This morning the brave and valiant Barbaro was allowed to rest from his great trials, trials in which he showed more heart and patience and trust than any of his breed before him. His shattered leg was healed, but the laminitis had spread. He could no longer continue his fight without increasing pain, and so his owners made the ultimate decision to let him go.
RIP, Barbaro. He's gone to the Racetrack Eternal, where he can try his speed with the best who have gone before.
"The engine has broken down," said the Master solemnly.
"No," sobbed the Mistress, wiser than he. "The engineer has left it."
-- from memory, Further Adventures of Lad by Albert Payson Terhune.