We have had trouble in the past with pigs with rash/hives, we have never found the root cause of this. It always took place later in the year meaning late July. This year it has started earlier and we want to get it taken care of.
It starts in the arm pit area and spreads throughout and currently has covered the body.
Other pigs have a small amount. We have a new barn, clean shavings and an overall healthy environment for the pigs. If you have any information on how to treat PLEASE share. Thank you so much!

It sounds like mites or biting flies. I would spray the pigs down with bronco and spray the pens down with permethrin. I would do this every couple of days. Also give the pigs a round of ivermectin.