Herd factors associated with the seroprevalences of Actinobacillus pleuropneumoniae serovars 2, 3 and 9 in slaughter pigs from farrow-to-finish pig herds.

This cross-sectional epidemiologic study was conducted in 150 randomly selected farrow-to-finish pig herds to investigate descriptive epidemiological characteristics of infections with three different serovars of Actinobacillus pleuropneumoniae, and to identify risk factors for the within-herd seroprevalences of these serovars. Different farm characteristics (n = 28) were examined as potential risk factors for the percentage of pigs with antibodies against serovars 2, 3 and 9. The presence of antibodies was measured using an indirect ELISA. Logistic regression analyses were used to assess the associations between the potential risk factors and the proportion of seropositive pigs. The median within-herd seroprevalences were 95% (range: 0-100%), 100% (range: 10-100%), and 35% (range: 0-100%) for serovars 2, 3, and 9, respectively. There was a positive association (P < 0.001) between each of these serovars. The within-herd seroprevalence of serovar 2 was significantly higher in farms that purchased gilts from > or = 2 origin herds (OR = 2.33; P < 0.05) and in farms with poor biosecurity measures (OR = 4.62; P < 0.05). The proportion of pigs seropositive for serovar 3 was significantly higher when tested pigs were slaughtered in May-August and in November-December (OR = 5.96; P < 0.001), in herds without a growing unit (OR = 2.63; P < 0.01), and in herds with a direct air-entry into the finishing unit (OR = 1.92; P < 0.05). The within-herd seroprevalence of serovar 9 increased significantly in herds with poor biosecurity measures (OR = 1.76; P < 0.05). The study documented that infections with A. pleuropneumoniae serovars 2, 3, and 9 were very common in the selected herds, and that the sero-epidemiological characteristics and risk factors showed some variation depending on the serovar. The purchase policy of gilts and biosecurity measures are risk factors that can be improved fairly easily on pig farms.