Effects of specific noise and music stimuli on stress and fear levels of laying hens of several breeds

The purpose of the present study was to analyze the effects of specific sound stimuli on heterophil to lymphocyte ratio and tonic immobility duration of laying hens. There were two different experiments. The first experiment (216 birds) measured heterophil to lymphocyte ratio and tonic immobility duration in 36-week-old hens of four Spanish breeds of chickens (Castellana, Villafranquina, Vasca, and Prat) exposed to specific noise stimuli of 65 dB (background chicken vocalizations and fans, control) or 90 dB (background noises plus truck, train, and aircraft noises) for 60 min, between 8.00 and 9.00 once. There was significant difference for the heterophil to lymphocyte ratio between noise treatments (P < 0.01), the ratio of hens treated with noise being higher than that of control hens. Treated hens had significant heterophilia (P < 0.01). There was significant difference for the duration of tonic immobility between treatments (P < 0.001), tonic immobility duration being significantly longer in the group of hens treated with noise. Thus, hens exposed to 90 dB noise were more stressed and fearful than control hens, as indicated by the heterophil to lymphocyte ratio and the tonic immobility duration, respectively. Results were consistent across the breeds. The second experiment (108 birds) measured heterophil to lymphocyte ratio and tonic immobility duration in 36-week-old hens of two different Spanish breeds of chickens (Leonesa and Andaluza) exposed to background noises (65 dB) or to specific classical music stimulus plus background noises (75 dB) between 9.00 and 14.00 for three days. There was no significant effect of music treatment on the heterophil to lymphocyte ratio, its numerator or its denominator, whereas there was significant effect for the tonic immobility duration (P < 0.001), tonic immobility of hens treated with music being longer than that of control hens. Thus, hens exposed to specific music stimulus were more fearful than control hens. The results of the present study indicate that specific noise stimulus (90 dB versus 65 dB) causes stress and fear in laying hens and specific classical music stimulus (75 dB versus 65 dB) has a negative influence on their fearfulness. © 2004 Elsevier B.V. All rights reserved.