Not a historian but I did grow up on a horse in hot af weather. Long sleeves even in heat for a few reasons: 1 bugs, until you’ve sat on a horse you’ll never realize how many bugs they deal with in life, you do not want to get bit by a horsefly trust me 2 farmers tans suck 3 it’s really not that bad up there even in 100f/38ish c weather 4 you get used to it and the horse is doing most of the work 5 even if you’re not on the horse, you can always roll up the sleeve or unbutton the shirt it’s not like you’re trapped in a long sleeve shirt like it’s welded onto you or anything 6 it only sucks bad when you have to dig fence posts in 100f/38ish c weather, then yeah gotta be careful but generally you did the hard work in morning then kinda slacked off during midday
I grew up in North Dakota though so dunno my knowledge is more like dances with wolves. Our hottest day growing up was 114f/45ish c, I didn’t do jack that day except sit in front of a fan in the house with ac on full blast drinking ice water.
I do miss my horse from back then though, she was the best cow sense horse for wrangling cow herds. Miss ya Smokey.