Behavioral and physiological features of chickens diversely selected for resistance to avian disease. 1. Selected inbred lines differ in behavioral and physical responses to social stress

To test the hypothesis that genetic variations in response to social stress modulate susceptibility to disease in poultry, aggressive behaviors induced by social stress were measured in chickens of different inbred lines selected for disease resistance (line 6(3)) or susceptibility (lines 7(2) and 15I(5)), as well as 2 recombinant congenic strains (B and X). At 15 wk of age, roosters from each genetic line or strain were randomly assigned to pairs for intraline male-male aggression tests (n = 8 per line). Based on the results of the intraline aggression tests, the roosters were divided into 2 groups, winners and losers. At 16 wk of age, the roosters were randomly paired as winners vs. winners and losers vs. losers for interline aggression tests, i.e., line 6(3) vs. 7(2) and 15I(5); line 7(3) vs. line 15I(5); and strain X vs. strain B. Similarly, at 17 wk of age, line 6(3) vs. strains X and B, and line 72 vs. strains X and B were tested. The tests were conducted in a novel cage that was similar to their home cages, to provide a neutral space for both roosters being tested. Each pair was videotaped for 15 min. Male-male interaction-induced aggressive behaviors were markedly different among the genetic lines. Compared with roosters of lines 15I(5) and 7(2), line 6(3) roosters generally showed fewer aggressive behaviors, including aggressive pecks and fights, as well as durations (P < 0.05). Roosters of the recombinant congenic strains X and B, each possessing a unique random 87.5% genome of line 6(3), exhibited low aggressive behaviors, which were similar or equal to the level of line 6(3) in both intraline and interline aggression tests (P = 0.05). These results may indicate that some of the gene(s) commonly carried between strains X and B as well as line 6(3) likely played an important role in governing their lower levels of aggression. The present chicken lines may be used as animal models for investigation of the cellular mechanisms of genetic-environmental interactions on disease resistance and stress responses.