Analysis of heterophil to lymphocyte ratios in laying hens kept in a small group housing system

The objective of the present investigation was to assess the level of stress imposed on two different layer lines kept in a small group housing system Eurovent German with two group sizes and three tiers. A total of 615 Lohmann Selected Leghorn (LSL) and 633 Lohmann Brown (LB) hens were examined in four consecutive trials. Based on differential white blood cell counts, the heterophil to lymphocyte ratio (H/L-ratio) was calculated as an indicator of stress. The H/L-ratios significantly differed among the two layer lines, with 2.5-fold higher H/L-ratios in LB than in LSL. No significant differences across and within layer lines could be found between the different group sizes. A significant 0.7-fold decrease of the H/L-ratio could be shown in LSL layers when the space per hen was increased from 828 to 920 cm2.