My employer has Highland cattle, Suffolk sheep, and Highland ponies/part breds. My neighbour has Clydesdale horses. I have used their livestock trailers to move all the above.
As Dave says, you can get all the equipment for them....such as partitions and breast bars, etc..
They have a metal floor with those raised patterns for grip. We have transported shod horses in them, with and without straw, and have not had any injuries/accidents.
I like them because they have the opening slats along the side, allowing for plenty of ventilation in hot weather.
The ramps are substantial, and the guide gates are handy when loading foals. You can get a transverse partition (fixes onto front of trailer when not in use) which allow two foals to be travelled at the front, seperately from their dams, if needs be, which is handy when speaning foals. We have had two mares and their foals in one when travelling to stud, with plenty of room.
There is ample space inside to turn a horse around if it's wary of backing out.
They are very stable when towed by a long wheel base vehicle, empty and loaded, and are fairly light weight by comparison to some horse trailers.
Remember there is a minimum height restriction if you are travelling equines.