Complex sentence: Retired to stud in 1974, Secretariat ultimately became notable as a broodmare sire, as despite the success of some of his progeny on the track, he was most influential though through his daughters.
Split into simpler sentences: Retired to stud in 1974, Secretariat ultimately became notable as a broodmare sire. Despite the success of some of his progeny on the track, he was most influential though through his daughters.