Strain differences among chickens in tonic immobility: evidence for an emotionality component

Area of Science:

• Animal Behavior
• Ethology
• Comparative Psychology

Background:

• Tonic immobility (TI) is a natural defense mechanism observed in various animal species, including chickens.
• Previous research has indicated variations in TI responses among different chicken breeds.

Purpose of the Study:

• To investigate the genetic basis of tonic immobility differences in chickens.
• To explore the relationship between tonic immobility and other measures of emotionality, such as open-field activity, defecation, and adrenal weight.

Main Methods:

• Comparative analysis of tonic immobility durations across different chicken strains.
• Crossbreeding experiments to assess hybrid offspring reactions.
• Behavioral observations in an open-field test, including activity and defecation.
• Measurement of adrenal gland weight as a physiological indicator of stress.

Main Results:

• Significant strain-specific differences in tonic immobility were identified in chickens.
• Hybrid chickens exhibited intermediate tonic immobility durations compared to their parent strains.
• Strain differences in emotionality measures (open-field activity, defecation, adrenal weight) correlated with tonic immobility variations.
• Latency to defecate in the open field was strongly correlated with latency to ambulate.

Conclusions:

• Strain-specific differences in emotionality are the primary basis for observed variations in tonic immobility in chickens.
• Defecation in an open-field test may represent an intermediate response during fear reduction rather than a direct measure of fear or emotionality.