Complex sentence: Under William Woodward, Sr. the farm produced some of the greatest thoroughbred racehorses in the United States including Gallant Fox and Omaha, the only father and son horses to ever win the U.S. Triple Crown of Thoroughbred Racing.
Split into simpler sentences: Under William Woodward, Sr. the farm produced some of the greatest thoroughbred racehorses in the United States. Some of Woodward's most famous horses were Gallant Fox and Omaha, the only father and son horses to ever win the U.S. Triple Crown of Thoroughbred Racing.