Development and implementation of a monitoring system for PRRSV status classification and study of the PRRSV stability on production parameters in Spanish breeding herds

Porcine Reproductive and Respiratory Syndrome (PRRS) is an endemic swine disease causing significant production and economic losses. Knowledge of PRRS epidemiology at breeding farms is crucial to develop control strategies against this disease. In that regard, classifying breeding herds according to PRRS virus (PRRSV) status provides great applied knowledge for developing disease control programs and to evaluate the production impact of PRRSV infection in breeding sows. The aim of this study was to establish a systematic monitoring program for PRRSV in Spanish sow farms and to evaluate the production differences between stable and unstable breeding herds. Thirty-five breeding herds belonging to a large integrated Spanish group were classified according to a standardized PRRSV infection status using sampling programs and terminology currently adopted in the United States swine industry, during a one-year study period (February 2017-March 2018). Differences in abortions (ABTHS), born-alive piglet (BAR) and pre-weaning mortality (PWMR) rates and in the number of weaned piglets/1000 sows (WPTHS) between unstable and stable farms were evaluated using a general linear mixed model on a weekly basis. According to monitoring, 15 farms achieved a stable PRRSV status after the first 4 consecutive samplings and 20 farms were classified as unstable. One of the farms maintained a stable status throughout the whole monitoring period. Among the 20 farms classified as unstable at the beginning of the monitoring protocol, 9 farms never reached the stable status and 11 farms reached stable status afterwards during the monitoring period. Regarding production differences between PRRSV farm status, significant improvement due to the achievement of PRRSV stability were observed on BAR (+1.08%), PWMR (-0.95) and WPTHS (+25.2). On a yearly basis, PRRSV stabilization would represent an increase of 1.3 piglets/sow/year. Systematic monitoring for PRRSV in breeding herds established a basis of knowledge of PRRSV epidemiology at the farm level and provided key data to classify farms according to PRRSV status. This classification allows veterinarians and producers to evaluate the production productivity benefit of the achievement of PRRSV stability in breeding herds