Vaccination against Streptococcus suis: Effect on nursery mortality

Purpose:To evaluate the effect of selected vaccines and administration routes on mortality of nursery pigs due to Streptococcus suis. Methods: A field trial was conducted on one group of nursery pigs (N=330). Pigs were randomly allocated to one of four groups that each received one of the following treatments at weaning: an experimental autogenous vaccine administered intramuscularly (IM) (n = 90); a standard autogenous vaccine administered IM (n = 90); a commercial bacterin, administered intraperitoneally (IP) (n = 60); or no vaccine (n = 90). Nursery mortality was monitored from the start of the trial (18 days of age) until the end of the nursery period (9 weeks of age). Results: Nursery mortality before the start of the trial was approximately 17%.There were no significant differences among the four treatment groups; however, there was a trend toward decreased mortality among pigs that received the experimental autogenous vaccine. Overall nursery mortality at the end of the trial had decreased to 3.3%. Following the trial, an IP vaccination protocol with the commercial bacterin was initiated among all nursery pigs for 6 months.Total nursery mortality while this protocol was in place was 3.48% (SD = 1.45) and the mortality rate for pigs that showed CNS signs at the time of death was 2.55% (SD = 1.2). After this 6-month vaccination program, the owner of the herd switched to a sow vaccination strategy with the commercial bacterin. For the 6 months during which the sow vaccination protocol was monitored, total nursery mortality was 2.66% (SD = 1.65), with mortality of pigs demonstrating terminal CNS signs at 2.0% (SD = 1.61). Implications:Vaccination does not totally control S.suis.