Complex sentence: In 2012, Wise Dan won five more races, including Woodbine Mile, Shadwell Turf Mile Stakes, and the Breeders' Cup Mile: by autumn he was the most highly rated active racehorse in North America.
Split into simpler sentences: In 2012, Wise Dan won five more races, including Woodbine Mile, Shadwell Turf Mile Stakes, and Breeders' Cup Mile. By autumn, he was the most highly rated active racehorse in North America.