Objective—To document shedding of porcine reproductive
and respiratory syndrome (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 commercial
herds were used.
Procedure—In experiment 1, 2 sows were inoculated
with PRRS virus, 2 sows were vaccinated with modified-
live PRRS virus vaccine, and 2 sows served as
control pigs. Mammary gland secretions were
assayed for PRRS virus. In experiment 2, pregnant
vaccinated sows from experiment 1 were vaccinated
with another modified-live PRRS virus vaccine.
Mammary gland secretions were assayed in the
same manner as for experiment 1. For experiment 3,
milk collected from 202 sows in commercial herds
was assayed for PRRS virus.
Results—In experiment 1, PRRS virus was detected in
mammary gland secretions of both vaccinated and 1 of
2 virus-inoculated sows. In experiment 2, virus was not
detected in samples from either vaccinated sow. In
experiment 3, all samples yielded negative results.
Conclusions and Clinical Relevance—Naïve sows
inoculated late in gestation shed PRRS virus in mammary
secretions. Previous vaccination appeared to
prevent shedding during the subsequent lactation.
Results for samples obtained from sows in commercial
herds suggested that virus shedding in mammary
gland secretions of such sows is uncommon. (Am J
Vet Res 2001;62:1876–1880)