This video was taken of a trailer traveling at about 70 MPH on Route 3 North in Massachusetts. Letting horses stick their heads out of the windows on a highway at speed is a terrible idea. Your horse could be injured by debris thrown up into their faces, or even hit by a passing semi.
They can still get air if you use the window screens!
Please trailer your horse safely.
That’s not a real good idea, the wind in their eyes must’ve been uncomfortable. Plus, there are some truly stupid people out there, flicking cigarettes out windows, etc. My Granddad had an old open-style stock trailer, the kind normally used to move horses around large ranches. When he bought a pony for all the grandkids and hauled it from El Paso to Marfa, he used this trailer. We had to pull over at one point as some “good old boys” had decided to amuse themselves by whipping empty beer bottles at the pony. But he did have goggles on to protect his eyes from wind and dust, gravel, etc.
Bugs and debris would be the most probable danger. As any motorcycle rider will tell you, a bumble bee at 70 mph feels like a boulder! A bug hitting the horse’s eye could cause a lot of damage at high speeds.