It depends on the horse but up to 55mph
The cast of Riderless Horse - 2000 includes: Francis Dobrisky as Horse Handler
Riderless Horse - 2000 was released on: USA: 9 June 2000 (TV premiere)
Buttermilk
A horse that loses its rider is disqualified.
Black Jack
Black Jack
Black Jack
http://en.wikipedia.org/wiki/Riderless_horse
34mph
105-110 mph
around 25 to 38 mph !
A horse has has a top speed of about 45-50 mph