the world > animals > mammals > group Ungulata (hoofed) > group Ruminantia (sheep, goats, cows, etc.) > bos taurus or ox > [noun] > oxen or cattle > used for riding
1785 G. Forster tr. A. Sparrman I. Contents p. xxxiii Saddle-oxen.
1824 W. J. Burchell Index, at Oxen Saddle Oxen: their rate of travelling.
1961 H. E. Mautner vi. 95 We now have a reliable Indio who carries the mail on his saddle-ox.