By 1842, many emigrants favored oxen—castrated bulls (males) of the genus "Bos" (cattle), generally over four years old—as the best animal to pull wagons, because they were docile, generally healthy, and able to continue moving in difficult conditions such as mud and snow. Oxen could also survive on prairie grasses and sage, unlike horses, who had to be fed. Moreover, oxen were less expensive to purchase and maintain than horses. Oxen also could stand idle for long periods without suffering damage to the feet and legs. Oxen were trained by leading, the use of a whip or goad, and the use of oral commands (such as "Gee" (right), "Haw" (left), and "Whoa" (stop)). Two oxen were typically yoked together at the neck or head; the left ox was referred to as the "near" or "nigh" ox, and the right ox as the "off" ox. While no reins, bits, or halters were needed, the trainer had to be forceful. Oxen typically traveled at a steady pace up to two miles an hour.