Mean anti-IBV ELISA antibody titres of the control (n = 8) and vaccinated groups ( n = 5) at 0, 7 and 14 dpv. Data are expressed as mean values ± SEM. The positive cut-off titre of 396 is indicated with a dotted line. Different letters indicate significant differences (p < 0.05) within time points, determined using one-way ANOVA. D0: Day 0; DW: Drinking water; ON: Oculonasal.