Risk factors associated with endemic reproductive deficiencies caused by PRRSV infection

Objective: To describe chronic reproductive losses and determine associated risk factors in swine herds positive for porcine reproductive and respiratory syndrome virus (PRRSV) in the midwestern United States. Methods: Twenty-seven PRRSV-positive breeding herds were monitored for 6 months before and 1 year after the PRRSV outbreak. Herds were statistically analyzed and assigned to one of two herd PRRSV statuses: either "recovered" if measured reproductive parameters returned to pre-outbreak levels, or "chronic" if ≥ 2 reproductive parameters did not return to at least 90% of pre-outbreak levels. Data regarding herd attributes and management practices prevailing in the herds were collected via a producer survey. Multifactorial logistic regression analysis was applied to determine associations between management practices or herd attributes and the PRRSV status of the herd. Results: Seven of 27 herds (26%) were categorized as chronic PRRSV-positive breeding herds, while the other 20 were categorized as "recovered." Two logistic models were produced for the chronic herds: one containing management factors statistically associated with a chronic PRRSV status (raising own replacement gilts, isolation of new breeding stock, number of sows per farrowing room, and inventory of growing pigs), and one identifying herd attributes (parity and sow inventory) that were associated with a chronic PRRSV status. Implications: PRRSV-positive herds can have chronic reproductive losses in which some reproductive parameters will not return to 90% of prediagnosis levels. Certain herd attribute/management factors are associated with increased or decreased risk.