ASSESSMENT OF THE EFFECTIVENESS OF VACCINATION AGAINST PSEUDORABIES IN FINISHING PIGS

Whereas the clinical efficacy of vaccination against pseudorabies has been studied extensively, methods to evaluate the influence of vaccina tion on pseudorabies virus (PRV) transmission have only recently becom e available. In this study, PRV transmission and growth performance in finishing pigs vaccinated either once or twice were compared. The inc idence of PRV infections was significantly (P = 0.039) higher in the g roup vaccinated once (38%) than in the group vaccinated twice (10%). T he reproduction ratio R, which is defined as the average number of new infections caused by 1 infectious individual, was estimated in both g roups. This ratio was also significantly (P = 0.025) higher among sing le vaccinated pigs (R = 3.4) than among pigs that had received double vaccination (R = 1.5). In compartments where serologic evidence of PRV introduction was observed, the mean daily weight gain was significant ly (P = 0.029) lower in pigs vaccinated once (698 g/d) than in pigs va ccinated twice (721 g/d). Results of this study document the possibili ty to objectively evaluate the effect of vaccination on PRV transmissi on under field conditions. From the results, we concluded that double vaccination is advantageous in populations of finishing pigs at risk f or PRV introduction. However, even among pigs vaccinated twice, extens ive spread of PRV can occur.