EFFECTS OF SEVERAL STRESSORS ON TONIC IMMOBILITY REACTION OF CHICKENS

Duration of tonic immobility, and number of inductions required to att ain it, were studied in adult hens from different Spanish breeds There were five experiments designed to evaluate the effects of several tre atments on fearfulness: 1) corticosterone at 60 ppm in the diet; 2) as corbic acid at 400 ppm in the diet; 3) heat stress at 42 C; 4) cold st ress at 1 C; 5) prelaying stress, hens being sampled inside a trapnest 1 h after they had been opened. Treatments 1 to 4 were begun 1 day be fore measurements of tonic immobility. Two treatment groups were used in each experiment (stressor versus control). One hundred and ninety-t wo 40-wk-old hens were equally divided into eight breeds by two treatm ent groups, each group consisting of 12 hens; in Experiment 5, the tot al number of hens was 144, divided into six breeds by two treatment gr oups. Supplemental corticosterone in diet increased significantly the duration of tonic immobility, when righting time was combined with num ber of inductions (P < .05). Addition of ascorbic acid did not change significantly the latency until righting. The duration of tonic immobi lity was significantly less (P < .05) in heat-stressed than in control hens. The effects of cold stress varied from breed to breed (signific ant interaction, P < .05), differences between treatments being signif icant in one breed; in that breed cold stress decreased duration of to nic immobility. Hens sampled inside a trapnest appeared to have signif icantly less duration of tonic immobility than control hens (P < .001) .