cattle would have to be herded from the ranch in the middle of no-where, to a major city or railroad to be sold, killed, packed, and shipped off to cities in the east and west, where cattle were more rare.
during hearding season, the cattle would have to be herded throught the same obsticles that the ranchers had to face when they moved out west. Rivers, for example, and other challenges like preditors and even bad rain storms and thunder and lightning claimed the lives of many of the cattle
Often times, ranchers and other travelers would pass by a large herd of bison in the praries. these people would hunt the bison herds for sport or pelt alone. the extreme hunting of the bison is what lead to the almost endangerment of the animal.