Effects of cold stress and Salmonella Heidelberg infection on bacterial load and immunity of chickens

We analysed the effects of cold stress (19 ± 1°C, 6 h /day, from the first to the seventh day of life) applied to specific pathogen free (SPF) chickens. On experimental Day 1 (ED1), chicks were divided into four groups: C (not infected and kept under thermoneutral condition); CS (not infected and cold stressed); PC (Salmonella Heidelberg (SH) infected and kept under thermoneutral condition) and PCS (SH infected and cold stressed). High concentrations of corticosterone were found in the cold stressed birds on ED7 and ED21, with a greater increase in birds of the PCS group. Stress or non-stressed SH-infected birds had high levels of norepinephrine on ED21. On ED21, an increased percentage and number of SH were found in birds of the PCS group. On ED7, a decrease in macrophages presenting MHCII, CD8+ and CD8+ γδ cells was observed in the chickens of the CS group. Decrease was observed in CD3+ cells in the birds of the PCS group and increase in macrophages presenting MHCII cells and of the CD4+/CD8+ ratio in c...