Agreed HorsePoor but I wonder if its bacterial in origin. We were just giving her the antibiotics to cover her because when it burst out after 4 days there was a really big hole. I posted a few photos of it. The weird thing was that her temperature remained 104F in spite of twice daily injections of NSAID's until the leg started to ooze serum and then it went back to normal. Hoopla there was no mud rash or abrasions of any sort. This is the third horse of ours that this has happened to since last August.