Measures of fear and the response to stress in laying hens
The tonic immobility test and the time taken to approach a novel object have been used as measures of fearfulness in poultry. If there was a relationship between fearfulness and a hen's response to stress, it might be possible to identify hens whose welfare is most at risk in particular production systems.
At 30-33 weeks of age, 150 individually caged Isa Brown hens were subjected to tonic immobility tests on a least 3 separate occasions.
Two groups of hens were selected. Hens in group 1 had mean tonic immobility times of less than 70 sec and group 2 hens, mean tonic immobility times of greater than 300 sec.
At 0500h on day 1 of the study, hens were moved to transport crates and remained there for 4 h before being moved to new cages in a different part of the layer shed.
The day before moving and on days 2, 3, 5 and 7 after moving, all eggs laid were collected and weighed. The egg albumen was then removed, weighed and stored at -200C.
Between 15:30 and 16:30h on the day the hens were moved a 1 ml blood sample was taken and the plasma collected and stored at -200C.
The corticosterone concentrations in plasma and albumen were determined by radioimmunoassay.
One month later, hens from both groups were subjected to a novel object test. For this test a multi-coloured rod was placed in the feed trough and the time taken for the hens to approach the rod was recorded.
The increase in egg albumen corticosterone concentration after moving was small (group 1, 1.16 to 1.33 and group 2, 1.22 to 1.38 ng/g). This suggests that hens were not unduly stressed.
For individual hens, there was no relationship between the measures of fearfulness and the corticosterone response. Also, no relationship between the tonic immobility test and the novel object test was observed. For this strain of hen, the measures of fear were not a good indicator of how individuals responded to the stressor.
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Article made possible through the contribution of the Australian Poultry Science Symposium (APSS) 2006.