Any fly mask/sheet is going to filter the sun somewhat, and don't forget to reomove the fly masks at night. They arent' meant for night vision. I also use a fly mask to keep excess dust out of my gelding's "bad" eye (he puntured the cornea years ago, the vet didn't want to remove the eye, so it's still in)
Yes, most any sunblock lotion (Bull Frog seems to work best-and a little goes a long way!) or zinc based diaper ointment, that's water/sweat proof as drinking water will rinse it off, and I'm sure some gets rubbed off in the course of the day from grazing, scratching, etc.
Someone mentioned the 'artificial eyeliner" but I'm not crazy about tattooing eyelids. For one, it's like getting a tatoo on your arm, it doesn't stop the sun damage, just makes it less visible to you thanks to the pigments in the tat.
My paint doesn't really burn , unless he's gotten into some milkweed (it has toxins that make horses photosensitive) then he really blisters, no matter what you do. I have to make sure he can't find any! Not a problem in good grazing pastures, but more so in over grazed or sparse pastures where weeds tend to flourish. Horses get bored and try to eat the weeds. There are some horses that get "dew poisoning" where they tend to react to the sun if turned out on wet grass in the mornings. Just depends on the horse. In these cases, I'd try to keep the horse in shade as much as possible during the most intense sun.
Oh, and should mention that certain grooming products can make your horse more sensitive. Shapely's MTG that is so popular for growing out manes/tails etc can cause sunburn in your horse. I've trimmed a few horses that reacted to it, and they burned on their shoulders/butts where the stuff melted down their bodies after being applied to the mane/tail. Usually just a problem with the paints, esp the overos.If you wash it off or keep your horse in the shade, it's not such a big deal.
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