sunscreen for horse

[charle@tpc.tulane.edu (Charlene Bartholomae)]

Hi,
        I have a horse who was allowed some years ago to develop a very
bad case of rainrot.  As a result, he has several areas on the very top of
his back (where the saddle sits) that have little or no hair to protect him.
He is a sorrel and the skin in these areas is dark.  
        Can any of you out there, esp. vets, help me to determine what, if
anything, I can use as a sunscreen on this guy?  I tried zinc oxide, but it
really makes a mess, and actually seemed to make things worse.  I was
thinking about Flysect Super C or one of those fly sprays w/sunscreen???
        Any help will be appreciated.
        
 ,
/,`\
` | \____\\
 _(      ) \    Charlene Bartholomae
 \-\~~~_|\  \     Department of Pathology
 `  \ `   \  `       Tulane Regional Primate Research Center
                               18703  Three Rivers Road.
    `     `            Covington, Louisiana  70433
                          e-mail: charle@tpc.tulane.edu    (504)892-2040 Ext 243
                          home phone (504)748-4377     ccrydr@i-55.com