The quantitative models for broiler chicken response to monochromatic, combined, and mixed light-emitting diode light: A meta-analysis

The quantitative models for broiler chicken response to monochromatic, combined, and mixed... ABSTRACT Although many experiments have been conducted to clarify the response of broiler chickens to light-emitting diode (LED) light, those published results do not provide a solid scientific basis for quantifying the response of broiler chickens. This study used a meta-analysis to establish light spectral models of broiler chickens. The results indicated that 455 to 495 nm blue LED light produced the greatest positive response in body weight by 10.66% (BW; P < 0.001) and 515 to 560 nm green LED light increased BW by 6.27% (P < 0.001) when compared with white light. Regression showed that the wavelength (455 to 660 nm) was negatively related to BW change of birds, with a decrease of about 4.9% BW for each 100 nm increase in wavelength (P = 0.002). Further analysis suggested that a combination of the two beneficial light sources caused a synergistic effect. BW was further increased in birds transferred either from green LED light to blue LED light (17.23%; P < 0.001) or from blue LED light to green LED light (17.52%; P < 0.001). Moreover, birds raised with a mixture of green and blue LED light showed a greater BW promotion (10.66%; P < 0.001) than those raised with green LED light (6.27%). A subgroup analysis indicated that BW response to monochromatic LED light was significant regardless of the genetic strain, sex, control light sources, light intensity and regime of LED light, environmental temperature, and dietary ME and CP (P > 0.05). However, there was an interaction between the FCR response to monochromatic LED light with those covariant factors (P < 0.05). Additionally, green and yellow LED light played a role in affecting the meat color, quality, and nutrition of broiler chickens. The results indicate that the optimal ratio of green × blue of mixed LED light or shift to green-blue of combined LED light may produce the optimized production performance, whereas the optimal ratio of green/yellow of mixed or combined LED light may result in the optimized meat quality. INTRODUCTION Environmental manipulation is an effective means to improve poultry production and welfare (Riber et al., 2018; Rodrigues et al., 2017). Among those environmental factors, light plays a vital role in affecting chicken production. Chickens have highly specialized visual systems (Prescott et al., 2003) and possess five cones (Kram et al., 2010). Colored light prevails in the modern broiler industry, including incandescent (Wells, 1971), fluorescent (Wabeck and Skoglund, 1974), UV (Coleman et al., 1977), commercial colored (Proudfoot and Sefton, 1978), filtered-light lamps (Levenick and Leighton, 1988), and light-emitting diodes (LEDs; Pan et al., 2015; Yang et al., 2016a; Yang et al., 2016b). Among those sources, the LED has a long life, specific wavelength, and adjustable intensity. Such advantages make the LED perfect for supporting poultry growth in a controlled environment. Therefore, many poultry producers have switched from incandescent to LED light devices. Rozenboim et al. (1999) demonstrated that 560 nm and 480 nm LED light stimulates broiler chicken body weight. Yang et al. (2016a) recommended using 580 nm LED light to enhance body weight of broiler chickens. Sadrzadeh et al. (2013) reported that red LED light promoted no increase in body weight and that green LED light suppressed it. However, there are still several gaps concerning monochromatic LED light and broiler chicken growth. Results that have been separately published do not provide scientific basis for quantifying the response of broiler chickens. Meta-analysis is a statistical procedure combining the results of independent studies (Lipsey and Wilson, 2001) and can provide a more precise overall estimate of experimental results. Increasing evidence in agricultural production (Challinor et al., 2014; Pittelkow et al., 2015) and poultry production (Remus et al., 2014; Faridi et al., 2015) has confirmed that meta-analysis is a powerful tool to quantify information. Therefore, the present study was conducted to quantify the effects of monochromatic LED light on the production performance, breast muscle meat quality, and nutrition of broiler chickens. Second, we investigated the interaction between monochromatic LED light and covariant factors, including genetic strain and sex of broiler chickens, light intensity and regime of LED, environmental temperature, and diet composition. Third, based on the results of meta-analysis of monochromatic LED light, we further investigated the effect of the combination and mixture of monochromatic LED light on the performance of broiler chickens. MATERIALS AND METHODS Literature Search Strategy A simple search strategy, implemented in May 2017, was conducted in Scopus (www.scopus.com/; 1998 to 2017), and Web of Science (http://webofknowledge.com/WOS; 1998 to 2017). The algorithm included three broad outcome: Light*OR LED* OR Light-emitting Diodes*, and four broad terms: Chick* OR Chicken*OR Poultry* OR Broiler* OR Gallus*. The light sources were confined to monochromatic LED light, combined LED light which indicated birds were transferred from one monochromatic LED light to another during the growth period, and mixed LED light which was fabricated by two different monochromatic LED lights. Eligibility Criteria and Article Selection The assessment of which publications were eligible for inclusion in the meta-analysis was conducted independently by two evaluators. The selection of which articles which were included or excluded in the present study was based a series of criteria developed by our authors. We used LED lights as treatments and white light as the control group. The LED lights included monochromatic blue LED light (455 to 495 nm; Blue), monochromatic green LED light (515 to 560 nm; Green), monochromatic yellow LED light (585 to 600 nm; Yellow), monochromatic red LED light (615 to 660 nm; Red), Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture). The selected articles contained the wavelength of each LED light source. The experiments were limited to rapidly growing broiler chickens. Also, the selected articles needed sufficient data to determine the “effect size” for production parameters (e.g., the number of birds in each treatment and control group, body weight [BW], and feed conversion ratio [FCR]); a measure of variance (SE or SD) or P-value for each effect estimate. The “effect size” is the weighted difference between treatment and control groups means using the standard deviations and bird numbers of control and treatment groups. We only selected peer-reviewed publications (Halevy et al., 1998; Rozenboim et al., 1999, 2004; Cao et al., 2008, 2012; Karakaya et al., 2009; Ke et al., 2011; Kim et al., 2013a, b; Hassan et al., 2013; Mendes et al., 2013; Sultana et al., 2013; Hassan et al., 2014; Guevara et al., 2015; Seo et al., 2015) which investigated the effects of monochromatic LED, combined, and mixed light on the responses of broiler chickens (n = 7,278 observations; Figure 1). Figure 1. View largeDownload slide The procedure of the meta-analysis performed in the present study, including identification, eligibility, data collection, and statistical analysis. ① Mono-LED light: monochromatic blue, green, yellow, and red LED light; Combined LED light: birds were transferred from one monochromatic LED light to another one during the growth period; mixed LED light: fabricated by two different monochromatic LED light. ② body weight (BW; g), feed conversion ratio (FCR; g/g) BW (g), FCR (g/g), muscle per cent (MP; %), meat quality of pH, cook loss (CL; %), water-holding capacity (WHC; %), shear force (SF; kg/cm2), meat color (L*, a*, and b*), and breast protein content (BPC; %) and breast fat content (BFC; %). ③ Wavelength: the wavelength of LED used in the selected articles; Control: control group; Strain: genetic strain; Sex: sex of broiler chickens; Intensity: light intensity of the LED light; Regime: light regime of the LED light; Temp: environmental temperature during growing period; ME: metabolizable energy of diet; CP: crude protein of diet. Figure 1. View largeDownload slide The procedure of the meta-analysis performed in the present study, including identification, eligibility, data collection, and statistical analysis. ① Mono-LED light: monochromatic blue, green, yellow, and red LED light; Combined LED light: birds were transferred from one monochromatic LED light to another one during the growth period; mixed LED light: fabricated by two different monochromatic LED light. ② body weight (BW; g), feed conversion ratio (FCR; g/g) BW (g), FCR (g/g), muscle per cent (MP; %), meat quality of pH, cook loss (CL; %), water-holding capacity (WHC; %), shear force (SF; kg/cm2), meat color (L*, a*, and b*), and breast protein content (BPC; %) and breast fat content (BFC; %). ③ Wavelength: the wavelength of LED used in the selected articles; Control: control group; Strain: genetic strain; Sex: sex of broiler chickens; Intensity: light intensity of the LED light; Regime: light regime of the LED light; Temp: environmental temperature during growing period; ME: metabolizable energy of diet; CP: crude protein of diet. Data Collection The extracted data included LED wavelength, genetic strain, light source of the control group, light intensity, photoperiod, rearing temperature and dietary composition, number of broiler chickens in control, and treatment groups, BW (g), FCR (g intake/g gain), muscle per cent (MP; %), meat quality of pH, cook loss (CL; %), water-holding capacity (WHC; %), shear force (SF; kg/cm2), meat color (L*, a*, and b*), and breast protein content (BPC; %) and breast fat content (BFC; %), measures of variance of responses (SE or SD), and P-values. In cases where data were presented only in figures, values were extracted using Plot Digitizer (http://plotdigitizer.sourceforge.net/). Statistical Analysis Data extracted from included papers were exported into MS Excel 2013 spreadsheets and formatted for meta-analysis. Many articles reported multiple treatment-control comparisons, which were extracted as unique trials for meta-analysis. Stata was used (version 12; StataCorp, College Station, TX) to analyze performance outcomes by weighted mean difference (WMD), which is also called effect size analysis, in which the difference between treatment and control groups means was weighted using the standard deviations of control and treatment groups (1).   \begin{equation} {\rm{WMD\ }} = \mathop \sum \limits_{i = 1}^m {\rm{\omega }}\left( {{{\rm{X}}_{\rm{t}}} - {{\rm{X}}_{\rm{c}}}} \right), \end{equation} (1)in which Xt and Xc represent means for the treatment group (monochromatic LED light) and the control group (white light), respectively, and ω represents a weighting factor estimated by formula (2):   \begin{equation} \omega {\rm{ }} = {\rm{ }}1/v, \end{equation} (2)where ν is the variance. By giving greater weight (ω) to studies whose estimates have greater precision (lower ν), the precision of the pooled estimate and the statistical power are increased. The variance (ν) is calculated by formula (3):   \begin{equation} {\nu} = \, {^{\rm SD_{\rm t}^{2}}} / {_{\rm n_{\rm t}X_{\rm t}^{2}}}, \end{equation} (3)where SDt and SDc are the SD for the treatment group and the control group, respectively, and nt and nc are the sample sizes for the treatment group and the control group, respectively. If the selected articles reported separate estimates of measure of variance (SE or SD) for each group, these were recorded as such. If the selected literature reported a common SE or SD, the estimate was used for both control and treatment groups. Based on the assumption that significant heterogeneity existed among the experiments, random-effects models were conducted for each performance outcome to estimate the effect size, 95% CI, and statistical significance of WMD. A positive value of WMD indicates that the treatment group provides a greater value than the control group. The pooled effect size was considered significantly if it's associated 95% CI (upper and lower 95% CI) did not overlap with zero and randomization tests yielded P-values <0.05. Meta-regression is applied to test whether evidence exists for different effects in different subgroups of trials using the individual WMD for each experiment as the indicator and the associated SE as the measure of variance. (Knapp and Hartung, 2003). The random effects meta-regression with one covariate and additional between trial variance is given by the following equations, which is the regression of WMD on wavelength with weight ω = 1/v (Thomas and Emery, 1969):   \begin{equation} {\rm{WMD}}\sim{\rm{ N}}\left( {\alpha + \beta \times {\rm{wavelength}},v} \right), \end{equation} (4)where WMD is the performance parameters of broilers, wavelength is the value of trial-specific covariate, v is the variance of effect size within trial, β (slope) represents the change in the performance parameters of broilers per unit of change in the covariate wavelength, and α is intercept (i.e., α = 0; WMD — wavelength), N is the performance parameter of broilers if the covariate i equal to zero. Meta-regression analysis was conducted using LED wavelength as covariate and the BW as the parameter of interest. Data were screened for plausible linear relationships between differences in LED wavelength between the treatment and control group and the BW. The effects of monochromatic, combined, and mixed LED light on performance of broiler chickens are displayed in forest plots, using the estimated WMD of products. Points to the left of the line represent a reduction in the parameter, whereas points to the right of the line indicate an increase in the parameter. Each square represents the mean effect size for that study. The upper and lower limits of the line connected to the square represent the upper and lower 95% CI for the effect size. For ease of interpretation, all WMD were transformed and reported as percentage change in performance parameters for the monochromatic, combined, and mixed LED light group relative to the control group. RESULTS The Effect of Monochromatic LED Light on BW of Broiler Chickens Wavelength When averaged across all studies, the BW was increased by 6.29% (95% CI 5.58 to 6.99; P < 0.001) in broiler chickens stimulated with monochromatic LED light in comparison with those stimulated with white light (Figure 2). Figure 2. View largeDownload slide Body weight (BW), feed conversion ratio (FCR), muscle per cent (MP), meat quality of pH, cook loss (CL), water-holding capacity (WHC), shear force (SF), meat color (L*, a*, and b*), and breast protein content (BPC) and breast fat content (BFC) of broiler chickens reared under various wavelength of monochromatic light-emitting diode light (455 to 495 nm blue, 515 to 560 nm green, 585 to 600 nm yellow, and 615 to 660 nm red) compared with white light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 2. View largeDownload slide Body weight (BW), feed conversion ratio (FCR), muscle per cent (MP), meat quality of pH, cook loss (CL), water-holding capacity (WHC), shear force (SF), meat color (L*, a*, and b*), and breast protein content (BPC) and breast fat content (BFC) of broiler chickens reared under various wavelength of monochromatic light-emitting diode light (455 to 495 nm blue, 515 to 560 nm green, 585 to 600 nm yellow, and 615 to 660 nm red) compared with white light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Further analysis indicated that among various monochromatic LED lights, broiler chickens stimulated with monochromatic 455 to 495 nm blue (Blue), 515 to 560 nm green (Green), and 585 to 600 nm yellow LED light (Yellow) significantly increased BW by 10.66% (95% CI 8.79 to 12.53; P < 0.001), 6.27% (95% CI 4.81 to 7.73; P < 0.001), and 4.18% (95% CI 2.53 to 5.85; P < 0.001), respectively, whereas broiler chickens stimulated with 615 to 660 nm red LED light (Red) showed no significant difference in BW (−0.17%; 95% CI −1.48 to 1.13; P = 0.793; Figure 3). Moreover, meta-regression showed a significant negative linear regression of BW change percentage on 455 to 660 nm wavelength (P = 0.002; Figure 4), with a decrease of about 4.9% BW for each 100 nm increase in wavelength. The regression expression was BW change = −0.0489 × wavelength + 32.808. The critical wavelength was at 600 nm, which suggests that shorter wavelengths (<600 nm) promoted the growth of broiler chickens (BW: 4.18% to 10.66%; R2 = 0.5449; P < 0.001; Figure 3), whereas longer wavelengths (>600 nm) had no impact on the growth of broiler chickens (BW: −0.17%; 95% CI −1.48 to 1.13; P = 0.793; Figure 3). Figure 3. View largeDownload slide Forest plots of body weight (BW) for the subgroup analysis of the effect of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red), light source used in the control group, genetic strain, sex on the BW of broiler chickens. Anak: a local rapid-growing strain in Israel; AA: Arbor Acres; XX: a local rapid-growing strain in Republic of Korea. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 3. View largeDownload slide Forest plots of body weight (BW) for the subgroup analysis of the effect of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red), light source used in the control group, genetic strain, sex on the BW of broiler chickens. Anak: a local rapid-growing strain in Israel; AA: Arbor Acres; XX: a local rapid-growing strain in Republic of Korea. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 4. View largeDownload slide Regression of the wavelength-BW change. The linear regression of BW change of broiler chickens on light wavelength. P < 0.05 indicates that the regression model is significant. Figure 4. View largeDownload slide Regression of the wavelength-BW change. The linear regression of BW change of broiler chickens on light wavelength. P < 0.05 indicates that the regression model is significant. Control Lights Either in contrast with incandescent light, fluorescent light, or white LED light, monochromatic LED light showed a statistically significant effect on BW of broiler chickens (P < 0.05). Among the incandescent light, fluorescent light, and white LED light, the white LED light produced the greatest positive response in BW (8.84%; 95% CI 2.22 to 15.47; P = 0.009), whereas fluorescent light produced the lowest positive response in BW (3.63%; 95% CI 2.77 to 4.49; P < 0.001) compared with monochromatic LED light (Figure 3). Genetic Strain In addition, regardless of the broiler genetic strain, monochromatic LED light had a significant effect on the BW of the broiler chickens (P < 0.05; Figure 3). All strains used in the studies showed a significant difference in BW. The BW of the “Anak”, “Arbor Acres”, “XX”, and “Ross” increased by 3.51% (95% CI 2.21 to 5.11; P < 0.001), 8.84% (95% CI 2.22 to 15.47; P = 0.009), 3.81 (95% CI 3.21 to 4.49; P < 0.001), and 7.89% (95% CI 5.40 to 10.39; P < 0.001), respectively. Sex Monochromatic LED light showed a statistically significant effect on BW of male, female, and mixed sex broiler chickens (P < 0.05; Figure 3). For male broilers, monochromatic LED light increase BW 9.54% (95% CI 5.10 to 13.98; P < 0.001). For female broilers, monochromatic LED light increase BW 2.21% (95% CI 1.82 to 2.608; P < 0.001). For mixed sex broilers, monochromatic LED light increase BW 3.82% (95% CI 1.86 to 5.77; P < 0.001). Environmental Conditions and Diet Nutrition As shown in Figure 5, monochromatic LED light with an intensity of 0.1 W/m2 increased BW by 7.29% (95% CI 5.50 to 9.07; P < 0.001), 10 lux could increase BW by 6.15% (95% CI 3.53 to 8.77; P < 0.001), and 15 lux increase BW by 7.53% (95% CI 4.20 to 10.86; P < 0.001). However, monochromatic LED light with an intensity of 45 lux showed no statistical stimulation of BW of broiler chickens (0.51%; 95% CI −0.02 to 1.05; P = 0.062). For light regime, monochromatic LED light with both continuous lighting (≥23 L) and restricted lighting (≤18 L) promoted BW of broiler chickens by 5.8% (95% CI 4.94 to 6.23; P < 0.001) and 4.94% (95% CI 2.13 to 7.75; P < 0.001), compared with white light. The subgroup analyses of temperature indicated that monochromatic LED light had a significant effect on BW of broiler chickens either at 22 °C or 24°C temperature during the growing-out period (22°C: 7.31% [95% CI 6.04 to 8.57; P < 0.001]; 24°C: 7.80% [95% CI 4.47 to 11.12; P < 0.001]). Figure 5. View largeDownload slide Forest plots of BW for the subgroup analysis of the effect of light intensity, photoperiod, and temperature, diet composition (ME and CP) on the BW of broiler chickens. ≥23 L: 23 h light/1 h dark or 24 h light/0 h dark; ≤18 L: 18 h light/6 h dark or 16 h light/8 h dark. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 5. View largeDownload slide Forest plots of BW for the subgroup analysis of the effect of light intensity, photoperiod, and temperature, diet composition (ME and CP) on the BW of broiler chickens. ≥23 L: 23 h light/1 h dark or 24 h light/0 h dark; ≤18 L: 18 h light/6 h dark or 16 h light/8 h dark. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Monochromatic LED light produced a similar increase in BW of broiler chickens fed with diet of higher ME (>3,100 kcal: 3.80%; 95% CI 1.86 to 5.77; P < 0.001) and normal ME (3,100 kcal: 4.09%; 95% CI 3.14 to 5.04; P < 0.001). However, monochromatic LED light produced a greater increase in BW of broiler chickens fed with diet of higher CP (>175 g/kg: 7.61%; 95% CI 3.10 to 12.11; P < 0.001), whereas a lower increase in BW resulted from diet of normal CP (175 g/kg: 4.09%; 95% CI 3.14 to 5.04; P < 0.001). In addition, the meta-analysis indicated that monochromatic LED light had no effect on MP (1.08%; 95% CI −0.71 to 2.89; P = 0.235; Figure 2), regardless of the wavelength of the LED light. The Effect of Monochromatic LED Light on FCR of Broiler Chickens Wavelength The average FCR of broiler chickens stimulated with monochromatic LED light was significantly decreased by −2.68% (95% CI −3.42 to −1.95; P < 0.001) in comparison with those stimulated with white light (Figure 2). Further analysis indicated that the FCR decrease in broiler chickens varied with the wavelength of the monochromatic LED light. The FCR of broiler chickens stimulated with 455 to 495 nm (Blue) and 585 to 600 nm (Yellow) LED light were significantly decreased by −4.47% (95% CI −5.46 to −3.48; P < 0.001) and −3.06% (95% CI −3.57 to −2.04; P < 0.001), respectively, whereas broiler chickens stimulated with 515 to 560 nm (Green) (−0.49%; 95% CI −1.48 to 0.49; P = 0.314) and 515 to 660 nm (Red) LED light (−2.16%; 95% CI −8.80 to 4.40; P = 0.524) showed no significant difference in FCR (Figure 6). Figure 6. View largeDownload slide Forest plots of FCR for the subgroup analysis of the effect of light-emitting diode (LED) light wavelength (455 to 495 nm blue, 515 to 560 nm green, 585 to 600 nm yellow, and 615 to 660 nm red), light source used in the control group, genetic strain, sex on the FCR of broiler chickens. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 6. View largeDownload slide Forest plots of FCR for the subgroup analysis of the effect of light-emitting diode (LED) light wavelength (455 to 495 nm blue, 515 to 560 nm green, 585 to 600 nm yellow, and 615 to 660 nm red), light source used in the control group, genetic strain, sex on the FCR of broiler chickens. