Abstract: In order to study of step down-step up lighting program on performance and respiratory and circulatory system in broiler, a research was conducted in a completely randomized design, consisting of 2 treatment each in 4 replicates. Total 120 day-old male commercial hybrids of cobb chicks were randomly distributed over 2 rooms, at 14 day of age 1 room with a 23 h light: One hour dark lighting schedule and another room with an step down-step up lighting schedule. The length of the trail was 6 weeks. At 21, 28, 35 and 42 days of age, 1 bird from each pen was randomly selected and weighted before euthanizing. The blood samples were collected for hematocrit assay. The relative weight of the organs (heart, lung, right and left ventricle), abdominal fat percent and characteristics including body weight gain, feed intake, feed convertion ratio were measured at the end of each rearing period. At the end of experiment, 2 birds from each pen were euthanizing for carcass quality. The results of statistical analysis of data obtained indicated that there was no significant effect of lighting program on relative weight of lung and heart, carcass fragment percent and weight gain but there was significant effect on hematocrit percent at 4 and 5 weeks of age, relative weight of right ventricle to both of right and left ventricle (p< 0.01). Abdominal fat percent of lighting program chicks was lower than of continues lighting broiler (p< 0.05). In all rearing period lighting program had significant effect on feed intake and feed convertion ratio (p< 0.01) except in 21 day old. The advantages of slowing down early growth of an Step down -Step up Lighting Schedule are of economic significance in terms of improved feed conversion efficiency and reduced losses due to metabolic disorders such as ascites in broiler chickens.
S. Golzar Adabi , G. Moghaddam , A. Taghizadeh , S. Noomi , J. Davoodi , A. Nematolahi and H. Karimi , 2007. The Effect of Step down-Step up Lighting Schedule on Broiler Performance . Journal of Animal and Veterinary Advances, 6: 1055-1059.