BEHAVIORAL-RESPONSES OF BROILER-CHICKENS TO HANDLING - EFFECTS OF DIETARY TRYPTOPHAN AND 2 LIGHTING REGIMENS

In three 2 x 2 factorial experiments, effects of added dietary Trp (0 or .2%, Experiments 1 and 2; 0 or .4%, Experiment 3) and two lighting regimens [1) constant 23-h photoperiod (23H); or 2) increasing photope riod (INC)] on behavioral responses of broilers to handling were asses sed. In Week 6 of Experiment 1, and Weeks 3 and 6 of Experiments 2 and 3, 32 chickens from each treatment were picked up and held by both le gs for 30 s, carried for 60 s, and induced into tonic immobility (TI). In all experiments, chickens reared under INC were more likely to fla p when carried, and flapped longer, than chickens reared under 23H (P < .01). In Experiments 2 and 3, INC chickens were more likely to curl the body ventrally when handled and were more susceptible to TI induct ion than 23H chickens (P < .05). The duration of TI was shorter on INC than 23H in Experiment 2 (P < .05), and longer in Experiment 3 (P < . 001). Dietary Trp supplementation resulted in a lower flapping duratio n and higher incidence of body curling in Experiment 2 (P < .05), and a shorter TI duration in Experiment 3 (P < .05). Flapping, body curlin g, and TI responses of chickens varied between handlers (P < .05). Voc alization and flapping rates were lower, and flapping incidence and du ration of flapping and TI higher, in Week 6 than in Week 3 (P < .05). Chickens reared under INC may be at greater risk of injury during pres laughter handling than chickens reared under 23H. Addition of .4% Trp to the diet may have a mild fear-reducing effect.