The reproductive performance of sows after PRRS vaccination depends on stage of gestation

In order to minimize the effects of porcine reproductive and respiratory sy ndrome (PRRS) on stillbirth, mummification, and neonatal mortality in swine herds, many producers have vaccinated their herds using a modified-live vi rus vaccine, The purpose of this study was to determine the association of the PRRS modified-live vaccine and reproductive performance by stage of ges tation when the vaccine was administered. A total of 47 swine herds from On tario and Manitoba, Canada, and from the mid-western USA were included in t he study. Participating farms had vaccinated all of their sows at one point in time when they used the vaccine for the first time. The reproductive pe rformance of sows that farrowed in the year prior to use of the vaccine was compared to that of sows vaccinated in each of five stages of gestation an d in the gestation that followed the initial use of the vaccine. Sows vacci nated at any time during gestation had a reduced number of pigs born alive, a reduced number of pigs weaned per litter, and increased number of stillb orn pigs and an increased number of mummified pigs compared to the sows tha t farrowed prior to use of the vaccine. The largest association was seen in sows that were vaccinated in the last four weeks of gestation, The largest losses were observed in those herds that were vaccinated concurrently with the initial PRRS herd outbreak. These results suggest that the modified-li ve vaccine should only be administered to non-gestating sows. (C) 1999 Else vier Science B.V. All rights reserved.