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Control Lights The effect sizes of the FCR response to monochromatic LED light (455 to 660 nm) were dependent on the light source used in the control group. Among the incandescent light, fluorescent light, and white LED light, the white LED light produced a significant negative response in FCR (−11.72%; 95% CI −20.96 to −2.33; P = 0.013), whereas the incandescent light (−0.09%; 95% CI −6.71 to 6.71; P = 0.975) and fluorescent light (−0.77%; 95% CI −1.64 to 0.00; P = 0.066) produced no response in FCR when compared with monochromatic LED light (Figure 6). Genetic Strain In addition, the effect sizes of the FCR response to monochromatic LED light were also dependent on the broiler genetic strain used in the studies. All strains used in the studies showed a significant difference in BW. The BW of the “Anak” and “Arbor Acres” strains could be decreased by −4.10 (95% CI −5.12 to −2.80; P < 0.001) and −11.72% (95% CI −20.96 to −2.33; P = 0.013), respectively, whereas no significant effects were observed for the “XX” (−2.70%; 95% CI −6.96 to 12.61; P = 0.589) and “Ross” (−0.77%; 95% CI −1.64 to 0.00; P = 0.066; Figure 6) strains. Sex The effect sizes of the FCR response to monochromatic LED light were dependent on the sex broiler chickens. For male broilers, monochromatic LED light could decrease FCR by −4.70% (95% CI −5.61 to -3.74; P < 0.001). For female broilers, monochromatic LED light could decrease FCR by −1.75% (95% CI −2.35 to −1.15; P < 0.001). However, for mixed sex broilers, monochromatic LED light showed no effect on the FCR of the broiler chickens (2.70%; 95% CI −7.09 to 12.52; P = 0.589). Environmental Conditions and Diet Nutrition As shown in Figure 7, the subgroup analyses of light. intensity indicated that monochromatic LED light had a similar effect on FCR of broiler chickens exposed to 0.1 W/m2 and 10 lux (0.1 W/m2: −2.34% [95% CI −3.45 to −1.17; P < 0.001]; 10 lux: −1.75% [95% CI −2.35 to −1.15; P < 0.001]). For light regime, continuous lighting (≥23 L) of monochromatic LED light decreased FCR of broiler chickens by −3.98 (95% CI −4.87 to −3.09; P < 0.001). However, restricted lighting (≤18 L) of monochromatic LED light exerted a little effect on FCR (−0.38%; 95% CI −1.13 to 0.32; P = 0.295). Monochromatic LED light could decrease FCR of 24°C-treated broilers by −0.71% (95% CI −2.54 to −0.88; P < 0.001), whereas monochromatic LED light had no influence on FCR of 22°C-treated broilers (0.32%; 95% CI −7.17 to 7.85; P = 0.933). As shown in Figure 5, the effect of monochromatic LED light on FCR had no statistical correlation with ME and CP of diet. Figure 7. View largeDownload slide Forest plots of FCR for the subgroup analysis of the effect of light intensity, photoperiod, temperature, diet composition (ME and CP) on the FCR of broiler chickens. The number of observations in each category is displayed in parentheses. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 7. View largeDownload slide Forest plots of FCR for the subgroup analysis of the effect of light intensity, photoperiod, temperature, diet composition (ME and CP) on the FCR of broiler chickens. The number of observations in each category is displayed in parentheses. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. The Effect of Monochromatic LED Light on Breast Muscle Meat Characteristics of Broiler Chickens Breast Muscle Meat Color Monochromatic LED light exhibited no effect on the L* value of breast meat (1.02%; 95% CI −0.61 to 2.67; P = 0.22; Figure 2): not 455 to 495 nm (Blue) LED light (−2.33%; 95% CI −11.41 to 6.76; P = 0.617), 515 to 560 nm (Green) LED light (1.00%; 95% CI −5.36 to 7.36; P = 0.758), 585 to 600 nm (Yellow) LED light (4.22%; 95% CI −4.41 to 12.86; P = 0.495), or 615 to 660 nm (Red) LED light (2.95%; 95% CI −5.51 to 11.39; P = 0.495; Table 1). The same situation was also observed for the a* value (1.81%; 95% CI −1.03 to 4.25; P = 0.976; Table 1) and the L* value of breast meat. However, although they did not produce the same overall effects of the monochromatic LED light, yellow and red LED lights significantly increased the b* value of the breast meat (Yellow: −3.69%; 95% CI 0.65 to 6.62; P = 0.016; Red: 2.26%; 95% CI 0.75 to 3.77; P = 0.003) (Table 1). Table 1. The effects of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red) on meat quality of pH, cook loss (CL), water-holding capacity (WHC), shear force (SF), meat color (L*, a*, and b*), and breast protein content (BPC) and breast fat content (BFC) compared with white light. Data are expressed as means ± 95% confidence interval (CI).1 Variable  pH  CL  WHC  SF  L*  a*  b*  BPC  BFC  Blue  Mean  1.86  −14.22*  −5.23*  −10.70*  −2.33  4.51  −11.43  0.043  0.00    LCI  −1.01  −25.43  −9.19  −18.42  −11.41  −6.12  −26.52  −3.61  −35.90    UCI  4.56  −2.99  −1.34  −2.97  6.76  7.92  3.48  3.65  35.90    P-value  0.216  0.013  0.009  0.007  0.617  0.978  0.132  0.988  0.998  Green  Mean  1.69*  −9.90*  −7.83*  13.96*  1.00  −12.45  5.49  0.087  5.90    LCI  1.02  −14.58  −11.50  2.91  −5.36  −26. 94  −14.97  −5.17  −30.41    UCI  2.20  −5.15  −4.28  25.02  7.36  24.11  26.11  5.34  41.76    P-value  <0.001  <0.001  <0.001  0.014  0.758  0.923  0.597  0.974  0.754  Yellow  Mean  0.17  −3.50  −6.32*  −10.99  4.22  26.95  3.69*  −1.95*  34.13*    LCI  −1.69  −9.55  −10.99  −27.74  −4.41  −68.93  0.65  −3.83  11.38    UCI  1.86  2.55  −1.37  6.04  12.86  72.12  6.62  −0.09  57.48    P-value  0.924  0.648  0.011  0.205  0.495  0.941  0.016  0.039  0.003  Red  Mean  −1.98*  1.45  −8.04  6.73*  2.95  44.44  2.26*  −2.08*  30.61    LCI  −3.63  −4.79  −20.30  0.28  −5.51  −81.66  0.75  −2.87  −36.56    UCI  −0.49  7.76  4.42  13.18  11.38  90.56  3.77  −1.35  97.79    P-value  0.014  0.255  0.205  0.042  0.338  0.919  0.003  <0.001  0.373  Variable  pH  CL  WHC  SF  L*  a*  b*  BPC  BFC  Blue  Mean  1.86  −14.22*  −5.23*  −10.70*  −2.33  4.51  −11.43  0.043  0.00    LCI  −1.01  −25.43  −9.19  −18.42  −11.41  −6.12  −26.52  −3.61  −35.90    UCI  4.56  −2.99  −1.34  −2.97  6.76  7.92  3.48  3.65  35.90    P-value  0.216  0.013  0.009  0.007  0.617  0.978  0.132  0.988  0.998  Green  Mean  1.69*  −9.90*  −7.83*  13.96*  1.00  −12.45  5.49  0.087  5.90    LCI  1.02  −14.58  −11.50  2.91  −5.36  −26. 94  −14.97  −5.17  −30.41    UCI  2.20  −5.15  −4.28  25.02  7.36  24.11  26.11  5.34  41.76    P-value  <0.001  <0.001  <0.001  0.014  0.758  0.923  0.597  0.974  0.754  Yellow  Mean  0.17  −3.50  −6.32*  −10.99  4.22  26.95  3.69*  −1.95*  34.13*    LCI  −1.69  −9.55  −10.99  −27.74  −4.41  −68.93  0.65  −3.83  11.38    UCI  1.86  2.55  −1.37  6.04  12.86  72.12  6.62  −0.09  57.48    P-value  0.924  0.648  0.011  0.205  0.495  0.941  0.016  0.039  0.003  Red  Mean  −1.98*  1.45  −8.04  6.73*  2.95  44.44  2.26*  −2.08*  30.61    LCI  −3.63  −4.79  −20.30  0.28  −5.51  −81.66  0.75  −2.87  −36.56    UCI  −0.49  7.76  4.42  13.18  11.38  90.56  3.77  −1.35  97.79    P-value  0.014  0.255  0.205  0.042  0.338  0.919  0.003  <0.001  0.373  1SE = (UCI − LCI)/2Z, in which the Z score is equal to 1.96, when α = 0.05. Effect sizes were considered significant if the 95% CI (upper 95% CI [UCI] and lower 95% CI [LCI]) did not overlap with 0. *P < 0.05. View Large Table 1. The effects of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red) on meat quality of pH, cook loss (CL), water-holding capacity (WHC), shear force (SF), meat color (L*, a*, and b*), and breast protein content (BPC) and breast fat content (BFC) compared with white light. Data are expressed as means ± 95% confidence interval (CI).1 Variable  pH  CL  WHC  SF  L*  a*  b*  BPC  BFC  Blue  Mean  1.86  −14.22*  −5.23*  −10.70*  −2.33  4.51  −11.43  0.043  0.00    LCI  −1.01  −25.43  −9.19  −18.42  −11.41  −6.12  −26.52  −3.61  −35.90    UCI  4.56  −2.99  −1.34  −2.97  6.76  7.92  3.48  3.65  35.90    P-value  0.216  0.013  0.009  0.007  0.617  0.978  0.132  0.988  0.998  Green  Mean  1.69*  −9.90*  −7.83*  13.96*  1.00  −12.45  5.49  0.087  5.90    LCI  1.02  −14.58  −11.50  2.91  −5.36  −26. 94  −14.97  −5.17  −30.41    UCI  2.20  −5.15  −4.28  25.02  7.36  24.11  26.11  5.34  41.76    P-value  <0.001  <0.001  <0.001  0.014  0.758  0.923  0.597  0.974  0.754  Yellow  Mean  0.17  −3.50  −6.32*  −10.99  4.22  26.95  3.69*  −1.95*  34.13*    LCI  −1.69  −9.55  −10.99  −27.74  −4.41  −68.93  0.65  −3.83  11.38    UCI  1.86  2.55  −1.37  6.04  12.86  72.12  6.62  −0.09  57.48    P-value  0.924  0.648  0.011  0.205  0.495  0.941  0.016  0.039  0.003  Red  Mean  −1.98*  1.45  −8.04  6.73*  2.95  44.44  2.26*  −2.08*  30.61    LCI  −3.63  −4.79  −20.30  0.28  −5.51  −81.66  0.75  −2.87  −36.56    UCI  −0.49  7.76  4.42  13.18  11.38  90.56  3.77  −1.35  97.79    P-value  0.014  0.255  0.205  0.042  0.338  0.919  0.003  <0.001  0.373  Variable  pH  CL  WHC  SF  L*  a*  b*  BPC  BFC  Blue  Mean  1.86  −14.22*  −5.23*  −10.70*  −2.33  4.51  −11.43  0.043  0.00    LCI  −1.01  −25.43  −9.19  −18.42  −11.41  −6.12  −26.52  −3.61  −35.90    UCI  4.56  −2.99  −1.34  −2.97  6.76  7.92  3.48  3.65  35.90    P-value  0.216  0.013  0.009  0.007  0.617  0.978  0.132  0.988  0.998  Green  Mean  1.69*  −9.90*  −7.83*  13.96*  1.00  −12.45  5.49  0.087  5.90    LCI  1.02  −14.58  −11.50  2.91  −5.36  −26. 94  −14.97  −5.17  −30.41    UCI  2.20  −5.15  −4.28  25.02  7.36  24.11  26.11  5.34  41.76    P-value  <0.001  <0.001  <0.001  0.014  0.758  0.923  0.597  0.974  0.754  Yellow  Mean  0.17  −3.50  −6.32*  −10.99  4.22  26.95  3.69*  −1.95*  34.13*    LCI  −1.69  −9.55  −10.99  −27.74  −4.41  −68.93  0.65  −3.83  11.38    UCI  1.86  2.55  −1.37  6.04  12.86  72.12  6.62  −0.09  57.48    P-value  0.924  0.648  0.011  0.205  0.495  0.941  0.016  0.039  0.003  Red  Mean  −1.98*  1.45  −8.04  6.73*  2.95  44.44  2.26*  −2.08*  30.61    LCI  −3.63  −4.79  −20.30  0.28  −5.51  −81.66  0.75  −2.87  −36.56    UCI  −0.49  7.76  4.42  13.18  11.38  90.56  3.77  −1.35  97.79    P-value  0.014  0.255  0.205  0.042  0.338  0.919  0.003  <0.001  0.373  1SE = (UCI − LCI)/2Z, in which the Z score is equal to 1.96, when α = 0.05. Effect sizes were considered significant if the 95% CI (upper 95% CI [UCI] and lower 95% CI [LCI]) did not overlap with 0. *P < 0.05. View Large Breast Muscle Meat Quality For pH value and SF, no significant effects were observed in broiler chickens stimulated with the monochromatic LED light in contrast with those stimulated with white light (pH: 0.84% [95% CI −0.34 to 1.87; P = 0.139]; SF: −0.34% [95% CI −3.75 to 3.24; P = 0.89]; Figure 2). However, significant effects were found in CL and WHC in broiler chickens stimulated with the monochromatic LED light in contrast with those stimulated with white light (CL: −7.73% [95% CI −11.25 to −4.21; P < 0.001]; WHC: −6.64% [95% CI −8.93 to −4.35; P < 0.001]; Figure 2). Further meta-analysis indicated that 455 to 495 nm (Blue) LED light significantly decreased the CL (−14.22%; 95% CI −25.43 to −2.99; P = 0.013), WHC (−5.23%; 95% CI −9.19 to −1.34; P = 0.009), and SF (−10.70%; 95% CI −18.42 to −2.97; P = 0.007) in breast meat compared with white light (Table 1). Further, 515 to 560 nm (Green) LED light significantly decreased the CL (−9.90%; 95% CI −14.58 to −5.15; P < 0.001) and WHC (−7.83%; 95% CI −11.50 to −4.28; P < 0.001), whereas it increased the pH value (1.69%; 95% CI 1.02 to 2.20; P < 0.001) and SF (13.96%; 95% CI 2.91 to 25.02; P = 0.014) in breast meat compared with white light. The 585 to 600 nm (Yellow) LED light had a negative effect on WHC (−6.32%; 95% CI −10.99 to −1.37; P = 0.011), whereas 615 to 660 nm (Red) LED light had a positive effect on SF (6.73%; 95% CI 0.28 to 13.18; P = 0.042) in breast meat compared with white light. Breast Muscle Meat Nutrition No significant difference was observed in BPC of broiler chickens stimulated with monochromatic LED light (−0.87%; 95% CI −2.74 to 1.00; P = 0.357; Figure 2), in contrast with white light. However, 585 to 600 nm (Yellow) (−1.95%; 95% CI −3.83 to −0.09; P = 0.039) and 615 to 660 nm (Red) LED light (−2.08%; 95% CI −2.87 to −1.35; P < 0.001) caused a negative response to BPC (Table 1). For BFC, monochromatic LED light had an overall effect on BFC (10.47%; 95% CI 0.46 to 20.48; P = 0.043; Figure 2). Moreover, 585 to 600 nm (Yellow) LED light produced the greatest positive response in BFC (34.13%; 95% CI 11.38 to 57.48; P = 0.003). The Effect of Combined and Mixed LED Light on Performance