We have both Spring and Fall calving groups.
While the heat may be an issue for the very earliest of those 'Fall' calves, it's still nothing like the problems we can encounter with snow/mud, etc. in the 'Spring' group... although we shoot for March-April calves, some invariably come in Feb.
I'd a whole lot rather deal with pushing a calf to the shade than having to bring one in to the house to warm up after its dam pushed it out into 6" (or 18") of snow, and it melted down to the ground, with its legs sticking up in the air, or the calf can't find the udder, 'cause it's down in the snow.