Originally Posted by Mercury
There are a couple options I can think of:
1) night turnout and inside during the day
2) fly mask, fly sheet, fly leg wraps
I think that's pretty much your best bet, right there.
Walk your pasture and make sure there arent too many weeds. Milkweed will cause photosensitivity..my dark bay tobiano loves milkweed, and I discovered this one summer and he blistered and peeled wherever white was on his body, until we figured out what he was eating. Now he only gets a pink nose in the summer,but that's normal. But since your horse is probably one of the unlucky ones that just burns, I'd recommend keeping him in during the peak daylight hours and sheet him up and keep him up until the worst of the sun is over.
His rolling in dirt probably actually helps with his sunburn, mud is a good sunblock, (and fly block) but it's not what you want to see on your horse, I know. Watch the fly sprays you use on him, the oil based ones, though more effective with flies, will be like puttting tanning oil on him, making sunburn worse, and some horses with pale skin are more sensitive to the repellents anyways....
So, daytime shade and nighttime turnout, with fly sheets when sun can't be avoided.