EFFECTS OF LIGHTING PATTERN AND DIETARY TRYPTOPHAN SUPPLEMENTATION ON GROWTH AND MORTALITY IN BROILERS

The effect of lighting pattern and supplementation of the diet with Trp on growth and mortality of male broiler chickens was evaluated in three experiments using 2,392, 2,608, and 2,400 chickens, respectively. There were two lighting treatments, either a constant 23 h of continuous light/24-h period or an increasing photoperiod lighting system, i.e., 0 to 3 days, 23 h light (L): 1 h dark (D); 4 to 14 days, 6L:18D; 15 to 21 days, 10L:14D; 22 to 28 days, 14L:10D; 29 to 35 days, 18L:6D; 36 to 42 days, 23L:1D. The design was a completely randomized 2 x 2 factorial, with four replicates per treatment. In the first two experiments, a starter diet with or without .2% supplemental L-Trp (feed grade) was fed from 0 to 3 wk of age and a finisher diet with or without .2% supplemental Trp was fed from 3 to 6 wk of age. In the third experiment, the level of supplemental Trp was .4% in the starter and finisher diet. Birds raised on the increasing light pattern consumed less feed during the first 3 wk, were lighter in weight at 3 wk, and had lower feed:gain ratios (P < .001) than their counterparts on constant light. By market age (6 wk) they had similar body weight but feed intake was significantly (P < .05) lower in all experiments, and feed:gain ratio was significantly lower in these birds in Experiment 3 (P < .05) than in their counterparts on constant light. The increasing light pattern was associated with reduced total mortality and mortality from Sudden Death Syndrome (SDS) (P <.05 in Experiments 1 and 2, and P < .01 in Experiment 3). There was also reduced mortality from ascites with increasing light (P <.001) in Experiments 1 and 2, although the overall incidence of ascites was low (<1%). The incidence of varus leg abnormalities was reduced with increasing light (P < .05), and the birds appeared to be more mobile than those on constant light as judged by their ability to jump up onto a raised platform to feed. Supplementing the diet with Trp had no significant effect on growth performance, total mortality, SDS mortality, or ascites mortality. The blood heterophil:lymphocyte ratio was higher at 5 than at 2 wk (P < .001) but was not affected by lighting pattern or diet. The overall incidence of SDS was approximately 9%, suggesting that the basal diets used in this study may be of interest to other researchers studying the etiology of this condition.