The impact of dark exposure on broiler feeding behavior and weight of gastrointestinal tract segments and contents.

Ross 308 broilers were observed at 2 ages to quantify how duration of darkness affects behavior and alters the gastrointestinal tract (GIT, segment and content weights) over 24 h. Four treatments provided 1 (1D), 4 (4D), 7 (7D), or 10 (10D) h of darkness. Birds (n = 4000) were housed in 8 rooms with 8 pens per room (2 replications per treatment and 4 replications per gender per room). The GIT data were collected on day 27 to 28 (6 males per treatment, euthanized at 2 h intervals for 24 h) and expressed as a percentage of body weight. Data were analyzed as a completely randomized design, with treatment nested within room. Production data were analyzed as a 4 (dark) x 2 (gender) factorial arrangement and GIT data as a 4 (dark) x 12 (time) factorial arrangement. Regression analyses established relationships between darkness and dependent variables. At 31 d, regression analyses showed no effect on body weight. The highest feed consumption was observed under 4D. Mortality was lowest under 10D. Birds on 10D were the most feed efficient and had the heaviest crops. Crop content interacted with time of day, with peaks prior to dark under 4D, 7D, and 10D. Empty gizzard weight increased linearly as dark increased (P < .01). Behavior was examined as a 4 (dark) x 2 (age) x 2 (gender) factorial arrangement of treatments. Five birds per gender per room were focally observed for 24 h. Dark data were examined using regression analyses and an analysis of variance assessed age and gender data. As dark increased, feeding bout frequency increased and total time spent at the feeder decreased linearly (P = 0.01 and P < .01, respectively). As birds aged, feeding frequency decreased and feed bout length increased. Males visited the feeder more frequently. Birds anticipated dark periods >4 h and increased feeding activity prior to dark. Broilers adapt their feeding behavior in response to dark exposure, which alters GIT segment and content weight and likely feed passage rate.