What the textbooks don’t tell you about…Backtracking by rats and flies

Backtracking is the colloquial term for the transmission of disease from older pigs to younger ones. The older pigs usually have had time to build a satisfactory immune shield, while the younger animals have yet to do so, and can succumb to disease, carried in clinical or subclinical form by their older companions in the unit. In order to reduce this risk it is good that segregation by age is becoming more common on pig units and the textbooks encourage this development.   However in my op