This past summer in June I discovered a lump near my horses wither. My first thought--Ouch that looks like a nasty horsefly bite lump. It was much different than any I have ever seen in 30 plus years of horses. It was maybe just a tad larger than a pencil eraser and stuck up about 3/4 or an inch. It was hard. It was in the skin, not attached to anything deeper. The hair was still on it. There was no scab, there was no indication that I could see of a bite mark--nothing like a tick would leave or a bee sting would leave behind. there was no other swelling outside the eraser sized protrusion.
Knowing what I know now, I wish I had taken a picture then, in order to give readers something to go by if you happen to be here because your horse has a strange little lump you are researching.
Anyway as it wasn't sensitive to the touch and didn't interfere with the saddle I rode the day I found it and serval times over the coming weeks. Then I noticed one day the lump became hairless and as I was rubbing My horse reacted in a way that I recognized as "OH YEAH Scratch right there!!" So I did and the hairless lump came right off in my fingers. It had that sort of "brains" look to it. It was starting to get dark so I brought it into the house to examine it.
I ripped it apart with my finger nails to see what was inside. It was fibrous but there was nothing that I could see inside. It was slightly moist. These are the pieces.
I went back outside to examine the hole in my horse. I found the divot filling with blood.
I washed it and applied Blue Kote. The next day It had dried and was scabbed over. I pressed on it to determine if it was healing clean. a tiny drop of blood seeped out from under the scab. Not healing clean. I soaked it to remove the scab and gave it a good scrubbing with betadine and peroxide. added another bit of Blue Kote. Next day it was healing clean and the day after that same. within a week it was completely closed and smooth. Now when I try to find a scar I cannot. Mystery not solved though. Vet said perhaps some minute particle in the skin caused an irritation that created this little nub of scar tissue that was subsequently ejected.