Complex sentence: He also led the juvenile (two-year-old) sire list a record six times; before Secretariat's Triple Crown run, Bold Ruler was often categorized as a sire of precocious juveniles that lacked stamina or did not train on past age two.
Split into simpler sentences: He also led the juvenile (two-year-old) sire list a record six times. Before Secretariat's Triple Crown run, Bold Ruler was often categorized as a sire of precocious juveniles that lacked stamina or did not train on past age two.