1861 32 ii. 131 Simonides, when offered a small price for an ode in honor of a victory in a mule race, contemptuously calls the successful animals half-asses.
1916 W. S. Churchill Let. 17 Jan. in W. S. Churchill & C. S. Churchill (1999) vii. 155 They were most amusing sports—mule races, pillow fights, obstacle races etc.
2000 (Nexis) 3 Aug. e1 Now, mule races attract the same purses and betting handles as quarter horses, Appaloosas and Arabians.