I
it is the same - it is a conveyance
Indeed... The theft act 1968 sec(12,7) states that "conveyance" will mean any conveyance for carraige of persons by land, water, or air.
However a Horse is not a conveyance under the act.
Theft (or TWOC for that matter) of a horse is of course against the Horse Russling act of 1864 and punishable by a "good 'ole whoopin" and a trip, feet first to boot hill...!