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Abstract
1. This trial studied the effects of strain and age on tonic immobility (TI) duration, emergence time (ET) and social reinstatement time (SRT) in laying hens and investigated the consistency of individual behavioural characteristics over rearing and laying periods and the correlations between these behavioural traits.
2. One hundred chicks from each of ISA Brown (ISA) and Lohmann Tradition (LT) laying hens were reared from one day old in pens. At 3 weeks, birds of each line were divided into 4 groups. Twenty birds in one group of each line were marked individually for repeated testing and the other groups were assigned for single testing to test the habituation effect and possible age effects at a group level.
3. ISA birds had higher overall means for TI duration and latency to leave the start box. ISA also showed longer latency in SRT at week 28 than Lohmanns. TI duration increased from weeks 3 to 10 and then decreased to week 35 in both lines. The latency to explore the test area and to reinstate decreased from weeks 10 to 35.
4. Tonic immobility, exploratory and social reinstatement behaviours were consistent over time in both lines, as revealed by Kendall's W coefficient of concordance.
5. In social test situations, an inter-situational consistency was found, that is, birds emerged quickly from the start box and reinstated quickly with their companion. TI (non-social test) was negatively correlated with ET and SRT. Thus the two lines of laying hens respond differently in social and non-social tests.