Urine content

[Cindy <clb@micron.net>]

I just notice that our 9 years ago geldings urine is leaving a white
coloration on the stall dirt after drying.  The horse has been on
pasture/ with grass hay with a small amount of oats and bran all
summer.  He was stalled for a day while some pasture work was
completed.  This is when I notice the urine leaving the discolor.  He is
hard to get weight on and is ridden only about once a week at the
present time. I have no problem with my mare that I ride limited
distance on the same diet.  Is this a sign of and unbalance in the
feed?  Cindy