I think the 'safety precaution' may have been the strap attached to something over the roller? I.e may have prevented a fall completely down onto the moving belt?
I wouldn't like it (similarly to how I don't like horse walkers) for an animal of mine of avoidable but the video in OP's link didn't, to me, look like a horse in as much stress as most of the dressage videos HHO members post. Not vastly happy looking, and yes, working, but didn't see heaps of fear or any visible discomfort.
E T Add: would expect this to be acceptable for veterinary or (human) training/education purposes. Would be less pleased if this was done for public entertainment.
I'd not put mine on one but the horse didn't look stressed or over stretched to me, quite the opposite really, they are clearly used to being on a treadmill.
I agree, but those machines scare the hell out of me - and the idea that people are allowed to suddenly stand up in the horse's eyeline and take flash photographs - OMG!
I think there's possibly more to why this horse is on a treadmill and looking like one that's been on it a few times and that people were possibly there to see gaits as a secondary reason.
The main thing I didn't like was the straps from the head collar to a fixed point. Horrendous pressure and very unnatural stress on his neck?! We had a treadmill years ago when I worked for a race horse breeder. The horses were not tied in that manner and would pace themselves ie no danger of them out running it, we would just hold their lead rope. They also really liked it where as that horse looked like it didn't!