|Cheng, Heng Wei|
Submitted to: International Society of Applied Ethology
Publication Type: Abstract Only
Publication Acceptance Date: 5/17/2006
Publication Date: 10/8/2006
Citation: Dennis, R.L., Muir, W.M., Cheng, H. 2006. Effects of raclopride on aggression and stress in diversely selected chicken lines. International Society of Applied Ethology. p. 144. Interpretive Summary:
Technical Abstract: Lines of White Leghorn chickens were divergently selected for high (HGPS) and low (LGPS) group productivity and survivability. The selection resulted in two distinct genetic lines characterized by differential cannibalism, flightiness, and immunocompetence; resulting in differences in coping with social stress. HGPS birds have a superior stress coping strategy when compared with LGPS birds or birds of Dekalb XL (DXL), a commercial strain. The line's unique characteristics in stress response and the changes in behavior and production could be reflected in the selection-induced different expressions of dopaminergic system. The genetic basis of differential role of the dopamine 2 (D2) receptor activities in aggressiveness was examined in the diversely selected chicken lines. At 65 wk of age, birds of the same strain were housed in pairs; the dominant bird was treated with raclopride injections (or saline) for ten consecutive days to determine the differential role of stress coping ability in aggressive responsiveness to a D2 antagonist. Following treatment with raclopride, a D2 antagonist, dominant birds of all strains showed reduced frequency of aggressive pecks (P<0.05; n=15). While untreated subordinates paired with raclopride injected birds increased pecking frequency (P<0.05). Two days after treatment, LGPS and DXL birds returned to pre-injection levels of aggressive threats (P>0.05), while HGPS birds maintained a depressed frequency of threats (P<0.05). In addition, strain differences in aggressive responsiveness coincided with an increase in epinephrine in raclopride treated LGPS birds (P<0.05) but not in HGPS and DXL birds (P>0.05) relative to intra-line controls. Our findings suggest a functional linkage between the genetic basis of stress coping ability and the dopamine system regulating aggressive responsiveness. The data further indicate that the sympathetic-adreno-medullary axis is directly involved in regulating both stress coping strategy and aggressiveness.