The effect of monochromatic light-emitting diode light on reproductive traits of laying hens
D ESCRIPTION OF PROBLEM
A s artificial illumination is the only source of light provided to birds in modern poultry houses and light influences both reproductive and production responses in domestic fowl, the duration, intensity, and quality of light have be-come important environmental factors [1]. It is integral to sight, including both visual acuity and color discrimination [2]. Vision is the most important sense for birds, as good eyesight is essential for safe flight, and birds have several adaptations that provide superior visual acuity relative to other vertebrate groups. Birds, un-like humans but similar to fish, amphibians, and reptiles, have 4 types of color receptors in the eye and have more nerve connections between the photoreceptors and the brain [3]. These traits give birds the ability to perceive not only the hu-man-visible range of light but also the UV part of the spectrum, in addition to allowing for the detection of polarized light and magnetic fields. L ight cycles allow the bird to establish rhyth-micity and synchronize many essential func-
? 2014 Poultry Science Association, Inc.
T he effect of monochromatic light-emitting diode light on reproductive traits of laying hens
D iyan L i ,*1L ong Z hang ,*1M ingyao Y ang ,* H uadong Y in ,* H uailiang X u ,*
Jessica S. T rask ,? D avid G. S mith ,? Z hichao Z hang ,* and Q ing Z hu *2
*F arm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Ya’ an, P.R. China 625014;
and ?D epartment of Anthropology, University of California, Davis 95616
P rimary Audience: Live Production Personnel, Breeders, Researchers
S UMMARY
A rtificial illumination is an important exogenous factor in the control of many physiologi-cal and behavioral processes in the management of layers. The objective of this study was to examine the effect of monochromatic light on reproductive traits, fertility, and quality of eggs of local mountainous laying hens of China. Five hundred fifty-two19-wk-old hens were ran-domly divided into 4 groups, with each group consisting of 138 birds. Feed and water were provided ad libitum. Light treatments were control white (mini-incandescent light bulbs), blue (480 nm), green (560 nm), and red (660 nm). Birds maintained under green light produced fewer eggs than other groups. The red light group had a greater egg shape index than other groups and had greater fertility and hatchability than other groups. Egg weight was affected by
light wavelength, but the rate of egg production was not. The ratio between egg components can be changed by the light source without changing the egg weight. Egg quality was the best for hens exposed to the green light.
K ey words:l ight-emitting diode ,r eproductive trait ,f ertility ,e gg quality ,l aying hen
2014 J. Appl. Poult. Res. 23 :367–375
https://www.wendangku.net/doc/3b9104800.html,/ 10.3382/japr.2013-00746
1D iyan Li and Long Zhang contributed equally to this work.
2Corresponding author: z huqingsicau@https://www.wendangku.net/doc/3b9104800.html, at :: on September 2, 2014 https://www.wendangku.net/doc/3b9104800.html,/ Downloaded from
368JAPR: Research Report
tions, including body temperature and various metabolic steps that facilitate feeding and di-gestion. Light, as an environmental factor, con-sists of 3 different aspects that can affect the physical activity of broiler chickens: light inten-sity, color, and the photoperiodic regimen [4]. Color and intensity are important in behavioral modifications, whereas exposure of broilers to darkness is essential to bird health [5]. Color is defined by wavelength and exerts variable ef-fects on flock performance. Light of different wavelengths has varying stimulatory effects on the retina and can result in behavioral changes that will affect growth and development [6]. In previous studies, it was reported that the effect of monochromatic light on growth and develop-ment of broilers is age-related (i.e., green light stimulates growth at an early age, whereas blue light stimulates growth in older birds) [7]. Hens in cool white light produced significantly few-er eggs than those under simulated sunlight in 2 laying cycles. Eggs laid under blue or green light were consistently larger than those under red light [8]. Both blue and green lights were more effective in stimulating testosterone se-cretion and myo?ber growth that resulted in in-creased body growth [9]. Therefore, a possible mechanism for the relationship between light stimulation and egg production exists. The ob-jective of the current study was to investigate the effect of monochromatic light on reproduc-tive traits, fertility, and quality of eggs of Chi-nese local Erlang Mountain chicken.
