hi, i used to live there (near enough) and we kept our horses in daglingworth, which is close to ciren. it has changed ALOT since i was there- it was a polo yard with about 25 horses plus our 7 and 2 ponies.. now i think its more of a business... heres the link: http://www.greenhillequitation.com/
it has lovely hacking- out of the back of the yard, along a track and into cirencester park
have you looked at the google link?
also there was someone else we kept our horses aat, a bit further away and he was called richard knight- not sure if they have a website as was us and their horses but again great hacking, gallops and point to point course!