I have never had to think about this before, but yesterday I witnessed someone trying to load a pony into a sheep trailer. Initially I went to see if I could help. I managed to get the little mare to walk up onto the ramp, but as she was standing at the top looking in I realised that there was very little headroom and advised the owners to rethink this. I noticed that they were still trying to load her as I left (had my own livestock to think of) but does anyone know what the required legal height is above a horses head.
I don't know the required legal height, but I too have seen horses in small trailers. Usually they look like farmer types!!! And like you have seen, they always seem to have loading problems. I wounder why!!!
I am sure there is a legal requirement in a horse trailer of around 7' - but that would not be relevant to a stock trailer, which is not necessarily designed to carry horses.