of Broiler Chickens The effect of combined and mixed LED light on BW of broiler chickens are shown in Figure 8. When averaged across all studies, BW was further increased in broiler chickens stimulated with Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture) in comparison with those stimulated with white light (G-B combination: 17.23% [95% CI 16.89 to 17.58; P < 0.001]; B-G combination: 17.52% [95% CI 17.06 to 17.97; P < 0.001]; G × B mixture: 10.66% [95% CI 7.29 to 14.02; P < 0.001]). Figure 8. View largeDownload slide Body weight (BW) of broiler chickens reared under 455 to 495 nm blue LED light (Blue), 515 to 560 nm green LED light (Green), Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture) compared with white light. G-B combination, birds from monochromatic green LED light were transferred to monochromatic blue LED light. B-G combination, birds from monochromatic blue LED light were transferred to monochromatic green LED light. G × B mixture, birds were exposed to Green × Blue mixed LED light, which was fabricated by monochromatic green and blue LED light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 8. View largeDownload slide Body weight (BW) of broiler chickens reared under 455 to 495 nm blue LED light (Blue), 515 to 560 nm green LED light (Green), Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture) compared with white light. G-B combination, birds from monochromatic green LED light were transferred to monochromatic blue LED light. B-G combination, birds from monochromatic blue LED light were transferred to monochromatic green LED light. G × B mixture, birds were exposed to Green × Blue mixed LED light, which was fabricated by monochromatic green and blue LED light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. The average FCR of broiler chickens stimulated with Green-Blue combined LED light, Blue-Green combined LED light, and Green × Blue mixed LED light was further decreased in comparison with those stimulated with white light (G-B combination: −9.61% [95% CI −12.94 to −6.28; P < 0.001]; B-G combination: −11.70% [95% CI −15.40 to −7.99; P < 0.001]; G × B mixture: −4.00% [95% CI −5.14 to −2.86; P < 0.001]; Figure 9). Figure 9. View largeDownload slide Feed conversion ratio (FCR) of broiler chickens reared under 455 to 495 nm blue LED light (Blue), 515 to 560 nm green LED light (Green), Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture) compared with white light. G-B combination, birds from monochromatic green LED light were transferred to monochromatic blue LED light. B-G combination, birds from monochromatic blue LED light were transferred to monochromatic green LED light. G × B mixture, birds were exposed to Green × Blue mixed LED light, which was fabricated by monochromatic green and blue LED light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 9. View largeDownload slide Feed conversion ratio (FCR) of broiler chickens reared under 455 to 495 nm blue LED light (Blue), 515 to 560 nm green LED light (Green), Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture) compared with white light. G-B combination, birds from monochromatic green LED light were transferred to monochromatic blue LED light. B-G combination, birds from monochromatic blue LED light were transferred to monochromatic green LED light. G × B mixture, birds were exposed to Green × Blue mixed LED light, which was fabricated by monochromatic green and blue LED light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. DISCUSSION Due to the potential advantages of LEDs, multiple studies have been conducted to investigate the potential application of LED light in poultry husbandry. However, the quantification of the relationships between LED light and the response of broiler chickens still have not been identified. While there have been attempts to summarize the relationships between LED light and the response of broiler chickens (Halevy et al., 2006; Parvin et al., 2014a,b), those studies were conducted under different conditions and the results are sometimes contradictory and inconclusive. Therefore, it is hard to draw general conclusions from the results. This study used a meta-analysis to model the response of the broiler chickens to monochromatic LED light. Further to quantify the effect of the combination and mixture of monochromatic LED light on the response of the broiler chickens. Final, we investigated the interactions between monochromatic LED light and covariant factors. We hypothesize that a light spectrum with shorter wavelengths results in beneficial growth whereas that with longer wavelengths has a negative effect on growth. Our meta-analysis confirmed this hypothesis and supports previous reports by Olanrewaju et al. (2015) and Huth and Archer (2015). Olanrewaju et al. (2015) evaluated the effects of color temperatures of LED lamps on growth performance of broiler chickens and showed that the BW gains of broiler chickens stimulated with incandescent light (2,010 K) were statistically similar to those of broiler chickens stimulated with warm LED light (2,700 K), but were statistically lower than those of broiler chickens stimulated with cool LED light (5,000 K). This is possibly caused by the difference in spectrum between warm and cool LEDs. Warm cool LEDs both have two large gradual peaks, but they are not the same. Warm LED has a major peak at 630 nm (red light) and a minor peak at 460 nm (blue light). A cool LED has a major peak at 460 nm (blue light) and a minor peak at 520 to 590 nm (green to yellow light; Olanrewaju et al., 2015). Based on the negative relationship between light wavelength and BW change of broiler chickens found in the present study, it is conceivable that the growth promotion in broiler chickens was attributable to an increase in the blue portion of the spectrum in the cool LED. The above analysis suggests that it is possible to optimize broiler chicken growth by giving an optimal ratio of blue/green light. To confirm this hypothesis, the present study found that BW was further increased in broiler chickens transferred either from green LED light to blue LED light (G-B combination: 17.23%; P < 0.001) or from blue LED light to green LED light (B-G combination: 17.52%; P < 0.001). Broiler chickens exposed to the mixture of green and blue LED light showed a greater BW promotion (G × B mixture: 10.66%; P < 0.001) than those exposed to green LED light (Green: 6.27%). The present study found that FCR was significantly improved by 455 to 495 nm (Blue) LED light (−4.47%; P < 0.001), whereas no effect was observed for 515 to 560 nm (Green) LED light (−0.49%; P = 0.314) compared with white light. Moreover, further analysis indicated that FCR was further improved in broiler chickens transferred either from green LED light to blue LED light (G-B combination: −9.61%; P < 0.001) or from blue LED light to green LED light (B-G combination: −11.70%; P < 0.001). Broiler chickens exposed to a mixture of green and blue LED light showed a similar FCR promotion (G × B mixture: −4.00%; P < 0.001) with those exposed to blue LED light (Blue: −4.47%). Previous behavior tests suggested that red- or white light-treated broiler chickens expressed more aggressive activity (Prayitno et al., 1997) and that blue light-treated broiler chickens were calmer than those treated by white light (Rodenboog, 2001). The blue light also has been found to decrease cortisol concentrations in serum compared to white light, suggesting blue light alleviates the stress response in broiler chickens (Xie et al., 2008). The decreased stress in broiler chickens (Abdo et al., 2017) caused by blue light might use less energy in response to stressors, which decreased the “waste energy” and might increase the amount of energy for growth stimulation. Taken together, the results of the behavior and stress tests might explain the better FCR in broiler chickens stimulated with blue light. This meta-analysis based on published data quantitatively identified the response of the broiler chickens to monochromatic, combined, and mixed LED light. Subgroup analysis indicated that BW responses to monochromatic LED light were statistically significant regardless of the genetic strain and sex of broiler chickens, control light sources, light intensity and regime of LED light, environmental temperature, and dietary ME and CP. However, FCR responses to monochromatic LED light interacted with the genetic strain and sex of broiler chickens, control light sources, light intensity and regime of LED light, environmental temperature, and dietary ME and CP. Monochromatic blue LED light promoted better performance of the main production performance (BW and FCR) of broiler chickens compared with white light. The combination and mixture of the monochromatic blue and green LED light could further improve the production performance of broiler chickens. Monochromatic green and yellow LED light played a role in affecting the meat color quality and nutrition of broiler chickens (Table 2). The further study should be designed to optimize broiler production by the optimal ratio of green × blue of mixed LED light or a shift to green-blue combined LED light, whereas optimize the meat quality and nutrition by the optimal ratio of green/yellow of mixed or combined LED light. Table 2. The summary of the effect of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red) on performance of broiler chickens.     View Large Table 2. The summary of the effect of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red) on performance of broiler chickens.     View Large Footnotes 1 This work was supported by the National Key Research and Development Program of China (NO. 2017YFB0404000). REFERENCES Abdo S. E., Elkassas S., Elnahas A. F., Mahmoud S. 2017. Modulatory effect of monochromatic blue light on heat stress response in commercial broilers. Sci Rep . 4: 1361– 1370. Cao J., Liu W., Wang Z., Xie D., Jia L., Chen Y.. 2008. Green and blue monochromatic lights promote growth and development of broilers via stimulating testosterone secretion and myofiber growth. The Journal of Applied Poultry Research . 17: 211– 218. Google Scholar CrossRef Search ADS   Cao J., Wang Z., Dong Y., Zhang Z., Li J., Li F., Chen Y.. 2012. Effect of combinations of monochromatic lights on growth and productive performance of broilers. Poultry Science . 91: 3013– 3018. Google Scholar CrossRef Search ADS PubMed  Challinor A. J., Watson J., Lobell D. B., Howden S. M., Smith D. R., Chhetri N.. 2014. A meta-analysis of crop yield under climate change and adaptation. Nature Clim Change  4: 287– 291. Google Scholar CrossRef Search ADS   Coleman M., McDaniel G., Neeley W., Ivey W.. 1977. Physical comparisons of lighted incubation in avian eggs. Poultry Science . 56: 1421– 1425. Google Scholar CrossRef Search ADS   Faridi A., Gitoee A., France J.. 2015. A meta-analysis of the effects of nonphytate phosphorus on broiler performance and tibia ash concentration. Poultry Science . 94: 2753– 2762. Google Scholar CrossRef Search ADS PubMed  Guevara B., Pech P., Zamora B., Navarrete S., Magaña S. 2015. Performance of broilers reared under monochromatic light emitting diode supplemental lighting. Rev. Bras. Cienc. Avic. . 17: 553– 558. Google Scholar CrossRef Search ADS   Halevy O., Biran I., Rozenboim I.. 1998. Various light source treatments affect body and skeletal muscle growth by affecting skeletal muscle satellite cell proliferation in broilers. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology  120: 317– 323. Google Scholar CrossRef Search ADS   Halevy O., Yahav S., Rozenboim I.. 2006. Enhancement of meat production by environmental manipulations in embryo and young broilers. World's Poult. Sci. J . 62: 485– 497. Hassan R., Sultana S., Choe H. S. 2013. A comparison of monochromatic and mixed led light color on performance, bone mineral density, meat and blood properties, and immunity of broiler chicks. J. Poult. Sci . 