Deuteronomy 22:10

_ _ Thou shalt not plough with an ox and an ass together — Whether this association, like the mixture of seeds, had been dictated by superstitious motives and the prohibition was symbolical, designed to teach a moral lesson (2 Corinthians 6:14), may or may not have been the case. But the prohibition prevented a great inhumanity still occasionally practiced by the poorer sort in Oriental countries. An ox and ass, being of different species and of very different characters, cannot associate comfortably, nor unite cheerfully in drawing a plough or a wagon. The ass being much smaller and his step shorter, there would be an unequal and irregular draft. Besides, the ass, from feeding on coarse and poisonous weeds, has a fetid breath, which its yoke fellow seeks to avoid, not only as poisonous and offensive, but producing leanness, or, if long continued, death; and hence, it has been observed always to hold away its head from the ass and to pull only with one shoulder.