I think I read somewhere the significance of dried sweat being whiteish. Once last summer, and yesterday, my gelding got into a heavy sweat, just standing in the corral. It was very hot and humid the first time, but this time it was only in the 90's. The first time, I saw him in the sweat and misted him with the hose. This time, he was already dry when I saw him but the sweat had dried whiteish. I believe he is getting adequate salt. What might cause this?