The aim of the study was to estimate the efficacy of Streptovac vaccine in controlling Streptococcus suis infections in field conditions in swine, Streptovac vaccine contains no less than 8.5 × 108 inactivated cells of S. suis type 2 and a similar number of S. suis type 1/2. The vaccine includes two adjuvants: aluminum hydroxide and mineral oil (Emulsigen). The experiment was performed on 3 farms: S, H and P with total of 4,400 sows (3,000, 1,100 and 300 sows). Clinical symptoms of streptococcosis occurred mainly among weaners between 7-8 weeks of age. Clinical signs associated with changes in the central nervous system were mainly observed. Losses due to streptococcosis in farms varied from 4-6%. Streptovac was used to immunize pigs from 3 different experimental groups in each farm. In farm S - 1,462 farm P - 447 and farm H - 1,307 animals were vaccinated. Vaccination was performed just before weaning and 3 weeks later; 2 ml of vaccine was applied i.m. One group of pigs in each farm served as the control. The parameters of production in every experimental group were compared with the results in the control group in order to evaluate the efficacy of the vaccine. The following criteria were evaluated: percentage of weaners with clinical signs of infection, percentage of pigs which died from streptococci with body weight on the day of weaning and moving from weaning house to fattening house, mean body weight gains during the 2 month period of observation. The analyzed results indicated a significant reduction in all farms in the average number of pigs with typical signs of infection in the central nervous system: in farm S - 4.58% in the experimental group and 7.92% in the control one; in farm P - 6.04% and 9.33% and in farm H - 3.74% and 6.56%. A similarly significantly lower mortality rate in was observed in the vaccinated pigs. The average death rate for control groups in farm S - was 4.87% and for experimental groups 1.64%; in farm P - 6.00% and 3.13% and in farm H - 4.17% and 2.06%. The differences between body weight gains among vaccinated and control pigs were not significant. To summarize, Streptovac vaccine used in farms where streptococcosis is caused by field strains cross-reacting with vaccine strains ensures a significant reduction of losses caused by S. suis.
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