The length of time required for isolation is dependent on the incubation time of the disease and the time it takes for a measurable immune response. The animals are tested on arrival at the isolation facility, exposed to naive herd animals after 30 days and retested prior to moving into the herd at 60 days. The second best opportunity to transmit disease is via secretions from pigs such as feces, semen, and mucus. Certain diseases such as PRRS are transmitted very well in semen. To prevent PRRS from entering a herd, the semen used for AI must be certified free of virus.
Manure is a very good vehicle for disease transmission.
Most viruses and bacteria will live for extended periods of time if kept moist in manure or mucus particularly if it is kept cold. Dead stock removal is very important for a number of reasons. Keeping rendering trucks far from the swine facility as they can harbour large numbers of disease organisms - even those that are not currently in your facilitiy. If you dispose of dead stock on your own property these pigs can be a source of ongoing contamination. This is particularly true for diseases that can live in rodents, dogs and cats.