The X chromosome (female genetic material) is possibly the most important factor in producing above average successful racehorses. It takes two X chromosomes to produce a filly. It takes one X chromosome and one Y chromosome to produce a colt. The X chromosome carries the X Factor genetic material to produce a larger heart that results in a more successful racehorse. By concentrating on the X chromosome (female genetic contribution to a breeding program), selecting for the X Factor which follows certain lines of racehorses, you can increase the success of a race breeding program. To become further educated on the X Factor, read Marianna Haun's two books, The X Factor and Understanding the Power of the X Factor.

The RimRock Ranch breeding program has been based on the importance of the female in a pedigree. We currently have in our broodmare band, three World Champion race mares, six Medallion Winners or Regional Champions, and nine daughters, dams or sisters to Champion racehorses.  With this many brilliant, successful race mares in our broodmare band, we are trying to concentrate the X Factor (large heart) to produce a more successful racehorse.

The X Factor is not the only genetic link to be able to produce an above average successful racehorse. Balance and engineering of the race prospect are also very important. We are constantly striving to produce the best balanced race prospect through the use of Computer Horse Breeders from Colbert, Oklahoma. Our above average success can be attributed to the help they have given us in our breeding program as to predictability of producing the best balanced individual for a particular mating. Combining the best balance possible, the X Factor (large heart) and solid rave production in the pedigree are the keys to our successful race breeding program.