Speed gene*

Known as MSTN, the gene regulates myostatin, a protein that controls muscle cell production. There are three different variants of the myostatin gene a horse can inherit: TT, CC and CT. Horses with the TT version develop muscles later in life. Horses with the CC version develop their muscles earlier. Horses with the myostatin gene combination designated as C/C are better suited to fast, short races; those with the C/T variation tend to compete better over middle distances; and T/T animals have more stamina and thus are better suited to long distances.