In regards to MTG for mud fever/mud scald...I have used it and had undesirable results. My mare is a grey with pink skin - the MTG burned her skin. It made the mud fever worse by inflaming the skin around it and causing the area to become very very sore. The skin cracked open and was oozing.
This was a couple of years ago and since then I have learned that for my horse, just leaving the scab alone and not washing and picking is beneficial. When I wash the scabs and remove them, I find the infection spreads. If I leave scab alone, it eventually disappears with no ill affects to my mare.
I only intervene if the leg swells from the infection - which has only happened once.
This does not work for everyone - I know people who have left the mud scald alone and it spread severely.
I have discovered over the years that mud scald is different on every horse and not one treatment will work for all cases! Good luck!
Just thought I'd would let you know of my experience. Remember...this works for me...it may or may not work for you.