MMune - start them on it two weeks before if possible (so you know for next time) and keep them on during and two weeks past.
DWorm A- Do keep them updated- consider having them on during the event to help their bodies knock out eggs they ingest then 3 days in a row after. Yes, worm ovum will be even floating in the air (manure flakes off in small particulate and goes airborn- with worm ovum attached) and is breathed in. Consider a program for yourselves as well- we have Dr Christopher herbal parasite formula under human products.
HerBiotic herb mix- this is for bacterial, viral, fungal, yeast (can we say fair) issues. One can make herb balls if you like per my blog article and give them a couple per day and for three days after to help their bodies knock out things as they are exposed. Rabbits, Guinea pigs, Poultry, hedgehogs and other small creatures benefit from HerBiotic extract. Many will lick a drop or two off of the eye dropper. Or 6 drops can be added to a day's supply of water.
Consider keeping Eucaplyptus globulus (on our site under essential oils) on hand. I put a tiny smear (not a whole drop) on my clean finger tip and smear it under nostrils twice per day. if you milk then on the milkstand is perfect. this helps knock out buggies in the lungs that they are breathing in and helps them expectorate the barn air dust.
GI Soother is incredibly helpful to have on hand in case of diarrhea. It's very easy for kids, even adults to pick up something from fair or exhibition facilities that gives them diarrhea. Sometimes just the fair and moving stress will do it.
Everyone have a Safe and BLESSED time out there with your herds!