Mysterious bumps

[Morland]

My 5 yr old part bred NF has slight skin bumps - just enough to raise the hair, not enough to feel. He is not at all itchy. The bumps come and nearly go, mostly on his sides and quarters. They don't seem to be heat/cold related (he had them before his thick coat was clipped, and has them still 3 weeks later). He had them out at grass 24/7 and when kept in 'at school' for 2 weeks. He is not on any hard food. He is well in himself and none of the other horses has bumps. He just looks a bit odd! Like he has nettle rash, but there aren't any nettles or other such plants, or flies, about.
I think we've ruled out most of the obvious causes - does anyone have any ideas, please?

 

[orin]

have you sprayed him with anything recently? washed his rugs with anything?

sounds like he has had a reaction to something

 

[Morland]

No, and no! But thanks for your reply - I seem to have stumped everyone. It does seem like a reaction to something, but it's been going on for about 6 weeks, in which time he's no longer being fly-sprayed, fed anything but grass/haylage/hay, I haven't bathed him, he's been clipped, he's lived in for 2 weeks, and there's no change. He's never been allergic to anything before (I know his previous keeper). I'm just glad he's not itchy with it. A real puzzle. I have emailed the vet for further advice - she was mystified when she saw him.