Shedding of porcine reproductive and respiratory syndrome virus in mammarygland secretions of sows

Objective-To document shedding of porcine reproductive and respiratory synd rome (PRRS) virus in mammary gland secretions of experimentally inoculated sows, to evaluate effects of vaccination during gestation on virus shedding during the subsequent lactation, and to evaluate shedding of PRRS virus in milk of sows in commercial herds. Animals-6 sows seronegative for PRRS virus were used for experiment 1, and 2 sows were retained for experiment 2. For experiment 3, 202 sows in commer cial herds were used. Procedure-in experiment 1, 2 sows were inoculated with PRRS virus, 2 sows w ere vaccinated with modified-live PRRS virus vaccine, and 2 sows served as control pigs. Mammary gland secretions were assayed for PRRS virus. In expe riment 2, pregnant vaccinated sows from experiment 1 were vaccinated with a nother modified-live PRRS virus vaccine. Mammary gland secretions were assa yed in the same manner as for experiment 1. For experiment 3, milk collecte d from 202 sows in commercial herds was assayed for PRRS virus. Results-In experiment 1, PRRS virus was detected in mammary gland secretion s of both vaccinated and I of 2 virus-inoculated sows. In experiment 2, vir us was not detected in samples from either vaccinated sow. In experiment 3, all samples yielded negative results. Conclusions and Clinical Relevance-Naive sows inoculated late in gestation shed PRRS virus in mammary secretions. Previous vaccination appeared to pre vent shedding during the subsequent lactation. Results for samples obtained from sows in commercial herds suggested that virus shedding in mammary gla nd secretions of such sows is uncommon.