Fear-related responses of white Leghorn hens of several genetic stocks in five-bird cages and associations with quantitative traits.

Hens of 8 genetic stocks derived from a common foundation population were compared at three ages for latency to recover from tonic immobility (TI) and from an avoidance response following exposure to a metronome. Body weight, feather score, and egg-production traits also were measured. A total of 350 hens was involved and individuals of the same genetic stock were kept together in 5-hen cages from 19 to 70 weeks old. The TI and metronome avoidance tests were conducted in three rounds at mean ages of 35, 48, and 61 weeks. Hens of stocks with increased egg mass, resulting from selection, did not differ from unselected controls for TI or avoidance responses. Straincross hens also did not differ from parental strain means for these fear-related behaviors. Time to recover from induced TI decreased with repeated testing at 13-week intervals. Hens exposed to the metronome a second time within the first round recovered more rapidly than did those tested in this way for the first time. Previous indirect exposure to the metronome also resulted in reduction in avoidance time. Correlation analysis revealed only a moderate association between TI and avoidance responses (r = .23, P less than .01). Avoidance responses were not associated with any other quantitative trait in the 5-hen cage environment. Duration of TI was moderately associated with body weight (r = .22, P less than .01) and had a complex relationship with total egg mass produced, which was associated with the interval in cages prior to testing. There was no apparent correlation of TI and egg mass when TI was measured on 35-week-old hens, heterogeneity of correlations was present among genetic stocks tested at 48 weeks, and a negative association was detected when TI tests were conducted at 61 weeks (r = -.46, P less than .01).