I have two suggestions:
1. Desitin Creamy (in drugstores and/or Amazon)
2. My Pony Sunblock (a powdered form of zinc oxide) found at: http://ecx.images-amazon.com/images/I/51u8cFYiKNL._AA160_.jpg It is free of “manufactured” chemicals: Contains ONLY Zinc Oxide and Titanium in it’s powdered form which is safe for ALL animals!
Both work extremely well. The My Pony Sunblock needs to be applied every other day or every day for best results. The Desitin is longer lasting.
Both have solved my problem with sunburn on my horse.