51: 195– 201. Hassan M. R., Sultana S., Choe H. S., Ryu K. S.. 2014. A comparison of monochromatic and mixed LED light color on performance, bone mineral density, meat and blood properties, and immunity of broiler chicks. J. Poult. Sci . 51: 195– 201. Google Scholar CrossRef Search ADS   Huth J. C., Archer G. S.. 2015. Comparison of two LED light bulbs to a dimmable CFL and their effects on broiler chicken growth, stress, and fear. Poultry Science . 94: 2027– 2036. Google Scholar CrossRef Search ADS PubMed  Karakaya M., Parlat S., Yilmaz M., Yildirim I., Ozalp B.. 2009. Growth performance and quality properties of meat from broiler chickens reared under different monochromatic light sources. British Poultry Science . 50: 76– 82. Google Scholar CrossRef Search ADS PubMed  Ke Y., Liu W., Wang Z., Chen Y.. 2011. Effects of monochromatic light on quality properties and antioxidation of meat in broilers. Poultry Science . 90: 2632– 2637. Google Scholar CrossRef Search ADS PubMed  Kim M. J., Parvin R., Mushtaq M. M. H., Hwangbo J., Kim J. H., Na J. C., Kim D. W., Kang H. K., Kim C. D., Cho K. O., Yang C. B., Choi H. C.. 2013. Growth performance and hematological traits of broiler chickens reared under assorted monochromatic light sources. Poultry Science . 92: 1461– 1466. Google Scholar CrossRef Search ADS PubMed  Knapp G., Hartung J.. 2003. Improved tests for a random effects meta-regression with a single covariate. Statist. Med.  22: 2693– 2710. Google Scholar CrossRef Search ADS   Kram Y. A., Mantey S., Corbo J. C.. 2010. Avian cone photoreceptors tile the retina as five independent, self-organizing mosaics. Plos One  5: e8992. Google Scholar CrossRef Search ADS PubMed  Levenick C., Leighton A.. 1988. Effects of Photoperiod and Filtered Light on Growth, Reproduction, and Mating Behavior of Turkeys.: 1. Growth Performance of Two Lines of Males and Females. Poultry Science . 67: 1505– 1513. Google Scholar CrossRef Search ADS PubMed  Lipsey M. W., Wilson D. B.. 2001. Practical meta-analysis . Sage Publications, Inc. Mendes A. S., Paixão S. J., Restelatto R., Morello G. M., de Moura D. J., Possenti J. C.. 2013. Performance and preference of broiler chickens exposed to different lighting sources. The Journal of Applied Poultry Research . 22: 62– 70. Google Scholar CrossRef Search ADS   Olanrewaju H., Purswell J., Maslin W., Collier S., Branton S.. 2015. Effects of color temperatures (kelvin) of LED bulbs on growth performance, carcass characteristics, and ocular development indices of broilers grown to heavy weights. Poultry Science . 94: 338– 344. Google Scholar CrossRef Search ADS PubMed  Pan J., Yang Y., Yang B., Dai W., Yu Y.. 2015. Human-friendly light-emitting diode source stimulates broiler growth. Plos One . 10: e0135330. Google Scholar CrossRef Search ADS PubMed  Parvin R., Mushtaq M., Kim M., Choi H.. 2014a. Light emitting diode (LED) as a source of monochromatic light: A novel lighting approach for behaviour, physiology and welfare of poultry. Worlds Poultry Science Journal . 70: 543– 556. Google Scholar CrossRef Search ADS   Parvin R., Mushtaq M., Kim M., Choi H.. 2014b. Light emitting diode (LED) as a source of monochromatic light: A novel lighting approach for immunity and meat quality of poultry. Worlds Poultry Science Journal . 70: 557– 562. Google Scholar CrossRef Search ADS   Pittelkow C. M., Liang X., Linquist B. A., van Groenigen K. J., Lee J., Lundy M. E., van Gestel N., Six J., Venterea R. T., van Kessel C.. 2015. Productivity limits and potentials of the principles of conservation agriculture. Nature  517: 365– 368. Google Scholar CrossRef Search ADS PubMed  Prayitno D., Phillips C., Omed H.. 1997. The effects of color of lighting on the behavior and production of meat chickens. Poultry Science . 76: 452– 457. Google Scholar CrossRef Search ADS PubMed  Prescott N., Wathes C. M., Jarvis J.. 2003. Light, vision and the welfare of poultry. Animal Welfare  12: 269– 288. Proudfoot F., Sefton A.. 1978. Feed texture and light treatment effects on the performance of chicken broilers. Poultry Science . 57: 408– 416. Google Scholar CrossRef Search ADS   Remus A., Hauschild L., Andretta I., Kipper M., Lehnen C. R., Sakomura N. K.. 2014. A meta-analysis of the feed intake and growth performance of broiler chickens challenged by bacteria. Poult. Sci . 93: 1149– 1158. Google Scholar CrossRef Search ADS PubMed  Riber A. B., Ha V. D. W., de Jong I. C., Steenfeldt S. 2018. Review of environmental enrichment for broiler chickens. Poult. Sci . 97: 378– 396. Google Scholar CrossRef Search ADS PubMed  Rodenboog H. 2001. Sodium, green, blue, cool or warm-white light. World Poult . 17: 22– 23. Rodrigues I., Svihus B., Bedford M. R., Gous R., Choct M. 2017. Intermittent lighting improves resilience of broilers during the peak phase of sub-clinical necrotic enteritis infection. Poult. Sci . 97: 438– 446. Google Scholar CrossRef Search ADS   Rozenboim I., Biran I., Chaiseha Y., Yahav S., Rosenstrauch A., Sklan D., Halevy O.. 2004. The effect of a green and blue monochromatic light combination on broiler growth and development. Poultry Science . 83: 842– 845. Google Scholar CrossRef Search ADS PubMed  Rozenboim I., Biran I., Uni Z., Robinzon B., Halevy O.. 1999. The effect of monochromatic light on broiler growth and development. Poultry Science . 78: 135– 138. Google Scholar CrossRef Search ADS PubMed  Sadrzadeh A., Brujeni G. N., Livi M., Nazari M. J., Sharif M. T., Hassanpour H., Haghighi N.. 2013. Cellular immune response of infectious bursal disease and Newcastle disease vaccinations in broilers exposed to monochromatic lights. Afr. J. Biotechnol . 10: 9528– 9532. Seo H.-S., Kang M., Yoon R.-H., Roh J.-H., Wei B., Ryu K. S., Cha S.-Y., Jang H.-K.. 2015. Effects of various LED light colors on growth and immune response in broilers. Jpn. Poult. Sci. . 53: 76– 81. Google Scholar CrossRef Search ADS   Sultana S., Hassan M., Choe H. S., Ryu K. S.. 2013. The effect of monochromatic and mixed LED light colour on the behaviour and fear responses of broiler chicken. Avian Biol Res . 6: 207– 214. Google Scholar CrossRef Search ADS   Thomas J. W., Emery R. S.. 1969. Additive nature of sodium bicarbonate and magnesium oxide on milk fat concentrations of milking cows fed restricted-roughage rations. Journal of Dairy Science . 52: 1762– 1769. Google Scholar CrossRef Search ADS   Wabeck C., Skoglund W.. 1974. Influence of Radiant Energy from Fluorescent Light Sources on Growth, Mortality, and Feed Conversion of Broilers. Poultry Science . 53: 2055– 2059. Google Scholar CrossRef Search ADS PubMed  Wells R. 1971. A comparison of red and white light and high and low dietary protein regimes for growing pullets. British Poultry Science . 12: 313– 325. Google Scholar CrossRef Search ADS PubMed  Xie D., Wang Z. X., Dong Y. L., Cao J., Wang J. F., Chen J. L., Chen Y. X.. 2008. Effects of monochromatic light on immune response of broilers. Poultry Science . 87: 1535– 1539. Google Scholar CrossRef Search ADS PubMed  Yang Y., Jiang J., Wang Y., Liu K., Yu Y., Pan J., Ying Y. 2016a. Light-emitting diode spectral sensitivity relationship with growth, feed Intake, meat, and manure characteristics in broilers. T. ASABE  59: 1535– 1539. Yang Y., Yu Y., Yang B., Zhou H., Pan J.. 2016b. Physiological responses to daily light exposure. Sci. Rep . 6: 24808. Google Scholar CrossRef Search ADS   © 2018 Poultry Science Association Inc. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Poultry Science Oxford University Press

The quantitative models for broiler chicken response to monochromatic, combined, and mixed light-emitting diode light: A meta-analysis

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Oxford University Press
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© 2018 Poultry Science Association Inc.
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0032-5791
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1525-3171
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10.3382/ps/pey065
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Abstract

ABSTRACT Although many experiments have been conducted to clarify the response of broiler chickens to light-emitting diode (LED) light, those published results do not provide a solid scientific basis for quantifying the response of broiler chickens. This study used a meta-analysis to establish light spectral models of broiler chickens. The results indicated that 455 to 495 nm blue LED light produced the greatest positive response in body weight by 10.66% (BW; P < 0.001) and 515 to 560 nm green LED light increased BW by 6.27% (P < 0.001) when compared with white light. Regression showed that the wavelength (455 to 660 nm) was negatively related to BW change of birds, with a decrease of about 4.9% BW for each 100 nm increase in wavelength (P = 0.002). Further analysis suggested that a combination of the two beneficial light sources caused a synergistic effect. BW was further increased in birds transferred either from green LED light to blue LED light (17.23%; P < 0.001) or from blue LED light to green LED light (17.52%; P < 0.001). Moreover, birds raised with a mixture of green and blue LED light showed a greater BW promotion (10.66%; P < 0.001) than those raised with green LED light (6.27%). A subgroup analysis indicated that BW response to monochromatic LED light was significant regardless of the genetic strain, sex, control light sources, light intensity and regime of LED light, environmental temperature, and dietary ME and CP (P > 0.05). However, there was an interaction between the FCR response to monochromatic LED light with those covariant factors (P < 0.05). Additionally, green and yellow LED light played a role in affecting the meat color, quality, and nutrition of broiler chickens. The results indicate that the optimal ratio of green × blue of mixed LED light or shift to green-blue of combined LED light may produce the optimized production performance, whereas the optimal ratio of green/yellow of mixed or combined LED light may result in the optimized meat quality. INTRODUCTION Environmental manipulation is an effective means to improve poultry production and welfare (Riber et al., 2018; Rodrigues et al., 2017). Among those environmental factors, light plays a vital role in affecting chicken production. Chickens have highly specialized visual systems (Prescott et al., 2003) and possess five cones (Kram et al., 2010). Colored light prevails in the modern broiler industry, including incandescent (Wells, 1971), fluorescent (Wabeck and Skoglund, 1974), UV (Coleman et al., 1977), commercial colored (Proudfoot and Sefton, 1978), filtered-light lamps (Levenick and Leighton, 1988), and light-emitting diodes (LEDs; Pan et al., 2015; Yang et al., 2016a; Yang et al., 2016b). Among those sources, the LED has a long life, specific wavelength, and adjustable intensity. Such advantages make the LED perfect for supporting poultry growth in a controlled environment. Therefore, many poultry producers have switched from incandescent to LED light devices. Rozenboim et al. (1999) demonstrated that 560 nm and 480 nm LED light stimulates broiler chicken body weight. Yang et al. (2016a) recommended using 580 nm LED light to enhance body weight of broiler chickens. Sadrzadeh et al. (2013) reported that red LED light promoted no increase in body weight and that green LED light suppressed it. However, there are still several gaps concerning monochromatic LED light and broiler chicken growth. Results that have been separately published do not provide scientific basis for quantifying the response of broiler chickens. Meta-analysis is a statistical procedure combining the results of independent studies (Lipsey and Wilson, 2001) and can provide a more precise overall estimate of experimental results. Increasing evidence in agricultural production (Challinor et al., 2014; Pittelkow et al., 2015) and poultry production (Remus et al., 2014; Faridi et al., 2015) has confirmed that meta-analysis is a powerful tool to quantify information. Therefore, the