Two cases of Sherlock Holmes, (fictitiously) chronicled by his faithful companion Dr. John Watson, involve horse racing.

In Silver Blaze, Holmes and Watson investigate the murder of trainer John Straker and the disappearance of Silver Blaze (5yo by Isonomy), the favorite for the Wessex Cup. The short story, released in 1892, is part of the Memoirs of Sherlock Holmes. 

Shoscombe Old Place is the estate of Lady Beatrice Falder, a widow who lives with her bother Sir Robert Norberton, a notorious gambler with substantial debts. Their racing stable includes Shoscombe Prince, a contender for the Derby. Trainer John Mason makes a call on Holmes to have him investigate a handful of strange happenings at the estate. Shoscombe Old Place, released in 1927, was the last published Holmes case by Conan Doyle and is part of the Case Book of Sherlock Holmes.

Both stories were brilliantly dramatized by Grenada Television, starring Jeremy Brett as Sherlock Holmes. In Shoscombe Old Place, one of the minor characters is played a young Jude Law. Law plays Dr. Watson in the upcoming Sherlock Holmes movie opposite Robert Downey Jr as Holmes.