The cowboy mouse is riding his sawhorse across the landscape to round up a herd of mustangs in this pretty good Paul Terry-Van Beuren cartoon from 1927.
In fact, the first half is very good, with some care taken with the animation and a startling early prison scene that I thought originated three years later in MGM'S THE BIG HOUSE -- apparently both that movie and this cartoon lifted it from elsewhere. However, in the second half we get to see some typical Terry shortcuts -- lots of looping to save production costs as well as a retreat to a standard plot, with at least one gag lifted from the first half.