TT

From HelpWiki

TT stands for Time Trials. This is the lowest grade a horse can start out with in the racing register. A horse with this grade level means that it hasn't been tried for racing potential. Once it's got a few races under it's belt it will move on to the next grade which is starters races or SR. If you breed from two other horses instead of creating it from the store then you have less of a chance of getting a foal at this race level.