Table 1 Explanatory variables investigated in the statistical models obtained from the questionnaires with unit managers during farm visits June 2003 – August 2004

Herd attributes

Indoor or outdoor unit

Nucleus or commercial unit

Finisher site

Number of sows (median 327, range 20 – 2300)

Attending veterinarian specialist pig veterinarian

Multiple site herd

Pigs ever moved between sites

Different system for sick pigs

Sick pigs ever moved back to original batch group

Purchased gilts mixed with sows

Time after purchasing that gilts are mixed with sow group (median 3.5 days, range 0 – 16)

Presence of separate gilt housing

Mixing of pigs with different batches

Purchased stock

Purchase gilts

Purchase boars

Purchase semen

Biosecurity

Presence of quarantine facilities

Quarantine facilities on- or off-site

Period of time incoming stock are isolated (median 6 days, range 0 – 28)

Isolated stock exposed to other pigs in the herd

Isolated stock tested for disease

Semen tested for disease

Protective clothing worn by employees

Pig-free time and who this applies to (median 48 hrs, range 0 – 168)

Footdip onto the unit and who this applies to

Parking of vehicles on- or off-site

Presence of a wheel dip onto the unit

Characteristics of nearest pig unit

Proximity of nearest pig unit (median 2 miles, range 0.1 – 17)

Nearest pig unit indoor or outdoor unit

Nearest pig unit nucleus or commercial unit

Nearest pig unit finisher site

Number of sows on nearest pig unit (median 250 sows, range 0 – 2000)

Rodents

Birds observed in pig housing

Rodents observed in pig housing