Effects of porcine reproductive and respiratory syndrome vaccination in breeding-age animals

Little is known about the safety and efficacy of extra-label use of the modified live porcine reproductive-and-respiratory syndrome (PRRS) virus vaccine in gestating sows. Our purpose was to determine the impact of vaccination on reproductive performance in 54 herds in Ontario, Manitoba (Canada) and the mid-western United States that were PRRS-positive, PRRS-negative, or concurrently affected by an outbreak of PRRS when initially vaccinated. Majority-vaccinated herds vaccinated ≥50% but <100% of sows at one time, and limit-vaccinated herds vaccinated <50% of sows at one time. Most majority-vaccinated herds did not vaccinate sows in late gestation, and none vaccinated during the initial PRRS outbreak. Numbers of pigs born alive and weaned decreased when pregnant sows were vaccinated. The effect of vaccination on productivity in the gestation following vaccination depended on the vaccination protocol.     

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

In order to minimize the effects of porcine reproductive and respiratory syndrome (PRRS) on stillbirth, mummification, and neonatal mortality in swine herds, many producers have vaccinated their herds using a modified-live virus vaccine. The purpose of this study was to determine the association of the PRRS modified-live vaccine and reproductive performance by stage of gestation when the vaccine was administered. A total of 47 swine herds from Ontario and Manitoba, Canada, and from the mid-western USA were included in the 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 performance 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 and in the gestation that followed the initial use of the vaccine. Sows vaccinated 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 stillborn pigs and an increased number of mummified pigs compared to the sows that 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-live vaccine should only be administered to non-gestating sows.