Alternative housing styles may affect stress levels of hens. In the Coalition for Sustainable Egg Supply (CSES) study researchers reviewed the impact of housing systems on bird stress through assessment of laying hen blood chemistry.

The wing vein blood of two flocks at weeks 18 and 77 was used to determine the heterophil-lymphocyte ratios (H/L) and total white blood cell counts (TWBC). H/L values from aviary housed and conventional caged birds were not statistically significant, while the H/L ratio of enriched colony birds was two times higher. However, the high variability among cages suggests the H/L ratio is not an effective indicator of stress when applied alone.

The TWBC analysis indicated an increase in the number of white blood cells, and a high frequency of irregularly structured cells, which signify a higher stress response. However, it was noted that the presence of bacteria, fungi and yeasts in the blood could have accounted for these elevated levels as well.