Tonic immobility and adrenal response in chickens fed supplemental tryptophan

S. Popova-Ralcheva, D. Gudev, V. Sredkova, P. Moneva

Abstract: Tonic immobility duration was tested in 24 Label chickens at 34 and 49 d of age, whereas and adrenal response to catching and subsequent 30 min long crating were studied before (36 d of age) and following dietary tryptophan supplementation for 15 d (51 d of age). Seventy nine percent of the studied chickens showed short duration of tonic immobility (less fearful) whereas the rest of the chickens had several times longer tonic immobility duration (extremely fearful). Adrenal response to catching was higher in the chickens which had longer duration of tonic immobility but the response to 30 min crating after catching was similar in all chickens irrespective of the tonic immobility duration. Dietary tryptophan supplementation for 15 d reduced (P>0.05) tonic immobility duration in the extremely fearful chickens. Supplemental tryptophan alleviated adrenal response to catching and crating (P>0.05), but plasma corticosterone did not correspond to the duration of tonic immobility in each individual. Our data suggest that tonic immobility duration as an indicator of fear does not correspond to the strength of adrenal response to catching and crating because of the complexity and transient nature of the fear emotion.

Keywords: animal welfare; chickens; corticosterone; crating; fear; handling; tonic immobility; tryptophan

Date published: 2019-10-16