Richard Ball wrote about Broncho, an army horse who became a showjumper. I think the story is based on Col. Malise Graham and his horse Broncho. Graham rode the veteran charger at Olympia. To the right is a portrait of him, from Country Life, 6th July, 1929. Richard Ball imagined a history for Broncho. The book is sought after now for its wonderful illustrations by G D Armour, who also illustrated Penny Farthing, the story of a colt and his progress in the racing world.
Finding the books: the limited edition of Broncho is very expensive: reasonable reprints with dustjackets are usually reasonably priced. Penny Farthing is generally more expensive than the run of Broncho copies, though not as expensive as the limited edition.