Effect of smooth switching the light on/off under intermittent LED lighting on the productivity of laying hens

. The influence of smooth switching the light on/off on the productivity and viability of laying hens of the SP-789 cross was studied. In the experiments, three identical groups of 120-day-old birds were formed. In the first preliminary experiment, poultry was raised up to 410 days of age, in the second main experiment it was raised up to 350 days of age. All birds were kept in cage batteries under intermittent LED lighting. The light was turned on at 2-3 am, 8-12 am, and 2-5 pm. In both experiments, lights were switched on and off instantaneously in the control group. In the first preliminary experiment, the sunrise and sunset imitations took place each time the light was switched on and off, and lasted 3 minutes in the experimental group No.1 and 6 minutes in the experimental group No. 2. In the second main experiment, in the experimental group No.1 the mode of imitation of sunrise and sunset was similar to that of the experimental group No. 1 of the first preliminary experiment. In the experimental group No. 2, sunrise was simulated only during the first light turn on, and sunset was simulated during the last light turn off (3 min). The best results were obtained in the group with smooth switching the light on at the beginning of the first photoperiod and smooth switching the light off at the end of the last photoperiod (for 3 min). As compared with control, this group showed an increased livestock livability (91.7%) by 1.9%, egg production (171.6 eggs) and yield of egg weight (9.81 kg) per initial and average laying hen by 7.3% and 6.5%. Feed efficiency per 10 eggs (1.33 kg) and 1 kg of egg weight (2.32 kg) decreased by 5.0% and 4.5% respectively.

When raising poultry in windowless poultry houses, artificial lighting is the only source of light. Artificial lightning is characterized by the lighting system, the duration and frequency of alternation of light and dark periods, the intensity of lighting and the radiation spectrum [1,[7][8][9].
Until recently, incandescent and traditional fluorescent lamps were mainly used for lighting poultry houses. The beginning of the production of lighting systems with LEDs can be considered as a revolutionary stage in the lighting of poultry houses [10]. LEDs have long service life and can be of various wavelengths [11,12]. They are characterized by low power consumption [13], the possibility of providing local lighting of poultry, low maintenance costs [14]. The high efficiency of LED lighting sources in keeping laying hens is shown in numerous studies [6,15,16].
At present, the intermittent light day (17)(18)(19)(20) is mainly used in the Russian industrial poultry farming for the cage keeping of egg hens. The long-term studies of traditional and LED lighting sources in keeping egg hens in closed windowless poultry houses have shown that repeated abrupt switching the light on/off in intermittent daylight conditions resulted in increased nervousness and stress of birds and, therefore, inhibits the achievement of high genetically determined vitality and productivity of hens.
This work aimed to study the effect of smooth switching the light on/off (simulation of sunrise and sunset) under intermittent LED lighting on the productivity and viability of egg hens of the productive flocks and to establish a rational mode of light simulation.

Materials and methods
To achieve the set aim, two experiments (the first preliminary and the second main) were carried out using the hens of the productive flocks of cross SP-789 in the vivarium of Federal Scientific Center "All-Russian Research and Technological Institute of Poultry" of RAS.
The 120-day-old hens were divided into 3 groups of 216 heads each. The hens were kept in cage batteries (6 animals in a cage) up to 410 days of age in the first preliminary experiment and up to 350 days of age in the second main experiment. Intermittent 1L:5D:4L:2D:3L:9D (L-light, D-darkness) light regime was used in the experiments. The light was turned on at 2-3 am, 8-12 am, and 2-5 pm. White warm spectrum LED lamps with color temperatures of 2700-3200 K were used; the illumination intensity at the level of the feeders was 10 lx on average.
In both experiments, lights were switched on and off instantaneously in the control group.
In the first preliminary experiment, the sunrise and sunset imitations took place each time the light was switched on and off, and lasted 3 minutes in the experimental group No.1 and 6 minutes in the experimental group No. 2.
In the second main experiment, in the experimental group No.1 the mode of imitation of sunrise and sunset was similar to that of the experimental group No. 1 of the first preliminary experiment (the best group). In the experimental group No. 2, sunrise was simulated only during the first light turn on, and sunset was simulated during the last light turn off for 3 min each.
Other keeping and feeding conditions were identical for all poultry groups and met the recommended standards.

