Conversation so far:
What did Secretariat accomplish at the Kentucky Derby?
No other horse had won the Derby in less than 2 minutes before, and it would not be accomplished again until Monarchos ran the race in 1:59.97 in 2001.
What else did Secretariat accomplish?
At age two, Secretariat finished fourth in his 1972 debut in a maiden race, but then won seven of his remaining eight starts, including five stakes victories.

Question: When did the horse enter the Kentucky Derby?
Self-contained rewrite: When did Secretariat enter the Kentucky Derby?