MATERIALS AND METHODS Bird Treatment
The Erlang Mountain chicken is a cultivated breed that was successfully developed from lo-cal chicken breeds in Sichuan Province, China [10]. A total of 552 hens from the experimental farm for poultry breeding in Sichuan Agricultur-al University were randomly divided into 4 light treatment groups (n = 138) in 3 replicates (n = 46). Birds were housed in individual cages, and for each replicate they were housed in a laying battery [23 cages (length × width × height = 50 × 38 × 35 cm), 1 bird per cage, 2 laying batteries per replicate]. The space between the feed and water was 6 cm. All 552 birds were housed in the same room from hatching to 19 wk of age, at a density of 12 birds/m2 and under cool white
light (400–760 nm) by using a light-emitting
diode system. Photoperiod was 14L:10D from
the first to the nineteenth week. After 19 wk,
the birds were housed under 4 different light treatments in a separate, windowless, fan-ven-
tilated room. Inlets permitting fresh air entry
were opposite the exhaust fans. The fans were controlled jointly by temperature sensors and a
timed program, which ensured similar and ap-
propriate conditions in the rooms. The average temperature in the house was 28°C. This man-
agement protocol in rooms of identical physical
design ensured that environmental conditions
in the rooms were identical. Feed intake was controlled daily according to standard farm hus-
bandry practices and water was provided ad libi-
tum. Arti?cial light systems were placed 10 cm
above the birds using plastic crosses attached to
the ceilings of the rooms. Hens in each group
were exposed to blue light (BL; 480nm), green
light (GL; 560nm), red light (RL; 660nm), or
white light (WL) by a light-emitting diode sys-
tem for 44 wk (from 19 to 63 wk old), respec-
tively. All light sources were equalized to a light
intensity of 15 lx (1.4-ft candle) and applied for
a 16L:8D photoperiod daily. No treatment-relat-
ed mortality was observed during the entire ex-perimental period. The mortalities were less than
5%, and no signi?cant differences were found
among groups. The Animal Welfare Committee
of Sichuan Agricultural University approved the
bird care protocol used for this experiment (No.
DKY-B20110108).
Reproductive Traits
Egg production (including normal eggs,
cracked eggs, soft-shell eggs, and double-yolked
eggs) was recorded daily form 19 to 63 wk of
age and calculated on a hen-day basis. Nine reproductive traits were measured: BW at first
egg, weight of first egg, age at first egg, number
of eggs at 300 d of age, number of eggs at 440
d of age, BW at 300 d of age, egg weight at 300
d of age, egg production at 300 d of age, and
egg production at 441 d of age. Egg weight was measured on an electric balance [11].
Fertility and Hatchability
All eggs for incubation were sorted to remove
cracks, morphological deformities, and dirt be-
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369 LI ET AL.: MONOCHROMATIC LIGHT AND LAYERS
fore acquiring egg weight, egg length, and egg breadth. A total of 412, 400, 400, and 385 hatch-ing eggs were collected at 28 wk of age from the WL, BL, RL, and GL groups, respectively. Fertilized eggs were incubated in a humidi?ed egg incubator at 37°C and 70% RH. Fertility was calculated by total number of fertile eggs divided by total number of eggs set, multiplied by 100. Hatchability of fertile eggs was obtained through the number of chicks hatched divided by total number of fertile eggs, multiplied by 100. Egg weight and chick hatch weight were measured to the nearest 0.01 g using an electron-ic balance [11]. Egg length and egg breadth were measured to the nearest 0.10 cm using a pair of vernier callipers [12].
Egg Quality
Eggs from each group (100/group) were collected at 27 and 60 wk of age, respectively. For this, 20 eggs were randomly collected daily from each group for 5 d. The internal quality of eggs was assessed each day as albumen height by using specialized equipment (QCH albumen height gauge) provided by TSS [13], and Haugh unit was determined using the Haugh unit for-mula [14]. Individual egg and egg component weights were weighed on an electric balance [11]. The eggshells, along with the membranes, were washed with tap water and dried at room temperature for 1 wk. After drying, the eggshells were weighed and the shell thickness was mea-sured using a QCT shell thickness micrometer [13]. Three measurements were taken at the blunt end, sharp end, and equatorial region for each eggshell individually, and the mean of the 3 parts was calculated. Shell strength and shell deformation was measured with a QC-SPA shell and packaging strength analyzer [13]. Egg shell color was measured by using a QCR shell color reflectometer [13].
Plasma Luteinizing Hormone
and Follicle-Stimulating
Hormone Concentrations
When the birds reached 27 wk of age, blood samples (1 mL) were collected from a brachial vein at 1400 h (7 samples were collected under each monochromatic light). Plasma was imme-diately separated by centrifugation at 3,000 × g for 15 min at 4°C and stored at ?20°C for later measurement of gonadotrophin concentrations. Plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured by
using chicken LH-releasing hormone and chick-
en FSH ELISA kit, purchased from Sangon Bio-
tech [15].
