| Summary: | Two trials were conducted with the objective of investigating the effect of light intensity, approximately within the practical levels at confinement barns (1, 10, 20 and 40 lx), on production, processing characteristics and welfare of broilers raised to 35 d of age. In each trial, 950 Ross x Ross 308 chicks were placed randomly in each room with replication of individual light intensity treatment in two environmentally controlled experimental rooms. Within each large room, a small pen with 25 male and 25 female chicks was used for recording behaviour. Data were analyzed as a randomized complete block design, considering trial as a block. All chicks were exposed to 40 lx light intensity and 23 h light for the first 7 d, followed by treatment light intensity and 17 h day length thereafter. Body weight and feed consumption were determined at 7, 14, and 35 d of age. At the conclusion of each trial, 60 birds per treatment were processed to determine the detailed meat yield. For each replicate, behaviour was recorded for the 24 h period, starting at 16 or 17 d of age. At 23 d of age, serum samples were collected from three birds per room at the start, middle and end of light and dark periods, respectively, for melatonin estimation. Skeletal and foot pad, and ocular health were monitored at 31 and 32 d of age, respectively. Broiler live production (BW, FC, FCR and mortality) was unaffected by light intensity. Carcass, thigh and drum yield as a percentage of live weight decreased linearly with increasing light intensity. The 1 lx treatment resulted in heavier wings as a percentage of live weight. Birds exposed to 1 lx rested more and had reduced expression of foraging, preening, dust-bathing, stretching and wing-flapping behaviours in comparison to other light intensities, over the 24 h period and 17 h light phase. Light intensity did not affect circadian behavioural rhythms (24 h period) and behavioural patterns over the 17 h light phase. Diurnal rhythms of serum melatonin were also unaffected by light intensity with all treatments demonstrating a pronounced rhythm. Skeletal health was unaffected by light intensity but ulcerative foot pad lesions decreased linearly with increasing light intensity. Birds exposed to the 1 lx intensity had heavier and larger eyes. In conclusion, light intensity did not affect broiler production, behavioural and physiological rhythms and mortality but did affect carcass characteristics. Increased ulcerative foot pad lesions, ocular dimensions and altered behavioural expression at 1 lx light intensity are indicators of reduced broiler welfare.
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