The objective of the present study was to evaluate the temperament of a native Japanese chicken breed (TosaJidori) using the tonic immobility test for the detection of fearfulness. Each chick (2, 5, 10 or 15-day old) was placed on its back on a table and restrained by hand. Thereafter, if the chick lay still, it was then released and observed. The number of inductions and tonic immobility duration was recorded. The duration in the male was shorter than that in the female at 2-day old, whereas higher than that in the female at 15-day old. The duration of tonic immobility was affected by age in the male (P＜0.05). There was a positive correlation between them in the male, and a negative correlation in the female. As for the number of induction, no significant differences and tendencies were found between sex and age. These findings demonstrate that Tosa-Jidori chicks show sexual differences in the fear response and further suggest that the temperamental differences may correspond to genetic characteristics of breeds.

Activation of the right hemispheric neurotransmitter systems is related to negative emotion and stress in mammals, but this relationship is not fully known in birds. The effect of the presence of sawdust litter on behavior and brain monoamine laterality in isolation stressed chicks (6 days old) was investigated. Although there was no significant difference in peep, movement distance in litter group chicks (n＝7) was significantly longer than that in non-litter group chicks (n＝6) during 15 min isolation test (P＜0.01). The laterality index (a measure of central monoamine laterality indicating the predominance of right over left hemispheric activity) of serotonin (5-HT) in intact chicks (no stress manipulation; n＝8) was higher than those in chicks with and without litter substrate (P＜0.01). The value of the dopamine (DA) metabolite ratio in intact chicks was lower than that in the non-litter group chicks (P＜ 0.05), but was not low in the litter group chicks. In contrast, there was no significant difference in the levels of the 5-HT metabolite ratio among the groups. In addition, the laterality index of the ratio correlated negatively with the number of peeps in chicks with sawdust litter (P＜0.01). It has been suggested that emotional processing in the right hemisphere might be optimal with DAergic and/or serotonergic lateralization, whereas either a decrease or an increase in this lateralization might be reinstated in animals suffering stress. In addition, the present results imply that sawdust litter may attenuate isolation stress that induces anxiety in chicks, and that the laterality index of the DA metabolite ratio may be effective in estimating positive emotional change.

No abstract