With a trailer, generally more air moving through
it is better than less. Then you don't have problems with dust or ammonia,
and the horse stays cooler. I wouldn't worry too much about the cold,
unless you plan to haul long distances in sub-freezing weather. Last
winter I hauled a couple of horses from Nebraska to central Texas in 20-30
degree weather (and blowing snow) in an open trailer without any problems (I
realize these are not the best conditions, but I didn't have much choice).
Neither horse was blanketed, and both did just fine. I wouldn't
recommend this kind of hauling on a regular basis, but just used it as an
example. A horse's idea of confort differs greatly from our own, and my
horses always loaded better and hauled better in trailers with open sides.
Anyone else have this experience?