Statistical Analysis
Data are shown as least squares means ± SEM. The GLM procedure [16] was used to analyze the effect of monochromatic light on productive performance, fertility, hatchability,
and quality of eggs. The significance of the least squares means was tested with the Duncan’s Multiple Range test. P-values <0.05 were con-sidered signi?cant.
RESULTS AND DISCUSSION
The Effect of Monochromatic Light
on Chicken Reproductive Traits
Body weights, egg weights, and egg num-
bers from 19 to 63 wk of age are presented in
Table 1. A signi?cant difference in BW at 300
d of ag
e was observed in birds among the 4 groups. Birds reared under BL at 300 d o
f age
had a heavier BW compared with other groups,
and egg weight was smaller for them compared
with other groups. Birds reared under GL pro-
duced fewer eggs at both 300 and 440 d of age
than birds reared under other lights. This may
be due to photostimulation of retinal photore-ceptors, which are sensitive to green light and appear to inhibit reproductive activity in birds [17], as well as iodopsin, present in relatively
large amounts in both the chicken and the turkey [18]. In previous studies, green light stimulated growth at an early age, whereas blue light stimu-
lated growth in older birds [19]. Blue-green light stimulates growth in chickens, whereas orange-
red light stimulates reproduction [7]. The results
of the current study are consistent with previous results. Based on our results, we also suggest
that both BL and RL stimulate both growth and reproduction in older birds. This difference may
be due to the fact that other researchers used broilers as a study subject and we used local mountainous laying hens. Also, other research-
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370JAPR: Research Report
ers studied the BW growth from 0 to 46 d old, whereas we observed BW growth from age at first egg to 300 d old.
The effect of monochromatic light on egg number of laying hens from 19 to 63 wk is shown in Figure 1. The GL birds reached their production peak a week later than the other groups and had slightly longer peak production periods. Birds reared under RL produced more eggs than the other groups from age at first egg to 42 wk of age and BL produced fewer eggs. All groups experienced a gradual decrease in total egg number from 42 wk of age. The mean egg production rate from 25 to 48 wk old was 65.45%, making the egg production rate of Sich-uan native chicken relatively low compared with commercial egg-type chicken. Approximately 72.15% of hens started laying eggs at 25 wk of age and all hens started laying eggs by 28 wk of age (data not shown). The egg production curves of the 4 groups showed slight nonsignificant dif-ferences from 28 to 40 wk of age. Birds reared under GL produced fewer eggs than the other groups from 48 to 63 wk of age.
Figure 1. Effect of monochromatic light on egg production rate of laying hens from 19 to 63 wk of age. WL = white light; RL = red light; BL = blue light; GL = green light. at :: on September 2, 2014 https://www.wendangku.net/doc/3b9104800.html,/ Downloaded from
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LI ET AL.: MONOCHROMATIC LIGHT AND LAYERS
In the present study, birds reared under RL and GL produced more cracked eggs, whereas all groups produced more misshapen eggs from age at first egg to 30 wk of age (Figure 2). Soft-shell eggs were mostly produced during the first few weeks of lay. We observed that birds reared under RL often pecked their feathers and were cannibalistic. This result is consistent with pre-vious studies that showed blue light has a calm-ing effect on birds whereas red will enhance feather pecking and cannibalism [19].The Effect of Monochromatic Light on Chicken Egg Quality
The effect of monochromatic light on external and internal quality traits of eggs is illustrated in Table 2 and Figure 2. Egg weights were highest in RL and lowest in BL at both 27 and 40 wk of age. These results support what Pyrzak et al. [8] suggested, that egg weight is affected by the light spectrum but not by the rate of egg production. The egg length in RL was significantly (P < 0.05) longer than those in WL, BL, and GL at 27 wk of age. Egg width in GL was significantly (P < 0.05) longer than those in other lights at 40 wk of
age. It was found that RL results in a longer egg length and egg width, and GL results in a shorter egg length and width. Eggshell strength in GL was better than those in BL and WL at 27 wk of age (Table 3). This result was similar to the re-port of Pyrzak et al. [8] for laying hens in the first laying cycle, in which eggshell strength in green light was significantly better than those in other groups. Nevertheless, at 40 wk of age, our results differed from theirs, as eggshell strength in blue and green light was better than those in red light. The difference could be due to the measurement range; Pyrzak et al. [8] measured in 2 different laying cycles and we measured at 2 time points in the same laying cycle. Eggshell thickness in the GL group was significantly (P < 0.05) thick-er than other groups at 40 wk of age. Eggshell color in GL was significantly (P < 0.05) greater than those in the WL and RL groups at both time points. Therefore, eggshell color is significantly affected by green light. Percent of yolk gain at 27 and 40 wk of age generally increased as the wavelength increased. Relative yolk weight was lowest in the BL treatment at both ages. These results are similar to those in turkey hens [20].
