Over 60 years ago I remember reading a book by Margaret Cabell Self, sorry I don’t remember which book, where she said that ALL her horses had different summer and winter personalities.
Her riding school was in Maine so the differences between the seasons might be more clear, as in there is no doubt that it is cold and could stay cold for months. I always remembered that and when I got my own horses I kept it in mind, that I might have a few weeks at the beginning of cold weather where the horse and I might have to renegotiate what is acceptable behavior, from both of us.
Even though I live in NC where the difference between summer and winter are a lot less than in Maine in the 1950s and 1960s.
I have no idea of how our current global climate change will affect this. During the winter if we have a week or two of warm weather and then the polar vortex comes to visit us, will we have several of these behavior changes during the winter? First–hey its winter, then–hey, is it spring yet, to oh no, winter is back with a vengeance!