present study was conducted to quantify the effects of monochromatic LED light on the production performance, breast muscle meat quality, and nutrition of broiler chickens. Second, we investigated the interaction between monochromatic LED light and covariant factors, including genetic strain and sex of broiler chickens, light intensity and regime of LED, environmental temperature, and diet composition. Third, based on the results of meta-analysis of monochromatic LED light, we further investigated the effect of the combination and mixture of monochromatic LED light on the performance of broiler chickens. MATERIALS AND METHODS Literature Search Strategy A simple search strategy, implemented in May 2017, was conducted in Scopus (www.scopus.com/; 1998 to 2017), and Web of Science (http://webofknowledge.com/WOS; 1998 to 2017). The algorithm included three broad outcome: Light*OR LED* OR Light-emitting Diodes*, and four broad terms: Chick* OR Chicken*OR Poultry* OR Broiler* OR Gallus*. The light sources were confined to monochromatic LED light, combined LED light which indicated birds were transferred from one monochromatic LED light to another during the growth period, and mixed LED light which was fabricated by two different monochromatic LED lights. Eligibility Criteria and Article Selection The assessment of which publications were eligible for inclusion in the meta-analysis was conducted independently by two evaluators. The selection of which articles which were included or excluded in the present study was based a series of criteria developed by our authors. We used LED lights as treatments and white light as the control group. The LED lights included monochromatic blue LED light (455 to 495 nm; Blue), monochromatic green LED light (515 to 560 nm; Green), monochromatic yellow LED light (585 to 600 nm; Yellow), monochromatic red LED light (615 to 660 nm; Red), Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture). The selected articles contained the wavelength of each LED light source. The experiments were limited to rapidly growing broiler chickens. Also, the selected articles needed sufficient data to determine the “effect size” for production parameters (e.g., the number of birds in each treatment and control group, body weight [BW], and feed conversion ratio [FCR]); a measure of variance (SE or SD) or P-value for each effect estimate. The “effect size” is the weighted difference between treatment and control groups means using the standard deviations and bird numbers of control and treatment groups. We only selected peer-reviewed publications (Halevy et al., 1998; Rozenboim et al., 1999, 2004; Cao et al., 2008, 2012; Karakaya et al., 2009; Ke et al., 2011; Kim et al., 2013a, b; Hassan et al., 2013; Mendes et al., 2013; Sultana et al., 2013; Hassan et al., 2014; Guevara et al., 2015; Seo et al., 2015) which investigated the effects of monochromatic LED, combined, and mixed light on the responses of broiler chickens (n = 7,278 observations; Figure 1). Figure 1. View largeDownload slide The procedure of the meta-analysis performed in the present study, including identification, eligibility, data collection, and statistical analysis. ① Mono-LED light: monochromatic blue, green, yellow, and red LED light; Combined LED light: birds were transferred from one monochromatic LED light to another one during the growth period; mixed LED light: fabricated by two different monochromatic LED light. ② body weight (BW; g), feed conversion ratio (FCR; g/g) BW (g), FCR (g/g), muscle per cent (MP; %), meat quality of pH, cook loss (CL; %), water-holding capacity (WHC; %), shear force (SF; kg/cm2), meat color (L*, a*, and b*), and breast protein content (BPC; %) and breast fat content (BFC; %). ③ Wavelength: the wavelength of LED used in the selected articles; Control: control group; Strain: genetic strain; Sex: sex of broiler chickens; Intensity: light intensity of the LED light; Regime: light regime of the LED light; Temp: environmental temperature during growing period; ME: metabolizable energy of diet; CP: crude protein of diet. Figure 1. View largeDownload slide The procedure of the meta-analysis performed in the present study, including identification, eligibility, data collection, and statistical analysis. ① Mono-LED light: monochromatic blue, green, yellow, and red LED light; Combined LED light: birds were transferred from one monochromatic LED light to another one during the growth period; mixed LED light: fabricated by two different monochromatic LED light. ② body weight (BW; g), feed conversion ratio (FCR; g/g) BW (g), FCR (g/g), muscle per cent (MP; %), meat quality of pH, cook loss (CL; %), water-holding capacity (WHC; %), shear force (SF; kg/cm2), meat color (L*, a*, and b*), and breast protein content (BPC; %) and breast fat content (BFC; %). ③ Wavelength: the wavelength of LED used in the selected articles; Control: control group; Strain: genetic strain; Sex: sex of broiler chickens; Intensity: light intensity of the LED light; Regime: light regime of the LED light; Temp: environmental temperature during growing period; ME: metabolizable energy of diet; CP: crude protein of diet. Data Collection The extracted data included LED wavelength, genetic strain, light source of the control group, light intensity, photoperiod, rearing temperature and dietary composition, number of broiler chickens in control, and treatment groups, BW (g), FCR (g intake/g gain), muscle per cent (MP; %), meat quality of pH, cook loss (CL; %), water-holding capacity (WHC; %), shear force (SF; kg/cm2), meat color (L*, a*, and b*), and breast protein content (BPC; %) and breast fat content (BFC; %), measures of variance of responses (SE or SD), and P-values. In cases where data were presented only in figures, values were extracted using Plot Digitizer (http://plotdigitizer.sourceforge.net/). Statistical Analysis Data extracted from included papers were exported into MS Excel 2013 spreadsheets and formatted for meta-analysis. Many articles reported multiple treatment-control comparisons, which were extracted as unique trials for meta-analysis. Stata was used (version 12; StataCorp, College Station, TX) to analyze performance outcomes by weighted mean difference (WMD), which is also called effect size analysis, in which the difference between treatment and control groups means was weighted using the standard deviations of control and treatment groups (1).   \begin{equation} {\rm{WMD\ }} = \mathop \sum \limits_{i = 1}^m {\rm{\omega }}\left( {{{\rm{X}}_{\rm{t}}} - {{\rm{X}}_{\rm{c}}}} \right), \end{equation} (1)in which Xt and Xc represent means for the treatment group (monochromatic LED light) and the control group (white light), respectively, and ω represents a weighting factor estimated by formula (2):   \begin{equation} \omega {\rm{ }} = {\rm{ }}1/v, \end{equation} (2)where ν is the variance. By giving greater weight (ω) to studies whose estimates have greater precision (lower ν), the precision of the pooled estimate and the statistical power are increased. The variance (ν) is calculated by formula (3):   \begin{equation} {\nu} = \, {^{\rm SD_{\rm t}^{2}}} / {_{\rm n_{\rm t}X_{\rm t}^{2}}}, \end{equation} (3)where SDt and SDc are the SD for the treatment group and the control group, respectively, and nt and nc are the sample sizes for the treatment group and the control group, respectively. If the selected articles reported separate estimates of measure of variance (SE or SD) for each group, these were recorded as such. If the selected literature reported a common SE or SD, the estimate was used for both control and treatment groups. Based on the assumption that significant heterogeneity existed among the experiments, random-effects models were conducted for each performance outcome to estimate the effect size, 95% CI, and statistical significance of WMD. A positive value of WMD indicates that the treatment group provides a greater value than the control group. The pooled effect size was considered significantly if it's associated 95% CI (upper and lower 95% CI) did not overlap with zero and randomization tests yielded P-values <0.05. Meta-regression is applied to test whether evidence exists for different effects in different subgroups of trials using the individual WMD for each experiment as the indicator and the associated SE as the measure of variance. (Knapp and Hartung, 2003). The random effects meta-regression with one covariate and additional between trial variance is given by the following equations, which is the regression of WMD on wavelength with weight ω = 1/v (Thomas and Emery, 1969):   \begin{equation} {\rm{WMD}}\sim{\rm{ N}}\left( {\alpha + \beta \times {\rm{wavelength}},v} \right), \end{equation} (4)where WMD is the performance parameters of broilers, wavelength is the value of trial-specific covariate, v is the variance of effect size within trial, β (slope) represents the change in the performance parameters of broilers per unit of change in the covariate wavelength, and α is intercept (i.e., α = 0; WMD — wavelength), N is the performance parameter of broilers if the covariate i equal to zero. Meta-regression analysis was conducted using LED wavelength as covariate and the BW as the parameter of interest. Data were screened for plausible linear relationships between differences in LED wavelength between the treatment and control group and the BW. The effects of monochromatic, combined, and mixed LED light on performance of broiler chickens are displayed in forest plots, using the estimated WMD of products. Points to the left of the line represent a reduction in the parameter, whereas points to the right of the line indicate an increase in the parameter. Each square represents the mean effect size for that study. The upper and lower limits of the line connected to the square represent the upper and lower 95% CI for the effect size. For ease of interpretation, all WMD were transformed and reported as percentage change in performance parameters for the monochromatic, combined, and mixed LED light group relative to the control group. RESULTS The Effect of Monochromatic LED Light on BW of Broiler Chickens Wavelength When averaged across all studies, the BW was increased by 6.29% (95% CI 5.58 to 6.99; P < 0.001) in broiler chickens stimulated with monochromatic LED light in comparison with those stimulated with white light (Figure 2). Figure 2. View largeDownload slide Body weight (BW), feed conversion ratio (FCR), muscle per cent (MP), meat quality of pH, cook loss (CL), water-holding capacity (WHC), shear force (SF), meat color (L*, a*, and b*), and breast protein content (BPC) and breast fat content (BFC) of broiler chickens reared under various wavelength of monochromatic light-emitting diode light (455 to 495 nm blue, 515 to 560 nm green, 585 to 600 nm yellow, and 615 to 660 nm red) compared with white light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 2. View largeDownload slide Body weight (BW), feed conversion ratio (FCR), muscle per cent (MP), meat quality of pH, cook loss (CL), water-holding capacity (WHC), shear force (SF), meat color (L*, a*, and b*), and breast protein content (BPC) and breast fat content (BFC) of broiler chickens reared under various wavelength of monochromatic light-emitting diode light (455 to 495 nm blue, 515 to 560 nm green, 585 to 600 nm yellow, and 615 to 660 nm red) compared with white light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Further analysis indicated that among various monochromatic LED lights, broiler chickens stimulated with monochromatic 455 to 495 nm blue (Blue), 515 to 560 nm green (Green), and 585 to 600 nm yellow LED light (Yellow) significantly increased BW by 10.66% (95% CI 8.79 to 12.53; P < 0.001), 6.27% (95% CI 4.81 to 7.73; P < 0.001), and 4.18% (95% CI 2.53 to 5.85; P < 0.001), respectively, whereas broiler chickens stimulated with 615 to 660 nm red LED light (Red) showed no significant difference in BW (−0.17%; 95% CI −1.48 to 1.13; P = 0.793; Figure 3). Moreover, meta-regression showed a significant negative linear regression of BW change percentage on 455 to 660 nm wavelength (P = 0.002; Figure 4), with a decrease of about 4.9% BW for each 100 nm increase in wavelength. The regression expression was BW change = −0.0489 × wavelength + 32.808. The critical wavelength was at 600 nm, which suggests that shorter wavelengths (<600 nm) promoted the growth of broiler chickens (BW: 4.18% to 10.66%; R2 = 0.5449; P < 0.001; Figure 3), whereas longer wavelengths (>600 nm) had no impact on the growth of broiler chickens (BW: −0.17%; 95% CI −1.48 to 1.13; P = 0.793; Figure 3). Figure 3. View largeDownload slide Forest plots of body weight (BW) for the subgroup analysis of the effect of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red), light source used in the control group, genetic strain, sex on the BW of broiler chickens. Anak: a local rapid-growing strain in Israel; AA: Arbor Acres; XX: a local rapid-growing strain in Republic of Korea. