Effect of vaccination with a modified live porcine reproductive and respiratory syndrome virus vaccine on growth performance in fattening pigs under field conditions.

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused significant economic losses to the global swine industry. The present study aimed to evaluate the efficacy of a commercial PRRSV modified live virus (MLV) vaccine in conventionally reared growing/finishing pigs. Four barns were designated for groups A, B, C and D in the growing-to-finishing site. All pigs of the A barn were vaccinated with a commercial PRRSV MLV vaccine, whereas pigs of the B, C or D barn as control groups were unvaccinated. Twenty pigs randomly selected and tagged from each barn were serially bled at 0, 20, 40 and 60 day-post-vaccination, and tested for serological response with a commercial enzyme-linked immunosorbent assay kit. Body weights were measured to calculate the average-daily-weight gain (ADG). Serological assays indicated that the seropositivity of the PRRSV-vaccinated group was higher than that of the unvaccinated groups at 40 day-post-vaccination. ADG of group A was significantly higher than that of groups B and C, and the mean weights of groups A, B, C and D were 0.82 ± 0.017, 0.76 ± 0.016, 0.74 ± 0.019 and 0.81 ± 0.018 kg, respectively. In conclusion, the present study reports the serological responses and growth performance parameters by the PRRSV MLV vaccine in growing/finishing pigs under field conditions.