Comparison of productivity losses between swine breeding herds adopting killed or attenuated PRRS virus vaccination protocols following PRRS outbreaks
Porcine reproductive and respiratory syndrome virus (PRRSv) has been endemic for more than 30 years in most pig producing countries across the globe, and is still one of the most economically important pathogens affecting swine. The use of modified live vaccines (MLV) on breeding herds has been reported by several investigators and is a common practice in the industry for the control of PRRSv. There is limited published information on efficacy of killed virus (KV) vaccines as part of PRRS control programs in breeding herds. Thus, the objective of this study was to describe productivity losses in breeding herds following PRRS outbreak that used KV vaccination protocol compared to those using MLV vaccination protocol. A retrospective observational study was conducted to describe the production impact between two exposure groups i.e. KV vaccine-boostered group (27 herd-outbreaks from 19 herds) and MLV vaccine-treated group (51 herd-outbreaks from 50 herds). A survey was used to record key demographic information including herd size (number of breeding sows in the inventory), location of gilt acclimation site (offsite or onsite), PRRS status prior to described outbreak (stable or unstable), frequency of weaning events per week (1 and 2 or 3+), PRRSv RFLP type, United States geographic region, and PRRS vaccination protocol of breeding sows (KV vaccine, or MLV vaccine). The productivity losses were calculated using ‘time to baseline production’ (TTBP), and ‘total loss per thousand sows’ (TL/1000 sows). Statistical analyses were performed with SAS version 9.4. There was no difference in TTBP between exposure groups (P 0.4242), but the herd-outbreaks in the KV vaccine-boostered group had a lower median total loss of 697 per 1000 sows compared to the MLV vaccine -treated group (P 0.0021). This study provided information about changes in productivity of commercial breeding herds following PRRS outbreak, using KV vaccination protocol as part of PRRS management strategy when compared to those using MLV vaccination protocol.