Blow The Horn is the only runner so far out of Halteclere (Durandal), who won four races in Japan. She is a full sister to the 11-time winner Speed Revival and a half-sister to the seven-time winner Desert Snake (Black Tide), placed in the Listed Betelgeuse Stakes.

Second dam Joy Assertaine (Forty Niner) won three races and is the dam of the Listed-placed Desert Snake. She is a half-sister to Jo Yamato (Symboli Rudolf), a winner who was second at Listed level.

Third dam Assertaine (Assert) won at three and is a half-sister to Go For Wand (Deputy Minister), champion filly in the US and a multiple Grade 1 winner, and to the Grade 2 winners Dance Spell and Discorama, both by Northern Dancer and both placed several times at the highest level; Dance Spell also became a sire.

The fourth dam Obeah (Cyane) won two Grade 1 races.