Tonic Immobility Reaction and Heterophil to Lymphocyte Ratio in Hens from Three Spanish Breeds Laying Pink Eggshells

Tonic immobility reaction and heterophil:lymphocyte ratio were studied in hens laying pink eggs from three brown egg Spanish breeds (Barred Red Vasca, Red Vasca, Red Villafranquina). There was no significant difference among breeds in terms of tonic immobility duration or heterophil:lymphocyte ratio. Tonic immobility duration was significantly shorter in the pink (220 + or - 23 s) than in the normal brown shell group of hens (416 + or - 23 s; P < 0.001). Differences were consistent across the breeds, tonic immobility of hens laying pink eggs being shorter than that of control hens in all three breeds. Birds of the group with pink shells appeared to be less fearful when defined by either the duration of tonic immobility or the number of inductions to achieve it. There was a significant difference in the heterophil:lymphocyte ratio between the two groups of hens (P < 0.001), mean value being significantly higher in the pink shell (0.73 + or - 0.03) than in the control group (0.35 + or - 0.03). The heterophil:lymphocyte ratio from the pink shell hens increased significantly in the three breeds. Hens that laid pink eggs had significant heterophilia and lymphopenia (P < 0.001). Thus, hens laying pink eggs were less fearful and more stressed than control hens, as indicated by the tonic immobility reaction and the heterophil:lymphocyte ratio, respectively. A significant negative correlation was found between both measurements (r = A).28; P < 0.01). A similar significant negative association (P < 0.001) was found between pink shell color and shell strength.