Heritabilities of Tonic Immobility and Leucocytic Response in Sire and Dam Layer Lines


Abstract: Fearfulness reaction was examined using tonic immobility (TI) response and differential leucocyte counts as physiological indicators of distress from sire and dam brown layer lines. The study was performed on 20 male and 131 female chickens from the sire line and 24 male and 116 female chickens from the dam line. The duration of TI, the time interval until the bird righted itself, and the number of inductions (15 s periods of restraint) necessary to attain TI were recorded. If TI could not be induced after 5 attempts, a score of 0 was recorded. After the TI test, blood samples were collected from 16 male and 45 female chickens in the sire line and 17 sires and 42 dams in the dam line and leucocyte parameters were examined. After the normality test, TI, tonic immobility per number of inductions (TI/Ind) and the heterophil:lymphocyte (H/L ratio) showed deviations from normality. After applying the Box-Cox transformation all data were analysed by a general linear model using JMP. Heritabilities and phenotypic correlations were also obtained Significant line differences were obtained from TI reactions. There were no significant differences in the leucocytic parameters between lines, except for eosinophils. The H/L ratio was significantly higher in males than in females. Heritability estimates for the duration of TI and TI/Ind were low to moderate in the sire line, but moderate to high in the dam line. The results suggest that fearfulness could be controlled through selection.

Keywords: Tonic immobility, leucocytic traits, heritability, layer line

Full Text: PDF