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The impact of dark exposure on the feeding behaviour, production, and gastrointestinal tract segment and content weights of broiler chickens



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Broiler feeding behaviour was observed at two ages to quantify how varying durations of darkness alter behaviour and impact productivity and alterations in the gastrointestinal tract (GIT) over 24 h. The impact of dark exposure on productivity, GIT segment and content weights and feeding behaviour of Ross 308 broilers (7-31d) was studied. Four lighting programs were used (23L:1D (1D), 20L:4D (4D), 17L:7D (7D), and 14L:10D (10D). The birds (n=4000) were housed in 8 rooms with 8 pens per room (2 replications per lighting treatment and 4 replications per gender per room). The GIT data were collected on d 27-28 (6 males per lighting program, euthanized at 2 h intervals for 24 h). Production data were analyzed using SAS Proc Mixed as a 4 (dark) x 2 (gender) factorial arrangement and GIT segment data as a 4 (dark) x 12 (time) factorial arrangement, with lighting program nested within room. Dark data were analyzed using regression analyses and analysis of variance. Differences were significant when P≤0.05. At 31 d, regression analyses showed no effect on body weight, however numerically birds raised on 4D and 7D were heaviest. The highest feed consumption was observed under 4D. Birds on 10D were the most feed efficient (linear response). A quadratic effect on mortality was found, with the highest mortalities under 4D and 7D. Birds on 10D had the heaviest empty crops (% of body weight (BW). Crop content (% BW) changed quadratically, with peaks prior to dark under 4D, 7D, and 10D, suggesting anticipation of darkness. The empty gizzard weight (% BW) increased linearly as dark increased. Behaviour was examined as a 4 (dark) x 2 (age (2, 4 wk) x 2 (gender) factorial arrangement with lighting program nested within room. Five males and females per room were marked and focally observed. Statistical analyses were performed similar to the production data. As dark increased, feeding bout frequency increased and feeding bout interval decreased linearly. Total time spent at the feeder decreased linearly as dark increased. As birds aged, feeding frequency decreased and feed bout length and interval increased. Males visited the feeder more frequently and had shorter bout intervals. Birds anticipated dark periods >4 h and increased their feeding activity prior to dark. Broilers adapt their feeding behaviour in response to dark exposure, which alters GIT segment and content weights, and likely feed passage rates, in turn affecting feed efficiency and digestibility.



darkness, gastrointestinal tract weight, gastrointestinal content, feeding behaviour, broilers



Master of Science (M.Sc.)


Animal and Poultry Science


Animal Science


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