By this result, we confirm Pyrzak et al. [8], who
Figure 2. The effect of monochromatic light on misshapen eggs. Color version available in the online PDF.
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suggested that BL inhibited ovarian develop-ment, resulting in smaller yolks. The percentage of albumen also declined as the wavelength in-creased. This may be due to the greater increase in yolk size relative to wavelength rather than in the change in albumen weight. Therefore, the ra-tio between egg components can be changed by the light source without changing the egg weight. The Effect of Monochromatic Light
on Chicken Fertility and Hatchability Hatching eggs (1,597) were collected from 4 groups at 28 wk of age. The effect of mono-chromatic light on chicken fertility and hatch-ability was presented in Figure 3. The hatching egg weights in the WL and RL groups were signi?cantly (P < 0.05) greater than those in the BL and GL groups (Table 3). Based on the major axis and minor axis, the BL produced smaller eggs, whereas the WL produced larger eggs, a result consistent with Er et al. [21]. The RL group had a greater egg shape index than other groups and showed greater fertility and hatch-ability than other groups, but the difference was not significant (data not shown). Mechanisms of How Monochromatic Light Affects Reproduction in Chickens
The regulation of gonadotropin secretion is very complex. In birds, 2 pivotal neuroendo-crine systems regulate the reproductive cycle: the gonadotropin-releasing hormone-gonado-tropin system and the vasoactive intestinal pep-tide-prolactin system [22, 23]. With respect to biological actions of gonadotropins within the hen ovary, FSH binding to granulosa and theca cell membranes has been reported to decrease as the stage of follicle development approaches the time of ovulation [24–26]. Similar to the mammalian receptor, considerable evidence exists that after interaction of LH with the lu-teinizing hormone/choriogonadotropin receptor, the second messenger signaling mechanism in the hen ovary includes activation of the adeny-lyl cyclase-protein kinase A and phospholipase C-phosphatidylinositol systems [27]. Photo-period serves as a phylogenetically diverse environmental regulatory cue for the control of reproduction [28]. The only light source for chickens in environmentally controlled houses is arti?cial light. Thus, intensity, source, spec-tra, and regimen of light supplementation have become major factors in modern chicken man-agement [29]. Egg production in hens is affected by light wavelength. Hens in cool white light produced significantly fewer eggs than those under simulated sunlight in both laying cycles [8], and eggs laid under blue or green light were consistently larger than those under red light [8]. Light is the dominant environmental factor that regulates melatonin biosynthesis in vertebrates;
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and regardless of whether a species is diurnal-nocturnal or exhibits crepuscular activity, pineal melatonin levels (difference between nighttime and daytime) are high during the dark phase of a natural or imposed illumination cycle [30, 31]. High levels of melatonin can inhibit secretion of LH and FSH from the anterior pituitary gland [32]. Low levels of LH and FSH can inhibit ovulation [33]. From our results we can see that plasma LH and FSH secretion levels under red and blue light are significantly higher (P < 0.05) than under green light during the peak laying pe-riod (27 wk old; Table 4). It seems that chicken raised under long-wavelength light (red light) have higher levels of LH and FSH and produce more eggs than those raised under short-wave-length light (green light).
CONCLUSIONS AND APPLICATIONS
1. Birds reared under GL produce fewer eggs than other groups. The RL group had a greater egg shape index than other groups and showed greater fertility and hatchability than other groups.
2. Egg weight in RL was the heaviest and in GL was the lightest among the 4 types of lights. Yolk weight percentage in RL was smaller than other groups. Addition-ally, the egg quality in GL was the best.
3. The egg production rate of Sichuan na-tive mountainous chicken is relatively low compared with commercial egg-type chicken; however, it can be im-proved much more. If more eggs are needed during the egg-production stage, it is most feasible to first use red light from 19 to 42 wk of age then transfer to blue light. If bigger eggs are needed, we suggest that birds be reared under red light; to improve egg quality birds may be reared under green lights.
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Proc. Natl. Acad. Sci. USA 61:529. Acknowledgments
The authors thank Jesse Grimes (North Carolina State University, Raleigh) and the anonymous reviewers for valu-
able comments. This work was supported by China Agri-
culture Research System (CARS-41; Chengdu, China), and
the Program from Sichuan Province (2011NZ0099-7 and
2011NZ0073). We thank Xiaoling Zhao, Yan Wang, and Yao
Zhang (Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Ya’an, P. R. China) for helping with
data collection.
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