Weird disorder, any one seen anything like this?

My neighbor's horse Star, has developed a condition that is currently stumping three vets. One week ago he started with diarrhea, then began developing skin lesions that oozed sticky yellow serum until it hung off Star's coat in icicles all along the horse's topline and chest. Vet #1 put Star on a round of anti-biotics and gave him a medicated bath. Seven days later, the horse's condition has changed very little, the serum dripping has reduced some, but he has also developed severe swelling in his chest that seems to be draining down into the fore legs above the knees. When the weepy areas are disturbed(washing, rubbing) the hair peels off in chunks, the skin beneath is flaky and dry.

Vet#2 is a good friend of mine, we talked at length over the phone and I sent him blurry photo's shown below. He had few ideas.
Vet#3 was sent the photos as well but wouldn't comment until he sees the horse in person, set appointment for Saturday.



This photo is of a patch is missing hair, and is still weeping serum.




This is Star's topline, he has been wearing a blanket, so the serum has soaked into the blanket rather than hanging in icicles like it did before he was blanketed, but the extent of the lesions can be seen.



This is a patch that has lost the hair and is no longer weeping serum.


The photos of the swelling didn't turn out very well so I didn't post them. It is winter, very cold lately, so bugs really are out of the question. The horse is 18+yo. Any Ideas would be appreciated!

My first guess would be rainrot.
My second guess would be HERDA
Sorry can't see all the pics

I have no idea what that is, but I wouldn't want a blanket on him.

Which is kind of sucky, because it's so cold

The horse is 18+yo, HERDA usually requires them put down before they turn 4, so I disagree with this.

I also think it's likely to be rain rot, very bad rain rot at that! Although it might be something else such as an allergy [allergies present in some pretty odd ways!], I think chances are it's simpler than that.

Maybe if the blanket was washed with a soap, it could not be agreeing with him.

Whats the horse eating? What is the environment like? Any new changes?

I had a horse that oozed yellow serum from bug bites, mainly ticks.

Does the horse still have the diarrhea? Or is it primarily the skin problems & swelling now??

Has anyone considered pigeon fever?

I don't know much about it... but they can develop sores anywhere on their body :/ The oozing and swollen chest made me think strangles... probably not, but definitely something to be considered - especially since it is contagious.

Here is a link from the AQHA: http://quarterhorsenews.com/index.ph...in-horses.html

Actually Vet#2 said that this reminded him a lot of HERDA, the only thing that didn't fit was the horse's age.

We also discussed rain rot, but Star has been on strong antibiotics (both topical and ingested) for a full 7 days now, with little improvement, in fact the swelling in his chest started AFTER the antibiotic treatment. Our environment also is not conducive to rain rot, we live in the desert and are experiencing a drought.

The diarrhea is still persisting. The horse was not blanketed until the skin condition started, vet#1 recommended the blanket.
Star lives in a small paddock with a really nice run in shed that is sheltered on all four sides, he gets turn out into 2 acres of dry lot every other day. He eats grass hay with Equine Senior, there was a change a new hay supplier recently, I'll have to ask to see if it corresponds to the timing of his coming down with this.

If this is an allergy, it is the wildest reaction I have ever seen in a horse!