Tonic immobility responses of white leghorn hens affected by induction techniques and genetic stock differences.
Level 5 - mechanism / opinion, no new human data
Non-human animal study
PubMed 6701136 · doi:10.3382/ps.0630001
What was done
The authors evaluated tonic immobility (TI) induction and duration in White Leghorn hens under varying handling techniques and genetic backgrounds. Tested conditions included immediate 15-second dorsal restraint versus temporary single-cage confinement prior to restraint, degree of body support during restraint, and variation in pen-catching duration. Latency to first gross leg movement, first gross head movement, and righting time were measured across strains selected for part-year egg mass, unselected controls, and strain crosses.
What was found
Immediate dorsal restraint induced TI in approximately 70% of hens, compared to 46% when hens were temporarily caged before restraint. Providing less body support during restraint increased initial induction rates. Eye closure occurred in ≤15% of hens, while vocalization or jumping at termination occurred in ~80%. Increased catching time shortened latencies to initial leg and head movements but did not affect righting time. Latency correlations were r = 0.41 to 0.71 (P < 0.01) between leg and head movements, r = 0.51 to 0.99 (P < 0.01) between leg movement and righting, and r = -0.62 (P < 0.05) to 0.96 (P < 0.01) between head movement and righting. Selected egg-mass strains displayed faster head movements than unselected controls, and strain cross performance matched parental averages for righting time, indicating additive genetic variance.
Why it matters
This study establishes that behavioral fear responses in poultry are highly sensitive to minor handling variations and physical support, while confirming that tonic immobility righting duration reflects additive genetic traits useful for breeding selection.
Limits
The abstract does not state the total sample size (n), the number of replicates, or exact variance metrics. Findings are restricted to female White Leghorns under laboratory-induced restraint protocols and cannot be generalized to other breeds or natural stress responses without further testing.
Cited by
- partial Flipping an aggressive rooster or bird onto its back induces a state of calm (tonic immobility).