Iowa State University – “Investigation of factors impacting the rate of PRRSV transmission in nursery and finisher pig flows and assessment of transmission rate and timing on economic performance”

Summary:
The purpose of this project is to identify herd management or facility factors that can be manipulated to affect the rate of PRRSV transmission and to provide producers with specific information that can be incorporated in herd plans to most profitably influence the rate of PRRSV transmission. This project will identify farm facility, management and pig flow characteristics that influence the rate of PRRSV transmission and growth performance in nursery and finisher pigs. This will be achieved by following 30 groups (cohorts) through nursery and finisher flows that represent a cross-section of facility design and management systems. Cohorts will be identified and blood sampled at two-week intervals during the entire nursery and finisher phase. Serological results from these samples will be used to determine the rate of PRRSV transmission within each group. The association between 46 farms, flow and pig variables and an increased rate of transmission will be evaluated to prioritize risk factors for within-farm transmission of the virus. Additionally, the rate and pattern of infection will be analyzed in the context of closeout performance data (average daily gain, feed conversion, weight, etc.) to evaluate the impact of infection timing and rate of transmission on economic performance.

Objective:
Three objectives have been identified in this project. First, an estimate of the rate of PRRSV transmission in the nursery and finisher phases of commercial pig flows will be determined. Second, farm characteristics that affect the rate of transmission will be identified. Third, the effect of infection timing and rate of transmission on economic performance of groups will be calculated.

Relevance:
This research addresses Step A of research objective 3 of the PRRS Initiative, Within farm transmission. Once a herd is infected, PRRSV tends to circulate in an endless cycle of subclinical episodes. The common belief is that the virus is perpetuated in an infected herd by a cycle of transmission from the dam to her pigs, then by pig-to-pig contact at later stages of production. Under conditions in which susceptible and infectious pigs are mixed, e.g. at weaning, a large proportion of the contact population may quickly become infected. For that reason, it is surprising to find that field research has, in fact, found marked differences in transmission rates between groups, pens and even rooms of animals in infected herds. Thus, there is a clear need for field research focused on PRRSV circulation in pigs and the factors that impact rates of transmission within farms.