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 3. View largeDownload slide Forest plots of body weight (BW) for the subgroup analysis of the effect of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red), light source used in the control group, genetic strain, sex on the BW of broiler chickens. Anak: a local rapid-growing strain in Israel; AA: Arbor Acres; XX: a local rapid-growing strain in Republic of Korea. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 4. View largeDownload slide Regression of the wavelength-BW change. The linear regression of BW change of broiler chickens on light wavelength. P < 0.05 indicates that the regression model is significant. Figure 4. View largeDownload slide Regression of the wavelength-BW change. The linear regression of BW change of broiler chickens on light wavelength. P < 0.05 indicates that the regression model is significant. Control Lights Either in contrast with incandescent light, fluorescent light, or white LED light, monochromatic LED light showed a statistically significant effect on BW of broiler chickens (P < 0.05). Among the incandescent light, fluorescent light, and white LED light, the white LED light produced the greatest positive response in BW (8.84%; 95% CI 2.22 to 15.47; P = 0.009), whereas fluorescent light produced the lowest positive response in BW (3.63%; 95% CI 2.77 to 4.49; P < 0.001) compared with monochromatic LED light (Figure 3). Genetic Strain In addition, regardless of the broiler genetic strain, monochromatic LED light had a significant effect on the BW of the broiler chickens (P < 0.05; Figure 3). All strains used in the studies showed a significant difference in BW. The BW of the “Anak”, “Arbor Acres”, “XX”, and “Ross” increased by 3.51% (95% CI 2.21 to 5.11; P < 0.001), 8.84% (95% CI 2.22 to 15.47; P = 0.009), 3.81 (95% CI 3.21 to 4.49; P < 0.001), and 7.89% (95% CI 5.40 to 10.39; P < 0.001), respectively. Sex Monochromatic LED light showed a statistically significant effect on BW of male, female, and mixed sex broiler chickens (P < 0.05; Figure 3). For male broilers, monochromatic LED light increase BW 9.54% (95% CI 5.10 to 13.98; P < 0.001). For female broilers, monochromatic LED light increase BW 2.21% (95% CI 1.82 to 2.608; P < 0.001). For mixed sex broilers, monochromatic LED light increase BW 3.82% (95% CI 1.86 to 5.77; P < 0.001). Environmental Conditions and Diet Nutrition As shown in Figure 5, monochromatic LED light with an intensity of 0.1 W/m2 increased BW by 7.29% (95% CI 5.50 to 9.07; P < 0.001), 10 lux could increase BW by 6.15% (95% CI 3.53 to 8.77; P < 0.001), and 15 lux increase BW by 7.53% (95% CI 4.20 to 10.86; P < 0.001). However, monochromatic LED light with an intensity of 45 lux showed no statistical stimulation of BW of broiler chickens (0.51%; 95% CI −0.02 to 1.05; P = 0.062). For light regime, monochromatic LED light with both continuous lighting (≥23 L) and restricted lighting (≤18 L) promoted BW of broiler chickens by 5.8% (95% CI 4.94 to 6.23; P < 0.001) and 4.94% (95% CI 2.13 to 7.75; P < 0.001), compared with white light. The subgroup analyses of temperature indicated that monochromatic LED light had a significant effect on BW of broiler chickens either at 22 °C or 24°C temperature during the growing-out period (22°C: 7.31% [95% CI 6.04 to 8.57; P < 0.001]; 24°C: 7.80% [95% CI 4.47 to 11.12; P < 0.001]). Figure 5. View largeDownload slide Forest plots of BW for the subgroup analysis of the effect of light intensity, photoperiod, and temperature, diet composition (ME and CP) on the BW of broiler chickens. ≥23 L: 23 h light/1 h dark or 24 h light/0 h dark; ≤18 L: 18 h light/6 h dark or 16 h light/8 h dark. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 5. View largeDownload slide Forest plots of BW for the subgroup analysis of the effect of light intensity, photoperiod, and temperature, diet composition (ME and CP) on the BW of broiler chickens. ≥23 L: 23 h light/1 h dark or 24 h light/0 h dark; ≤18 L: 18 h light/6 h dark or 16 h light/8 h dark. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Monochromatic LED light produced a similar increase in BW of broiler chickens fed with diet of higher ME (>3,100 kcal: 3.80%; 95% CI 1.86 to 5.77; P < 0.001) and normal ME (3,100 kcal: 4.09%; 95% CI 3.14 to 5.04; P < 0.001). However, monochromatic LED light produced a greater increase in BW of broiler chickens fed with diet of higher CP (>175 g/kg: 7.61%; 95% CI 3.10 to 12.11; P < 0.001), whereas a lower increase in BW resulted from diet of normal CP (175 g/kg: 4.09%; 95% CI 3.14 to 5.04; P < 0.001). In addition, the meta-analysis indicated that monochromatic LED light had no effect on MP (1.08%; 95% CI −0.71 to 2.89; P = 0.235; Figure 2), regardless of the wavelength of the LED light. The Effect of Monochromatic LED Light on FCR of Broiler Chickens Wavelength The average FCR of broiler chickens stimulated with monochromatic LED light was significantly decreased by −2.68% (95% CI −3.42 to −1.95; P < 0.001) in comparison with those stimulated with white light (Figure 2). Further analysis indicated that the FCR decrease in broiler chickens varied with the wavelength of the monochromatic LED light. The FCR of broiler chickens stimulated with 455 to 495 nm (Blue) and 585 to 600 nm (Yellow) LED light were significantly decreased by −4.47% (95% CI −5.46 to −3.48; P < 0.001) and −3.06% (95% CI −3.57 to −2.04; P < 0.001), respectively, whereas broiler chickens stimulated with 515 to 560 nm (Green) (−0.49%; 95% CI −1.48 to 0.49; P = 0.314) and 515 to 660 nm (Red) LED light (−2.16%; 95% CI −8.80 to 4.40; P = 0.524) showed no significant difference in FCR (Figure 6). Figure 6. View largeDownload slide Forest plots of FCR for the subgroup analysis of the effect of light-emitting diode (LED) light wavelength (455 to 495 nm blue, 515 to 560 nm green, 585 to 600 nm yellow, and 615 to 660 nm red), light source used in the control group, genetic strain, sex on the FCR of broiler chickens. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 6. View largeDownload slide Forest plots of FCR for the subgroup analysis of the effect of light-emitting diode (LED) light wavelength (455 to 495 nm blue, 515 to 560 nm green, 585 to 600 nm yellow, and 615 to 660 nm red), light source used in the control group, genetic strain, sex on the FCR of broiler chickens. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Control Lights The effect sizes of the FCR response to monochromatic LED light (455 to 660 nm) were dependent on the light source used in the control group. Among the incandescent light, fluorescent light, and white LED light, the white LED light produced a significant negative response in FCR (−11.72%; 95% CI −20.96 to −2.33; P = 0.013), whereas the incandescent light (−0.09%; 95% CI −6.71 to 6.71; P = 0.975) and fluorescent light (−0.77%; 95% CI −1.64 to 0.00; P = 0.066) produced no response in FCR when compared with monochromatic LED light (Figure 6). Genetic Strain In addition, the effect sizes of the FCR response to monochromatic LED light were also dependent on the broiler genetic strain used in the studies. All strains used in the studies showed a significant difference in BW. The BW of the “Anak” and “Arbor Acres” strains could be decreased by −4.10 (95% CI −5.12 to −2.80; P < 0.001) and −11.72% (95% CI −20.96 to −2.33; P = 0.013), respectively, whereas no significant effects were observed for the “XX” (−2.70%; 95% CI −6.96 to 12.61; P = 0.589) and “Ross” (−0.77%; 95% CI −1.64 to 0.00; P = 0.066; Figure 6) strains. Sex The effect sizes of the FCR response to monochromatic LED light were dependent on the sex broiler chickens. For male broilers, monochromatic LED light could decrease FCR by −4.70% (95% CI −5.61 to -3.74; P < 0.001). For female broilers, monochromatic LED light could decrease FCR by −1.75% (95% CI −2.35 to −1.15; P < 0.001). However, for mixed sex broilers, monochromatic LED light showed no effect on the FCR of the broiler chickens (2.70%; 95% CI −7.09 to 12.52; P = 0.589). Environmental Conditions and Diet Nutrition As shown in Figure 7, the subgroup analyses of light. intensity indicated that monochromatic LED light had a similar effect on FCR of broiler chickens exposed to 0.1 W/m2 and 10 lux (0.1 W/m2: −2.34% [95% CI −3.45 to −1.17; P < 0.001]; 10 lux: −1.75% [95% CI −2.35 to −1.15; P < 0.001]). For light regime, continuous lighting (≥23 L) of monochromatic LED light decreased FCR of broiler chickens by −3.98 (95% CI −4.87 to −3.09; P < 0.001). However, restricted lighting (≤18 L) of monochromatic LED light exerted a little effect on FCR (−0.38%; 95% CI −1.13 to 0.32; P = 0.295). Monochromatic LED light could decrease FCR of 24°C-treated broilers by −0.71% (95% CI −2.54 to −0.88; P < 0.001), whereas monochromatic LED light had no influence on FCR of 22°C-treated broilers (0.32%; 95% CI −7.17 to 7.85; P = 0.933). As shown in Figure 5, the effect of monochromatic LED light on FCR had no statistical correlation with ME and CP of diet. Figure 7. View largeDownload slide Forest plots of FCR for the subgroup analysis of the effect of light intensity, photoperiod, temperature, diet composition (ME and CP) on the FCR of broiler chickens. The number of observations in each category is displayed in parentheses. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 7. View largeDownload slide Forest plots of FCR for the subgroup analysis of the effect of light intensity, photoperiod, temperature, diet composition (ME and CP) on the FCR of broiler chickens. The number of observations in each category is displayed in parentheses. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. The Effect of Monochromatic LED Light on Breast Muscle Meat Characteristics of Broiler Chickens Breast Muscle Meat Color Monochromatic LED light exhibited no effect on the L* value of breast meat (1.02%; 95% CI −0.61 to 2.67; P = 0.22; Figure 2): not 455 to 495 nm (Blue) LED light (−2.33%; 95% CI −11.41 to 6.76; P = 0.617), 515 to 560 nm (Green) LED light (1.00%; 95% CI −5.36 to 7.36; P = 0.758), 585 to 600 nm (Yellow) LED light (4.22%; 95% CI −4.41 to 12.86; P = 0.495), or 615 to 660 nm (Red) LED light (2.95%; 95% CI −5.51 to 11.39; P = 0.495; Table 1). The same situation was also observed for the a* value (1.81%; 95% CI −1.03 to 4.25; P = 0.976; Table 1) and the L* value of breast meat. However, although they did not produce the same overall effects of the monochromatic LED light, yellow and red LED lights significantly increased the b* value of the breast meat (Yellow: −3.69%; 95% CI 0.65 to 6.62; P = 0.016; Red: 2.26%; 95% CI 0.75 to 3.77; P = 0.003) (Table 1). Table 1. The effects of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red) on meat quality of pH, cook loss (CL), water-holding capacity (WHC), shear force (SF), meat color (L*, a*, and b*), and breast protein content (BPC) and breast fat content (BFC) compared with white light. Data are expressed as means ± 95% confidence interval (CI).1 Variable  pH  CL  WHC  SF  L*  a*  b*  BPC  BFC  Blue  Mean  1.86  −14.22*  −5.23*  −10.70*  −2.33  4.51  −11.43  0.043  0.00    LCI  −1.01  −25.43  −9.19  −18.42  −11.41  −6.12  −26.52  −3.61  −35.90    UCI  4.56  −2.99  −1.34  −2.97  6.76  7.92  3.48  3.65  35.90    P-value  0.216  0.013  0.009  0.007  0.617  0.978  0.132  0.988  0.998  Green  Mean  1.69*  −9.90*  −7.83*  13.96*  1.00  −12.45  5.49  0.087  5.90    LCI  1.02  −14.58  −11.50  2.91  −5.36  −26. 