My horse had mud fever for ages and it would not abate, vet suggested Prednisolone and it cleared up really well. You have to use a lot of tablets to begin with and then taper the dose down but it does the trick. It suppresses the immune system so allows the healing process so you must be very careful to watch for any other wounds etc and just keep the affected leg clean and dry but much easier than continually picking scabs !!
If mud fever recurrs in future then check with vet again before you repeat the treatment and make sure there aren't any other problems first. Best of luck!
