Management factors associated with seropositivity to Lawsonia intracellularis in US swine herds

Objective: To determine risk factors for Lawsonia intracellularis seropositivity in the breeding and grower-finisher units of US farrow-to-finish swine herds. Methods: Serum was collected from 15 breeding females and 15 grower-finisher pigs per herd in 184 farrow-to-finish herds, a subset of 405 herds in the National Animal Health Monitoring System (NAHMS) Swine '95 Study that examined management, health, and productivity in herds with at least 300 finisher pigs. Sera were tested by indirect fluorescent antibody test for L intracellularis. Test results were linked with NAHMS questionnaire data, and a logistic regression model of management factors associated with L intracellularis serological status was developed. Separate models were used for breeding and grower-finisher units. Results: Risk factors for seropositive breeding units were L intracellularis-seropositive status of the grower-finisher unit, use of a continuous system of management for the farrowing unit, and a young parity structure (< 75% multiparous sows). Risk factors for seropositive grower-finisher units were L intracellularis-seropositive status of the breeding unit, the number of pigs entering the grower-finisher stage, raising pigs on concrete slats, and intensive management compared with raising pigs on outdoor lots. Implications: Use of all in-all out management in the farrowing house and an older parity structure in the sow herd were associated with a lower risk of L intracellularis seropositivity in the breeding unit, and slatted concrete flooring in grower-finisher houses was associated with a greater risk. Alteration of these management factors might improve control of L intracellularis infection in farrow-to-finish herds.