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. 2021 Apr 21;8:620347. doi: 10.3389/fvets.2021.620347

Table 4.

Risk factors described in observational studies (n = 27).

Risk factorsa (n = 84) Risk factor details
Biosecurity (n = 19) All-in-all-out vs. continuous flow (n = 7), mixing/cross fostering (n = 5), internal and external biosecurity (n = 5), air space separation (n = 2), piglet movement between stages (n = 3), infection control (n = 4), dead pig removal (n = 1)
Vaccination of dams
(n = 14)
Porcine reproductive and respiratory syndrome virus (PRRSV) (n = 4), Porcine Circovirus type 2 (PCV2) (n = 3), Enterotoxigenic Escherichia coli (ETEC) (n = 3), rotavirus (n = 1), not clear or unspecified (n = 3)
Housing (n = 13) Pen floor type (n = 4), space allowance/pig density (n = 4), use of bedding (n = 2), drinker type (n = 2), climatic and temperature conditions (n = 3), age of buildings (n = 1), indoors vs. outdoors (n = 1)
Vaccination of pigletsb (n = 11) PRRSV (n = 4), PCV2 (n = 4), not clear, or unspecified (n = 5)
Weaning (n = 9) Weaning age (n = 8), mixing at weaning or weaning management (n = 3)
Feed regime (n = 5) Restricted feeding (n = 4), creep feeding (n = 3), starter diet protein content restriction (n = 1)
Producer education
(n =4)
Experience level of manager/producer/worker (n = 3), Education level of manager/producer/worker (n = 2)
Feed type (n = 3) Pelleted nursery feed (n = 1), feed composition quality (n = 1), level of soybean and canola (n = 1)
Feed additive (n = 3) Zinc product (e.g., ZnO) (n = 3)
Air quality (n = 3) Ventilation (n = 3)

Categories of risk factors presented in order of decreasing frequency.

a

Risk factors included modifiable exposures regardless of the positive or negative impact of the exposure on an outcome.

b

Piglet vaccination includes suckling piglet or nursery pig vaccination.