In all IBV infection groups, the viral load in both the oral and cloacal swabs generally showed a gradual decline from 7 dpi to 26 dpi. Compared with the rH120 group, The reduction in viral load between 14 or 18 dpi was significantly greater for chickens infected with rH120-S1/YZ than for chickens infected with rH120, and the viral RNA of the QX-like strain rIBYZ was lower than that of the rH120 group at 7, 14, and 18 dpi but with no statistically significance (Fig. 6 A). In contrast, the viral load in the cloacal swab of the rIBYZ group was significantly higher than that of the rH120 and rH120-S1/YZ groups at 7 dpi. Compared with other groups, the viral RNA in the cloacal swab of the rH120-S1/YZ group was significantly lower at 7, 14, and 22 dpi (Fig. 6B). No virus was detected in the control group at any time point. Fig. 6 Viral loads at 7, 14, 18, 22, and 26 dpi in the oral and cloacal swabs of chickens infected with the recombinant rH120, rIBYZ, and rH120-S1/YZ strains. All data are presented as the mean ± standard error of the mean (SEM); ***Indicates an extremely significant difference at P ≤ 0.001; **Indicates a highly significant difference at 0.001 < P ≤ 0.01; *Indicates significant difference at 0.01 < P ≤ 0.05.