The first batch of outward-bound UK passenger lists will be available at findmypast.com on Wednesday, covering the years 1890-1900.
In one, the names of a dozen American cowboys returning Stateside on a liner, the Alexander Elder, from London to Philadelphia, are written in a careful copperplate hand.Update: No sooner had I posted this than ancestorsonboard.com went live with its search interface. I guess it must be Wednesday already.
Between 1875 and 1914, hundreds of cattleships brought livestock on one-way trips from American ranches to British markets and the animals needed handlers, who often went back on board more luxurious vessels than those on which they arrived. [Link]