Complex sentence: By 1890, Madden realized that Thoroughbred racing was attracting higher purse values than harness racing and he gradually shifted his interests, but he still owned and trained a few Standardbreds into the 1900s.
Split into simpler sentences: By 1890, Madden realized that Thoroughbred racing was attracting higher purse values than harness racing, and he gradually shifted his interests. He still owned and trained a few Standardbreds into the 1900s.