Effects of an acute stressor on fear and on the social reinstatement responses of domestic chicks to cagemates and strangers

MARÍN, R. H.; FREYTES, P.; GUZMÁN, D. A.; JONES, R . B.

APPLIED ANIMAL BEHAVIOUR SCIENCE

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2001 vol. 71 p. 57 - 66

0168-1591

Abstract      Genetic selection for appropriate levels of sociality (motivation to be with conspecifics) could benefit poultry welfare and performance. Runway tests that require chicks to traverse a corridor in order to reach other chicks in a goal box are commonly used to measure sociality. However, we need to determine if the chicks´ responses are sensitive to selected experiential variables before we can recommend test criteria. The present study focused on fear and on the identity of the stimulus birds. Broiler chicks either remained undisturbed or were exposed to an acute stressor (mechanical restraint) before their tonic immobility fear responses were measured one hour later in Experiment 1. Exposure to the stressor significantly prolonged tonic immobility and, hence, presumably, underlying fear levels. In Experiment 2, the runway responses of stressed chicks and undisturbed controls were assessed when the goal box contained either familiar or unfamiliar chicks. Our finding that stressed chicks emerged from the start box sooner and spent longer near the stimulus birds suggests that exposure to a frightening event increased social reinstatement motivation. Furthermore, social affiliation was more pronounced when the goal box contained familiar cagemates rather than strange chicks, regardless of prior treatment. This finding demonstrates that broiler chicks can discriminate between familiar and unfamiliar conspecifics encountered in novel surroundings. In view of the present findings we recommend that exposure to frightening events prior to test should be avoided and that the identity of the birds in the runway goal box should be standardized, i.e. familiar or unfamiliar, and noted.      Genetic selection for appropriate levels of sociality (motivation to be with conspecifics) could benefit poultry welfare and performance. Runway tests that require chicks to traverse a corridor in order to reach other chicks in a goal box are commonly used to measure sociality. However, we need to determine if the chicks´ responses are sensitive to selected experiential variables before we can recommend test criteria. The present study focused on fear and on the identity of the stimulus birds. Broiler chicks either remained undisturbed or were exposed to an acute stressor (mechanical restraint) before their tonic immobility fear responses were measured one hour later in Experiment 1. Exposure to the stressor significantly prolonged tonic immobility and, hence, presumably, underlying fear levels. In Experiment 2, the runway responses of stressed chicks and undisturbed controls were assessed when the goal box contained either familiar or unfamiliar chicks. Our finding that stressed chicks emerged from the start box sooner and spent longer near the stimulus birds suggests that exposure to a frightening event increased social reinstatement motivation. Furthermore, social affiliation was more pronounced when the goal box contained familiar cagemates rather than strange chicks, regardless of prior treatment. This finding demonstrates that broiler chicks can discriminate between familiar and unfamiliar conspecifics encountered in novel surroundings. In view of the present findings we recommend that exposure to frightening events prior to test should be avoided and that the identity of the birds in the runway goal box should be standardized, i.e. familiar or unfamiliar, and noted.