I'm interested too as my horse has developed a number of soft swellings over his body including a fairly big one on his belly. I thought they might be a reaction to fly bites of some sort?
It is very strange as he has never reacted to flies before. A big swelling came up on his side on wednesday / Thursday then on Friday he had colic, which he has never had before, no idea if could be related. Now he has several swellings all over his body.
Actually just thought, my other horse once came up in swellings after having a lot of rich haylage from a differnt source than normal. Have you changed hay / haylage recently?
wipe the areas with tea tree that is soothing. and if they are fly bites it will repell them as well if the horse comes down with any more than the ones he has got dont go away in about 3 days i would call the vet for some advice!
My chestnut had a big lump on his stomach and a swollen sheath a week or so ago. It went down in a few days though so thinking that was fly bites too. I would give them a day or two and see if they change.