only three years down the pike from Amer­i­can Pharoah, and we have an­other Triple Crown win­ner! Trainer Bob Baf­fert has ex­pressed as much sur­prise as any­one else, but from my per­spec­tive the re­cent win by Jus­tify was not a mere mat­ter of luck. Baf­fert trained both Jus­tify and Amer­i­can Pharoah, and there is no doubt in my mind that he pos­sesses a su­pe­rior con­cept of how to train and con­di­tion Thor­ough­breds for clas­sic dis­tance rac­ing.

In pre­vi­ous ar­ti­cles, we have ex­am­ined sev­eral great race­horses of the past---Man o’ War, Phar Lap and Sec­re­tariat, com­par­ing them in terms of pedi­gree, con­for­ma­tion and gal­lop­ing style to the 2015 Triple Crown cham­pion, Amer­i­can Pharoah (see “Amer­i­can Pharoah and the Triple Crown,” EQUUS 458). Sec­re­tariat, the 1973 Triple Crown win­ner, re­mains the ab­so­lute gold stan­dard for speed in flat-track race­horses, with Man o’ War a close sec­ond (see “Se­crets of Sec­re­tariat’s Speed,” EQUUS 434). This year’s win by Jus­tify pro­vides a fresh op­por­tu­nity to look at trends in Thor­ough­bred breed­ing, vari­a­tion in con­for­ma­tion and the gal­lop­ing biome­chan­ics of fast race­horses.


I hope that any­one in­volved in Thor­ough­bred breed­ing will take note of the pedi­gree analy­ses pre­sented in this ar­ti­cle. Color-coded charts make trends stand out at a glance, and I’m not go­ing to beat around the bush: By any bi­o­log­i­cal mea­sure, the fu­ture of the Thor­ough­bred is in jeop­ardy due to relentless inbreeding. This trend is ev­i­dent across all dis­ci­plines, but it par­tic­u­larly af­flicts flat-track racers.

As the in­creas­ing amount of red in the charts clearly shows, inbreeding is ev­i­dent in ev­ery Triple Crown win­ner and con­tes­tant from about 1975 onward. All con­tes­tants in both the 2015 and 2018 Triple Crowns are sire-line de­scen­dants of a sin­gle horse, Phalaris, foaled in 1913, and all but one de­scend from this horse in dam­sire line as well. Worse, in the 2015 and 2018 fields, 52 per­cent and 46 per­cent re­spec­tively of all the horses who com­peted de­scend in ei­ther sire line or dam­sire line from Mr. Prospec­tor, him­self a dou­ble-Phalaris horse (Raise a Na­tive x Gold Dig­ger). All of the 2015 and 2018 con­tes­tants sired by Mr. Prospec­tor came from Phalar­is­bred mares, cre­at­ing foals in­tensely in­bred to that one sire.

As early as 1966---be­fore the modern era of DNA test­ing---re­searcher Ann T. Bowl­ing uti­lized blood pro­teins to demon­strate that the Thor­ough­bred is the most in­bred of all ma­jor horse breeds and warned of the dele­te­ri­ous ef­fects of unchecked inbreeding. An im­por­tant study re­ported in 2001 by E.P. Cunningham and col­leagues at the Univer­sity of Dublin es­ti­mated an inbreeding co­ef­fi­cient of 12.5 per­cent for the Thor­ough­bred pop­u­la­tion of about 300,000 in­di­vid­u­als world­wide. By con­trast, be­hav­ioral stud­ies on free-rang­ing feral Ca­mar­gue horses and Amer­i­can

mus­tangs have shown that af­ter their first heat, young fe­males nor­mally dis­perse from their natal herd, seek­ing to join a group where they may be closely re­lated to some fe­males but dis­tantly or not at all re­lated to the males. This be­hav­ior nat­u­rally main­tains a low de­gree of inbreeding. In par­al­lel fash­ion, sci­en­tists manag­ing the ge­netic health of cap­tive en­dan­gered species, such as the Prze­wal­ski’s horse, seek to en­sure that at least 90 per­cent of the ge­netic di­ver­sity in the species is main­tained over a 100-year time pe­riod.

For this ar­ti­cle, I an­a­lyzed the pedi­grees not only for Amer­i­can Triple Crown con­tes­tants but also for graded stakes races of sim­i­lar length in other coun­tries, for the Mel­bourne Cup (two miles on turf), for Olympic-cal­iber

Grand Prix jumpers, for the British Grand Na­tional steeple­chase (four miles, 514 yards on turf), and for the gru­el­ing Mary­land Hunt Cup, which is not only four miles long but con­ducted on rolling ter­rain over solid fences up to five feet in height. Shock­ingly, I found “Phalaris creep” in all cat­e­gories, with Grand Prix jumpers---whose ath­letic chal­lenges are the most dif­fer­ent from those of the flat-track racer---the least af­fected (to see more on this anal­y­sis, go to “Inbreeding Across The Board,” Equ­

In­creas­ing creep is ev­i­dent in all cat­e­gories of flat-track rac­ing. Why is this? Fun­da­men­tally, it is be­cause modern race­horse breed­ers are not search­ing for rare al­le­les0 and are not seek­ing the kind of all elic di­ver­sity ev­i­dent in

Jus­tify cap­tures the 2018 Preak­ness Stakes


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