Copper deficiency?

[TexasBred]

I changed minerals to a southern states 2:1 graze and gain mix and within about two days the red was gone. They are all black as night. The first set of minerals were crap or they just didn't like them.

Some of it was probably just dead hair in the process of shedding. The difference between good mineral and poor mineral is sometimes no more than a couple bucks a bag but the fortifications and sources of the fortifications can be dramatic.