|Cheng, Heng Wei|
Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2007
Publication Date: 3/1/2008
Citation: Dennis, R.L., Cheng, Z.Q., Cheng, H. 2008. Genetic variations in chicken aggressive behavior: The role of serotonergic system. Poultry Science. 87:612-620. Interpretive Summary: Aggression and cannibalism are of increasing concern to animal welfare and production in husbandry industry. Our research group recently investigated the roles of two major serotonin receptor pathways (5-HT1A and 1B) in mediating aggressiveness in laying hens from strains exhibiting high and low aggressiveness. Our findings provide evidence for the heritable aggression mediation through genetic differences in the serotonergic system in chickens. Our results also show two distinct mediating pathways of aggression through the 5-HT1A and 1B receptors that are prominent in birds of low and high aggressiveness, respectively. The understanding of the genetic and environmental regulation of aggression through the serotonergic system is essential for reducing aggression and cannibalism through selective breeding or dietary regulations. These findings will be adopted or used by other scientists and the breeder industry in developing new strains of farm animals to improve animal well-being and maintaining economic efficiency.
Technical Abstract: Serotonin (5-HT) regulates aggressive behavior via binding to its receptors, such as 5-HT 1A and 1B, in humans and rodents. This study was designed to test if 5-HT regulating aggressiveness has a heritable component in chickens. Chickens from two divergently selected lines HGPS and LGPS (low and high aggressiveness, respectively) and DXL (Dekalb XL, an aggressive out-group) were used in the study. Hens were paired within the same strain. At 24 wk of age, the subordinate of each pair received i.p. injection of NAN-190 (0.5 mg/kg, a 5-HT 1A antagonist), GR-127935 (0.5 mg/kg, a 5-HT 1B antagonist) or saline (control) for 5 days. The frequency of aggressive behaviors were increased in the hens of DXL and LGPS treated with 5-HT 1A antagonist (p<0.05) and in the HGPS hens treated with 5-HT 1B antagonist, respectively. 5-HT 1B antagonist (p<.05) treated HGPS hens and 5-HT 1A antagonist treated LGPS hens also displayed an increased feather pecking (FP, P<0.05); but neither antagonist had an effect on FP of DXL hens (P>0.05). This may suggest the possibility of multiple mediating factors altering FP behaviors. Among the controls, LGPS hens have higher epinephrine (EP, P<0.05) levels than HGPS or DXL hens, indicative of the inferior stress coping ability of LGPS hens (P<0.05). Treatment with 5HT-1B antagonist significantly reduced EP levels in LGPS hens, but not in DXL or HGPS hens, suggesting a role of 5-HT 1B in stress regulation in LGPS hens. Hens of all strains treated with 5-HT 1B antagonist but not 5-HT 1A antagonist exhibited reduced weight gain and increased plasma 5-HT concentrations compared to controls (P<0.05), suggesting a negative feedback system altering stress coping ability. The results provide evidence for different heritable serotonergic mediation of stress coping, aggression, and FP behaviors in chickens with high and low aggressive propensities. The data also indicates that, similar to humans and rodents, 5-HT 1A and 1B have different functions in the regulation of aggressive behaviors in chickens.