I have been visiting the MK for the past 34 and a half years of my life and I have NEVER EVER seen horse drawn carriages transporting guests like the one seen on that photo, except during parade performances or during special private events, like weddings at the castle forecourt. You must be confusing your information with the horse-drawn trolley carts that travel on the track in the center of the street... and yes, those have been there since day 1 at the MK. But not the one seen on the photo...which I find totally odd. Furthermore... I have never seen anyone pay to ride the trolley ever except in the days when the ABCDE tickets existed.