I haven't noticed it, but I guess I would see if you're giving a lot how it could considering the color of it is kind of reddish/brown itself. I'll have to pay more attention when I start one on it.
I've fed Equisure, regularly, for quite a few years and it's never turned any of my horses' pee reddish brown. I'd be concerned you have something a little more serious going on.
We give it regularly and to a lot of horses of all ages and never had it turn the urine any color. Have you recently given your
Horse a vitamin shot? Sounds like your horse has tied up and you maybe didn't notice it, I have seen horses pee blood after tying up. You need to have some blood work done on your horse especially if it is tying up bad enough to pee blood.