A 3,5 tonne box has a payload of 1.2 for the very lightest modern ones down to much less
One horse or two ponies, even if the stalls will take two hroses, it will be overwieght, tack, hay, water , kit, passenger etc all have ot be included, and allow more thna a weightape reading for the horse. Mine was almost 100 kilos more on a vet weighing stall than a tape made him!