Internal inclusions in brown eggs: relationships with fearfulness and stress

Abstract

Tonic immobility reaction and heterophil: lymphocyte ratio (indices of fearfulness and stress, respectively) were studied in hens laying eggs with or without internal inclusions (blood and meat spots). Two brown egg Spanish breed of chickens were used. There were no significant differences between groups in terms of tonic immobility duration. Birds of the group with internal inclusions appeared to be less fearful when defined by the number of inductions to achieve tonic immobility (1.4+/-0.1 vs 1.1+/-0.1; P < 0.01). Tonic immobility duration was significantly shorter in the group of hens with internal inclusions, when only those laying the abnormal egg the day before measurement of tonic immobility were included in this group (264+/-33 vs 395+/-30 s; P < 0.01). There was a significant difference in the heterophil:lymphocyte ratio between the two groups of hens (P < 0.01), mean value being significantly higher in the group with internal inclusions (0.43+/-0.02) than in the control group (0.33+/-0.02). Hens that laid eggs with internal inclusions had significant heterophilia (P < 0.01). Differences were consistent across the breeds. The incidence of internal inclusions was significantly greater (P < 0.001) in eggs with pink shells (an abnormality associated with the effect of stress). The results suggest that the laying of eggs with internal inclusions involves changes in fearfulness and stressfulness of hens.