qRT-PCR data were analysed for reference genes expression stability using two different statistical algorithms: geNorm version 3.5 [1] and NormFinder version 0.953 [16] according to the developers' recommendations. Raw quantification cycle (C t ) values were converted to relative quantities using the comparative C t method as input data for the two applets. Preliminary analyses performed separately on qRT-PCR data from disease-stressed animal sampled at different time points and under different environmental temperatures (August and September) retrieved consistent results. Therefore C t values were averaged after inter-run calibration according to Hellemans et al. [33] and submitted to subsequent data analysis. The combined analysis was performed processing samples from ten randomly chosen control sheep together with the disease-stressed sheep and then joining expression results in a combined dataset.