One of my goats had this happen to him this spring- his skin swelled up on his lower legs so much it actually split open over his cannon bone. Very nasty! Vet said put him down, but I wanted to try- I soaked his legs in warm epsom salt water daily, then slathered on udder balm. Gave him penG once a day every 3rd day, for 4 shots total. Within a week I saw major improvement, and now 3 months later it is completely healed and no scarring.
Vet said it was due to excessive moisture causing a bacterial infection. This was the wettest spring ever, for a month it was just soupy mud everywhere. I have no doubt it was from the mud and muck.
Spent a whole hour today laying in a pasture, waiting for a sparkling vampire to show up. Alas, I woke up and looked over, only to find a mound of horse crap. Sigh.