You can now test your racehorses for speed through Equinome. They have developed a genetic test for Thoroughbreds for the C:C (short), C:T (middle) and T:T (long) genes. C:C -likely to be a fast, early maturing horse that performs well as a two-year-old. Average best distance – 6.5 f (1300 m) C:T -mixture of speed [...]
Here is an abstract of research from Northern Arizona University finding that stallions were faster than both mares and geldings. Looking at the results for Thoroughbred, the stallions were lengths ahead of the mares at the 1600m (or less) races and there was twice as much difference between them at races over 1600m. Do racehorses [...]