Results
The results of the first preliminary experiment (Table 1) show that gradual switching the light on/off (imitation of sunrise and sunset) in the experimental groups Nos.1 and 2 resulted in increased livability of laying hens by 2.8% compared with the control, where lighting was instantaneously turned on and off (without imitation).
The live body weight of laying hens was not influenced by the light switching mode, no reliable differences between the groups were recorded at all age periods.
The egg production per initial and average laying hens was the highest in the experimental group No.1 (lights were smoothly switched on and off for 3 minutes). These indicators were 3.6-6.6% and 2.6-4.5% higher than in the control and the experimental group No.2, respectively. The lowest egg production was recorded in the control group.
The average egg weight in the control group was 0.5-0.6 g or 0.87-1.05% worse than that in the experimental groups Nos.1 and 2, but the difference between the groups was not statistically significant. The yield of egg weight per initial and average laying hens was the highest in the experimental group No.1. These indicators were 3.2-8.3% and 2.3-6.2% higher than in the control and the experimental group No.2, respectively. The lowest values were in the control group.
Poultry received complete fodders according to the norms recommended for the SP-789 cross, so the feed consumption per head per day in all groups was almost the same (111.0-111.1 g). However, the feed efficiency per unit production was the lowest in the experimental group No.1, 2.2-4.2 and 2.1-5.6% lower for 10 eggs and 1 kg of egg weight than in the control and the experimental group No.2, respectively. The laying hens of the control group spent the most feed per unit of production.
The second main experiment ( Table 2) showed that during the whole period of keeping chickens the highest livability was registered in the experimental group No.1 with imitation of sunrise and sunset at each switching the light on and off. This indicator was 0.9-2.8% higher than in the control and the experimental group No.2. This indicator was the lowest in the control group, with instantaneous switching the light on and off.
As in the first preliminary experiment, smooth switching the light on/off had no effect on the live body weight of hens, in all age periods the groups did not differ significantly in this indicator.
The laying hens of the experimental group No.2 reached the 5%, 25%, 50%, 75% and peak egg production 2-3, 1-2, 3, 5-6 and 35-77 days earlier, respectively, than those in the control and experimental group No.1. The control and experimental group No.1 differed little by the age of achieving the specified levels of productivity. However, the hens of the experimental group No.1 reached the egg production peak 42 days earlier than in the control group. During the experiment period, 2.3-7.3% and 2.0-5.8% more eggs were obtained per initial and average laying hens in the experimental group No.2 than in the control and experimental group No.1, respectively. The lowest values were observed in the control group, when the light was turned on and off without imitation of sunrise and sunset.
There were no significant differences in egg weight between the groups. However, the experimental group No.2 showed a higher egg production, so 3.4-6.5% and 3.2-5.1% higher egg weight was obtained per initial and average laying hens than in the control and experimental group No.1, respectively. These indicators were minimal in the control group.
The maximum egg production and yield of egg weight in the experimental group No.2 had a significant impact on the conversion of feed to products, the feed efficiency per 10 eggs and 1 kg of egg weight were, respectively, 1.5-5.0 and 2.9-4.5% lower than in the control and the experimental group No.1. The feed efficiency per unit production was the highest in the control group.
Morphological and chemical analysis of eggs showed that, on average, the groups did not differ significantly in the absolute weights of yolk, egg white, eggshell and shell thickness during the experiment. The advantage of the experimental groups Nos.1 and 2 over the control by 0.6-0.7% in the relative weight of the yolk and the lag by 0.3-0.4% in the relative weight of the egg white and by 0.3% in the relative weight of the eggshell were tending. There were practically no differences between the groups in the content of calcium in eggshell, carotenoids, vitamins A, E and B2 in yolk, vitamin B2 in egg white. The existing differences were within the error margin.

Conclusion
Based on the results obtained in two experiments, we can conclude that when keeping laying hens under intermittent LED lighting, the most effective mode was when the sunrise and sunset imitations took place each time the light was switched on and off, and lasted 3 minutes. The smooth switching the light on/off in comparison with the instantaneous switching the light on/off made it possible to increase the livestock livability by 1.9%, egg production and yield of egg weight per initial and average laying hens by 7.3%, 5.8%, 6.5%, 5.1%; as well as to reduce feed efficiency per 10 eggs and 1 kg of egg weight by 5.0% and 4.5%, without significant changes in the quality of eggs.