Vet#1 finally called back today and said the cultures grew RINGWORM!?!? Ringworm sounds ridiculous to me, it doesn't explain the bizarre swelling, the weeping serum or the diarrhea.
Vet#3 is coming tomorrow for a second opinion and to take blood samples, I will request Dex, a good dose of steroid certainly couldn't hurt this horse now. We started a round of penicillin last night since he finished the course of uniprim prescribed by Vet#1, but nothing has changed.
Star, has been off of the new hay for 4 days, everything else in his world is the same as it has been for over a year. Vet#1 gave him a medicated bath 6 days ago, which didn't improve anything, so a contact allergy seems unlikely. Food allergy is still possible, maybe.
It might be possible that worms are the culprit, but I would be extremely surprised if parasites were involved in any way. This horse has been on a very strict worming schedule for over a year now. My neighbor bought Star last October, he came from a home where he was used as a ranch horse and received minimal care, but for the last year, while he has been with my neighbor, he has had the absolutely the best of care.