Corticosterone responses, fear behaviour and sociality in laying hens : a thesis presented in partial fulfilment of the requirements of the degree of Master of Science in Physiology at Massey University
The overall aim of this thesis was to compare behavioural measures of fear and sociality and corticosterone responses to a stressor in white Leghorn and brown Hyline hens and to examine the relationship between corticosterone and these behaviours. The first set of experiments involved taking behavioural measures of fear and sociality. Tonic immobility and open field tests were conducted to measure fear whist a runway test was used to measure sociality. There was a distinct difference in underlying fear levels with white hens being more fearful than brown, principal components analysis further distinguished this difference. There was no difference in the levels of sociality between the two strains of hen. The second set of experiments investigated the hen's corticosterone response to a 15 min handling stressor and 15 min and 60 min restraint stressors. Corticosterone responses to these stressors were measured by the collection of blood samples at 0. 15, 30 and 60 min after the stressor had begun. Both strains of hen responded to the handling procedure with a greater corticosterone response than to either restraint procedure, with no difference between the strains of hen. There was no difference in corticosterone response to both the restraint procedures but the white hens had a greater corticosterone response than brown hens. The third part of this thesis investigated the repeatability of the tonic immobility test and examined the relationship between corticosterone and fear and sociality. No difference was found in the mean behavioural measures of the first and second tonic immobility test for either strain of hen, but correlations and statistical repeatability calculations indicated that the tonic immobility test was more repeatable for brown than white hens. Correlations were found between corticosterone and behavioural measures of fear and sociality in white hens only. Principal components analysis supported these findings and indicated that there was a positive relationship between corticosteroid and fear and a negative relationship between corticosterone and sociality. The findings of the present study have provided information about the behavioural and physiological responses of white Leghorn and brown Hyline hens and show that the use of derived measures such as principal components analysis can provide useful information about relationships between variables in laying hens.