In Thoroughbred racing and breeding, the broodmare sire—also called the dam’s sire—is the stallion that fathered a horse’s dam. In other words, it is the horse’s maternal grandfather, and his genetic influence enters the pedigree through the female line. Breeders and bloodstock analysts pay close attention to broodmare sires because certain stallions consistently produce daughters that become exceptional producers themselves, boosting the value and racing potential of their grand-foals.