If the definition of an inbred horse is one that has at least one duplicated ancestor between the parents within four generations, then an outcrossed one has no closely duplicated ancestors at all. The majority of the breed is outcrossed, which should relieve the fear that the Thoroughbred is overrun with irresponsible and debilitating inbreeding. It is not.
The limited study in last month’s review of inbreeding used winners of the Triple Crown races and 3-year-old male division champions since 2000. Of that very small group of 39 individuals, 15 were inbred (38.5%) and 24 were outcrossed (61.5%).