RESUMO
In order to evaluate the usefulness of the enzyme-linked immunosorbent assay (ELISA) in determining the optimal age for infectious bursal disease virus (IBDV) vaccination in broilers under field circumstances, the percentage of birds susceptible to vaccine at vaccination age was estimated in 12 flocks on the basis of ELISA titres in newborn chicks. The effective percentage of susceptible birds at the day of vaccination was checked by comparing virus neutralization (VN) titres measured in sera taken immediately before vaccine administration with the breakthrough titre of the vaccine used. In nine of the 12 flocks, the ELISA had largely overestimated the percentage of susceptible birds. Subsequently, to examine the performance of the ELISA kit, 815 chicken sera were comparatively examined in ELISA and VN tests. Results demonstrated a linear relationship between mean ELISA titres and VN titres. It was concluded that the ELISA could be a useful tool in IBDV vaccination timing, but that interpretation criteria should be adjusted to avoid vaccination at too early an age.
