This study was conducted to investigate hen's needs for light intensity and circadian rhythm using a light tunnel with five identical compartments each at a different fluorescent light intensity of<1, 5, 15, 30 or 100 lux. The hens were able to move freely among the compartments. A group of four W-36 laying hens (23 - 30 weeks of age) was tested each time, and six groups or replicates were conducted. Behaviors of the hens were continuously recorded, yielding the data on time spent, feed intake, feeding time, and eggs laid at each light intensity and inter-compartment movement. The results show that the hens spent 6.4 h (45.4 %) at 5 lux, 3.0 h (22.2 %) at 15 lux, 3.1 h (22.1 %) at 30 lux, and 1.5 h (10.3 %) at 100 lux under light condition; and thatthey spent 10.0 h under dark (< 1 lux). Daily feed intake was 87.3 g/hen-day which was distributed as 24.8 g/hen (28.4 %) at <1 lux, 28.4 g/hen (32.5 %) at 5 lux, 13.8 g/hen (15.8 %) at 15 lux, 14.5 g/hen (16.6 %) at 30 lux, and 5.8 g/hen (6.7 %) at 100lux. Hen-day egg production rate was 96.0 %; and most of the eggs were laid at <1 lux (61.9 % of total) which was significantly different from other light intensities (P < 0.05). The hens displayed a circadian photoperiod of 10 h darkness (<1 lux) and 14 h light or 14L.10D, which is different from the typical commercial practice of 16L:8D photoperiod. The light and dark periods were distributed intermittently thoughout the day, with time spent in the darkness being 25.0 ±0.4 min per hour.
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