Figure 1

Mean clinical score, cumulative mortality and mean body weight difference. A Infected birds belonging to groups L1, B1, L2 and B2 were individually scored based on the following clinical signs: 0—active with no clinical signs; 1—slightly weak with dropped wings; 2—depressed with swollen crops; 3—weak, apathetic, with ruffled feathers and reluctant to move; 4—apathetic, unable to move or stand, breathing intensely with eyes closed. An average of each group’s clinical score was calculated at each time point. All clinical signs were observed between 4 and 9 dpi. No clinical signs were observed in the control birds. B Mortality rates (%), recorded in groups L1, B1, L2, B2, L0 and B0 throughout the animal experiment. Mortality curves with different lowercase letters are significantly different (P < 0.05). C Mean differences in body weight (%) of infected birds belonging to groups L1, B1, L2 and B2 in comparison to the respective control group (L0 or B0), at 1, 4, 7, 10, 14 and 21 dpi. Values of groups B1 and B2 at 7 dpi correspond to pooled birds that were euthanized and sampled between 5 and 7 dpi due to poor condition. Asterisks indicate statistical significant difference (P < 0.05). From 7 dpi onwards there were no SPF broilers alive in groups B1 and B2.