Agricultural occupancy conditions can have varied forms of wording but they always relate to the
employment of one or more residents of the property. This must be in agriculture, which basically relates to
farming for food production (although growing crops for non-food purposes, such as linseed, would also qualify).
There is no need for any involvement with livestock; arable farming still counts as 'agriculture'.
Working with horses would only qualify as 'agricultural employment' if, say, it was on a 'heritage' farm (where the horses were used to pull ploughs) or on a farm where the horses were being bred for their meat.
Some agricultural occupancy restrictions might extend the permissible range of occupations to include such things as forestry. Additionally, there are usually provisions permitting agricultural workers who retire (or the widows of agricultural workers) to continue living in the property. See the second half of this page:
http://www.tiebreaker.co.uk/
Chris