If not most likely a haematoma (sp?) - my boy had very similar which we think was most likely from either a kick or him running into something.
Check very carefully for puncture wounds - I don't know your area, but we get quite a lot of adders round us, and know more than one horse that has been bitten right on the chest in that area. On nice warm days (like we have had today, and for the last few days) they do like to be out basking in the sun.
Looks like a haematoma to me too. My horse had one a few years ago from a kick that came up very quickly (morning no sign of it, that evening it was there). The first vet said not to worry and leave it until we got down the next day to find it was the size of a small melon! Hope he's ok x
looks like a haematoma, common place for a kick. Friends horse had one in the same place, same size from a kick. Hot and cold poultice it to get rid of it faster, but it will go in a few days or so.
its a fly bite bite,one of our liverys horses has just had one,she had the vet out and he gave her a jab and some bute for a few day's,it was in the exact same place but on her left side.he said not to keep her in as she is better off moving around.
Me for a haematoma.
My old boy had one in the same place, took ages to go, and we never found out what he'd done to get it.
He only had one boob though not two !!
My friend's colt had one in the same area, after showing too much interest in another colt. Got a kick to the chest. It went after a while. It might also be a fly bite. Either way, just keep an eye on it.