It is VERY difficult to get agricultural land changed to residential use. A livery yard is not residential use so that is not relevant.
Was the '5 bed' on agricultural land?
Land with planning permission for residential use is worth at least
10 x what it is as agricultural land.
You can put a static caravan on the land but without permission for residential use you can not live permanently in it. But you can use it as temporary accommodation while you tend to your animals.
You really do need a professional agent working on getting planning permission not just a post on a web site such as this.