Determination of bacterial loads. Bacterial loads in the blood of ducks infected with R. anatipestifer Yb2, Yb2∆gldM, or cYb2∆gldM were determined at 12, 24, and 36 hpi. Bacterial colony-forming units were counted and analyzed. The data are presented as the means ± standard deviations of ten infected ducks and were analyzed using two-tailed independent Student’s t test. Asterisks indicate statistically significant differences between groups (**p < 0.01; ***p < 0.001; ns, p > 0.05).