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

From: Porcine reproductive and respiratory syndrome virus (PRRSV) in GB pig herds: farm characteristics associated with heterogeneity in seroprevalence

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