To clarify sleeping behavior of neonatal chicks, two experiments were conducted. In Experiment 1, the contribution of feeding on sleeping behavior was investigated over a 24 h period. Newly hatched layer-type chicks were kept under continuous lighting, and were maintained at 28°C for one day without any food or water. Thereafter, one group was provided food and water, and another group was given only water for 23 h. The chicks were then video recorded over the next 24 h in order to quantify the following behaviors : (1) active wakefulness or sitting with eyes open, and (2) sitting or standing motionless with their eyes closed and head dropping on the ground (sleeping posture). Thereafter, the chicks were sacrificed and brain serotonin levels determined. The time fasted chicks spent in a sleeping posture was longer than in fed chicks. The serotonin content tended to be higher in fasted than in fed chicks. No significant difference in the concentration of ketone bodies was detected between fed, fast and control chicks. In Experiment 2, the differences of sleeping activity between ad libitum fed layers and broilers were examined. Broiler chicks spent more time in a sleeping posture than layer chicks, but brain serotonin content was higher in layer chicks. In conclusion, sleep in the neonatal stage was largely influence by feeding conditions, and was modified by genetic selection.
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