I really doubt if this area will ever catch up to the rest of the world, it's still pretty backwards here. There only one equine vet hospital in a 400 mile radius, 2 vets that will do "field surgeries", and I haven't had any that ask to do fecal testing for worms, I don't worm every 2 months I do it 3 times a year, after the first hard freeze, after it quits freezing, and mid summer, we don't get the bot fly's in this area.
As far as tell the OP to use penicillin for the infection, I went through that with a mare last year, that's was I was told to do by my vet, because he couldn't get out until the next day to flush her out. Perhaps I should have qualified that in my post.
As far as getting information from books that's were the vets get it during school.
And I believe I was right on when I told the OP it was postpartum discharge.
As far as a reaction to antibiotics the vet doesn't know either if there will be a reaction, until the meds are given. Granted most people don't keep epinephrin in their med box in case of a reaction, but I do because I have a horse allergic to bees.