A lady at my barn has a gorgeous brown almost black quarter horse mare with black mane and tail. She uses it every day on her whole body plus mane and tail and I have never seen a burnt hair on her! You could also put a fly sheet on your horse because they repel uva UVB rays and covers the whole body and the top of the tail and you can get a neck cover to cover the mane and a fly mask for the face and forelock! No way sun is getting through that!!!! If you show then it's worth it. Oh and there are great shampoos from Rio Vista to blacken the tail!!!!
I did not find it worked that well. I still had the red look in what was a pure black tail (when he lived in a stall).
I have just learned to accept the sun bleached mane and tail look. He does not look as nice as he did with the contrast of a nice black mane and tail (he too is a buckskin), but he is happier being outside.
SPF sunscreens etc don't have much effect, the cause of the bleaching effect of the hair is actually related to it drying out from the heat produced from the sun rather than the light (i.e. UVA/UVB rays).
So a good conditioner is your best bet to help keep the moisture from being sucked out of the hair shaft which leaves it dry, brittle and a rusty orange.
My girl has the same thing, although she is many differen shades of brown anyway so I quite like it. If I had a buckskin or a bay I would probably think differently!
Oh I never knew that, interesting!! Well I spray showsheen in her tail a LOT to keep it from getting tangled and every time I wash her I put conditioner in her tail as well, but maybe I should try a more heavy duty leave in conditioner as well, or one of those "hydrating" sprays like Marigold?? :)