You are right Happy Hippy that show herds are open to more risk of picking up and spreading disease as a pigs worst enemy is another pig but having shown pigs for many years I have never had a health issue from being at a show.
Most show pigs go to shows from an isolation unit and come back to one. They spend 3 weeks in the unit before they go to their first show and 3 weeks in it after the last.
In properly ventilated trailers pigs should arrive without any stress and I have never seen an over heated pig unloaded at a show. The greatest worry is that you find yourself in a motorway snarl up for hours on a hot day but that could happen on any journey. I always carry water.
New pigs to any holding should ideally be isolated for three weeks. Three weeks being the time most severe illnesses will show up and hence the three week standstill pig keepers have observed prior to the other standstills brought in after foot and mouth.
As with all animals housing, especially with poor ventilation, increases the risk of disease spreading rapidly. As does over stocking, inside and out. Over a period of time over stocking and grazing will potentially cause problems.
Hughsey you are correct the BPA recognises only the Britsih Saddleback now however some lines do tend more towards Essex or Wessex traits in their conformation and finished carcase.