The wrangler provides spare horses during roundup, when cowboys change mounts 3 to 4 times a day.
Cattle are still rounded up and brought in off the range in the late summer and fall, with breeding stock sorted and moved to winter pasture, and animals for sale selected for shipping to feedlots.
In both historical and modern times, the necessity of rounding up cattle from the open range is a job primarily performed by a cowboy mounted on a horse.
The terrain as well as unpredictable behavior of cattle render motorized vehicles virtually useless for rounding up and herding.
In modern times, the remuda may be housed in corrals at the trailhead or gathering site, though historically, and in remote areas in modern times where there are few or no corrals, the herd would be kept loose on the range, under the charge of people called wranglers, whose exclusive job was to manage the horse herd.
The horses had been trained sufficiently to accept even the minimal confinement of a rope corral and not test the fence.