Day-old chicks categorised on latency to peck, exhibit a stable fear pattern until 15 days of age

Day-old chicks of both sexes were individually categorised on the latency to peck pebbles and termed as high latency (HL), moderate latency (ML) or low latency (LL). Anxiolytic doses of diazepam diminished the latency only in the HL category, suggesting that it is the most anxious category. At 15 days of age, the LL category showed the lowest latency to ambulate in the open-field the lowest immobility duration in the tonic immobility test and insensitivity to anxiolytic doses of diazepam in both behavioural tests suggesting that it is the less anxious category. The increase of the central benzodiazepine receptor density induced by acute stressors was the highest in the most anxious and/or fearful HL category. There were more females than males in the LL category and inversely in the HL category there were more males. The results suggest that the fear pattern depends on the sex and inter-individual differences within a same sex which are stable across life. This could be used as a test for fear and/or anxiety state, and useful to choose fowls with the best performance later in life. (C) 2001 Elsevier Science B.V. All rights reserved.