94  −14.97  −5.17  −30.41    UCI  2.20  −5.15  −4.28  25.02  7.36  24.11  26.11  5.34  41.76    P-value  <0.001  <0.001  <0.001  0.014  0.758  0.923  0.597  0.974  0.754  Yellow  Mean  0.17  −3.50  −6.32*  −10.99  4.22  26.95  3.69*  −1.95*  34.13*    LCI  −1.69  −9.55  −10.99  −27.74  −4.41  −68.93  0.65  −3.83  11.38    UCI  1.86  2.55  −1.37  6.04  12.86  72.12  6.62  −0.09  57.48    P-value  0.924  0.648  0.011  0.205  0.495  0.941  0.016  0.039  0.003  Red  Mean  −1.98*  1.45  −8.04  6.73*  2.95  44.44  2.26*  −2.08*  30.61    LCI  −3.63  −4.79  −20.30  0.28  −5.51  −81.66  0.75  −2.87  −36.56    UCI  −0.49  7.76  4.42  13.18  11.38  90.56  3.77  −1.35  97.79    P-value  0.014  0.255  0.205  0.042  0.338  0.919  0.003  <0.001  0.373  Variable  pH  CL  WHC  SF  L*  a*  b*  BPC  BFC  Blue  Mean  1.86  −14.22*  −5.23*  −10.70*  −2.33  4.51  −11.43  0.043  0.00    LCI  −1.01  −25.43  −9.19  −18.42  −11.41  −6.12  −26.52  −3.61  −35.90    UCI  4.56  −2.99  −1.34  −2.97  6.76  7.92  3.48  3.65  35.90    P-value  0.216  0.013  0.009  0.007  0.617  0.978  0.132  0.988  0.998  Green  Mean  1.69*  −9.90*  −7.83*  13.96*  1.00  −12.45  5.49  0.087  5.90    LCI  1.02  −14.58  −11.50  2.91  −5.36  −26. 94  −14.97  −5.17  −30.41    UCI  2.20  −5.15  −4.28  25.02  7.36  24.11  26.11  5.34  41.76    P-value  <0.001  <0.001  <0.001  0.014  0.758  0.923  0.597  0.974  0.754  Yellow  Mean  0.17  −3.50  −6.32*  −10.99  4.22  26.95  3.69*  −1.95*  34.13*    LCI  −1.69  −9.55  −10.99  −27.74  −4.41  −68.93  0.65  −3.83  11.38    UCI  1.86  2.55  −1.37  6.04  12.86  72.12  6.62  −0.09  57.48    P-value  0.924  0.648  0.011  0.205  0.495  0.941  0.016  0.039  0.003  Red  Mean  −1.98*  1.45  −8.04  6.73*  2.95  44.44  2.26*  −2.08*  30.61    LCI  −3.63  −4.79  −20.30  0.28  −5.51  −81.66  0.75  −2.87  −36.56    UCI  −0.49  7.76  4.42  13.18  11.38  90.56  3.77  −1.35  97.79    P-value  0.014  0.255  0.205  0.042  0.338  0.919  0.003  <0.001  0.373  1SE = (UCI − LCI)/2Z, in which the Z score is equal to 1.96, when α = 0.05. Effect sizes were considered significant if the 95% CI (upper 95% CI [UCI] and lower 95% CI [LCI]) did not overlap with 0. *P < 0.05. View Large Table 1. The effects of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red) on meat quality of pH, cook loss (CL), water-holding capacity (WHC), shear force (SF), meat color (L*, a*, and b*), and breast protein content (BPC) and breast fat content (BFC) compared with white light. Data are expressed as means ± 95% confidence interval (CI).1 Variable  pH  CL  WHC  SF  L*  a*  b*  BPC  BFC  Blue  Mean  1.86  −14.22*  −5.23*  −10.70*  −2.33  4.51  −11.43  0.043  0.00    LCI  −1.01  −25.43  −9.19  −18.42  −11.41  −6.12  −26.52  −3.61  −35.90    UCI  4.56  −2.99  −1.34  −2.97  6.76  7.92  3.48  3.65  35.90    P-value  0.216  0.013  0.009  0.007  0.617  0.978  0.132  0.988  0.998  Green  Mean  1.69*  −9.90*  −7.83*  13.96*  1.00  −12.45  5.49  0.087  5.90    LCI  1.02  −14.58  −11.50  2.91  −5.36  −26. 94  −14.97  −5.17  −30.41    UCI  2.20  −5.15  −4.28  25.02  7.36  24.11  26.11  5.34  41.76    P-value  <0.001  <0.001  <0.001  0.014  0.758  0.923  0.597  0.974  0.754  Yellow  Mean  0.17  −3.50  −6.32*  −10.99  4.22  26.95  3.69*  −1.95*  34.13*    LCI  −1.69  −9.55  −10.99  −27.74  −4.41  −68.93  0.65  −3.83  11.38    UCI  1.86  2.55  −1.37  6.04  12.86  72.12  6.62  −0.09  57.48    P-value  0.924  0.648  0.011  0.205  0.495  0.941  0.016  0.039  0.003  Red  Mean  −1.98*  1.45  −8.04  6.73*  2.95  44.44  2.26*  −2.08*  30.61    LCI  −3.63  −4.79  −20.30  0.28  −5.51  −81.66  0.75  −2.87  −36.56    UCI  −0.49  7.76  4.42  13.18  11.38  90.56  3.77  −1.35  97.79    P-value  0.014  0.255  0.205  0.042  0.338  0.919  0.003  <0.001  0.373  Variable  pH  CL  WHC  SF  L*  a*  b*  BPC  BFC  Blue  Mean  1.86  −14.22*  −5.23*  −10.70*  −2.33  4.51  −11.43  0.043  0.00    LCI  −1.01  −25.43  −9.19  −18.42  −11.41  −6.12  −26.52  −3.61  −35.90    UCI  4.56  −2.99  −1.34  −2.97  6.76  7.92  3.48  3.65  35.90    P-value  0.216  0.013  0.009  0.007  0.617  0.978  0.132  0.988  0.998  Green  Mean  1.69*  −9.90*  −7.83*  13.96*  1.00  −12.45  5.49  0.087  5.90    LCI  1.02  −14.58  −11.50  2.91  −5.36  −26. 94  −14.97  −5.17  −30.41    UCI  2.20  −5.15  −4.28  25.02  7.36  24.11  26.11  5.34  41.76    P-value  <0.001  <0.001  <0.001  0.014  0.758  0.923  0.597  0.974  0.754  Yellow  Mean  0.17  −3.50  −6.32*  −10.99  4.22  26.95  3.69*  −1.95*  34.13*    LCI  −1.69  −9.55  −10.99  −27.74  −4.41  −68.93  0.65  −3.83  11.38    UCI  1.86  2.55  −1.37  6.04  12.86  72.12  6.62  −0.09  57.48    P-value  0.924  0.648  0.011  0.205  0.495  0.941  0.016  0.039  0.003  Red  Mean  −1.98*  1.45  −8.04  6.73*  2.95  44.44  2.26*  −2.08*  30.61    LCI  −3.63  −4.79  −20.30  0.28  −5.51  −81.66  0.75  −2.87  −36.56    UCI  −0.49  7.76  4.42  13.18  11.38  90.56  3.77  −1.35  97.79    P-value  0.014  0.255  0.205  0.042  0.338  0.919  0.003  <0.001  0.373  1SE = (UCI − LCI)/2Z, in which the Z score is equal to 1.96, when α = 0.05. Effect sizes were considered significant if the 95% CI (upper 95% CI [UCI] and lower 95% CI [LCI]) did not overlap with 0. *P < 0.05. View Large Breast Muscle Meat Quality For pH value and SF, no significant effects were observed in broiler chickens stimulated with the monochromatic LED light in contrast with those stimulated with white light (pH: 0.84% [95% CI −0.34 to 1.87; P = 0.139]; SF: −0.34% [95% CI −3.75 to 3.24; P = 0.89]; Figure 2). However, significant effects were found in CL and WHC in broiler chickens stimulated with the monochromatic LED light in contrast with those stimulated with white light (CL: −7.73% [95% CI −11.25 to −4.21; P < 0.001]; WHC: −6.64% [95% CI −8.93 to −4.35; P < 0.001]; Figure 2). Further meta-analysis indicated that 455 to 495 nm (Blue) LED light significantly decreased the CL (−14.22%; 95% CI −25.43 to −2.99; P = 0.013), WHC (−5.23%; 95% CI −9.19 to −1.34; P = 0.009), and SF (−10.70%; 95% CI −18.42 to −2.97; P = 0.007) in breast meat compared with white light (Table 1). Further, 515 to 560 nm (Green) LED light significantly decreased the CL (−9.90%; 95% CI −14.58 to −5.15; P < 0.001) and WHC (−7.83%; 95% CI −11.50 to −4.28; P < 0.001), whereas it increased the pH value (1.69%; 95% CI 1.02 to 2.20; P < 0.001) and SF (13.96%; 95% CI 2.91 to 25.02; P = 0.014) in breast meat compared with white light. The 585 to 600 nm (Yellow) LED light had a negative effect on WHC (−6.32%; 95% CI −10.99 to −1.37; P = 0.011), whereas 615 to 660 nm (Red) LED light had a positive effect on SF (6.73%; 95% CI 0.28 to 13.18; P = 0.042) in breast meat compared with white light. Breast Muscle Meat Nutrition No significant difference was observed in BPC of broiler chickens stimulated with monochromatic LED light (−0.87%; 95% CI −2.74 to 1.00; P = 0.357; Figure 2), in contrast with white light. However, 585 to 600 nm (Yellow) (−1.95%; 95% CI −3.83 to −0.09; P = 0.039) and 615 to 660 nm (Red) LED light (−2.08%; 95% CI −2.87 to −1.35; P < 0.001) caused a negative response to BPC (Table 1). For BFC, monochromatic LED light had an overall effect on BFC (10.47%; 95% CI 0.46 to 20.48; P = 0.043; Figure 2). Moreover, 585 to 600 nm (Yellow) LED light produced the greatest positive response in BFC (34.13%; 95% CI 11.38 to 57.48; P = 0.003). The Effect of Combined and Mixed LED Light on Performance of Broiler Chickens The effect of combined and mixed LED light on BW of broiler chickens are shown in Figure 8. When averaged across all studies, BW was further increased in broiler chickens stimulated with Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture) in comparison with those stimulated with white light (G-B combination: 17.23% [95% CI 16.89 to 17.58; P < 0.001]; B-G combination: 17.52% [95% CI 17.06 to 17.97; P < 0.001]; G × B mixture: 10.66% [95% CI 7.29 to 14.02; P < 0.001]). Figure 8. View largeDownload slide Body weight (BW) of broiler chickens reared under 455 to 495 nm blue LED light (Blue), 515 to 560 nm green LED light (Green), Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture) compared with white light. G-B combination, birds from monochromatic green LED light were transferred to monochromatic blue LED light. B-G combination, birds from monochromatic blue LED light were transferred to monochromatic green LED light. G × B mixture, birds were exposed to Green × Blue mixed LED light, which was fabricated by monochromatic green and blue LED light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 8. View largeDownload slide Body weight (BW) of broiler chickens reared under 455 to 495 nm blue LED light (Blue), 515 to 560 nm green LED light (Green), Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture) compared with white light. G-B combination, birds from monochromatic green LED light were transferred to monochromatic blue LED light. B-G combination, birds from monochromatic blue LED light were transferred to monochromatic green LED light. G × B mixture, birds were exposed to Green × Blue mixed LED light, which was fabricated by monochromatic green and blue LED light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. The average FCR of broiler chickens stimulated with Green-Blue combined LED light, Blue-Green combined LED light, and Green × Blue mixed LED light was further decreased in comparison with those stimulated with white light (G-B combination: −9.61% [95% CI −12.94 to −6.28; P < 0.001]; B-G combination: −11.70% [95% CI −15.40 to −7.99; P < 0.001]; G × B mixture: −4.00% [95% CI −5.14 to −2.86; P < 0.001]; Figure 9). Figure 9. View largeDownload slide Feed conversion ratio (FCR) of broiler chickens reared under 455 to 495 nm blue LED light (Blue), 515 to 560 nm green LED light (Green), Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture) compared with white light. G-B combination, birds from monochromatic green LED light were transferred to monochromatic blue LED light. B-G combination, birds from monochromatic blue LED light were transferred to monochromatic green LED light. G × B mixture, birds were exposed to Green × Blue mixed LED light, which was fabricated by monochromatic green and blue LED light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. Figure 9. View largeDownload slide Feed conversion ratio (FCR) of broiler chickens reared under 455 to 495 nm blue LED light (Blue), 515 to 560 nm green LED light (Green), Green-Blue combined LED light (G-B combination), Blue-Green combined LED light (B-G combination), and Green × Blue mixed LED light (G × B mixture) compared with white light. G-B combination, birds from monochromatic green LED light were transferred to monochromatic blue LED light. B-G combination, birds from monochromatic blue LED light were transferred to monochromatic green LED light. G × B mixture, birds were exposed to Green × Blue mixed LED light, which was fabricated by monochromatic green and blue LED light. Data are expressed as means ± 95% confidence interval (CI). *P < 0.05. DISCUSSION Due to the potential advantages of LEDs, multiple studies have been conducted to investigate the potential application of LED light in poultry husbandry. However, the quantification of the relationships between LED light and the response of broiler chickens still have not been identified. While there have been attempts to summarize the relationships between LED light and the response of broiler chickens (Halevy et al., 2006; Parvin et al., 2014a,b), those studies were conducted under different conditions and the results are sometimes contradictory and inconclusive. Therefore, it is hard to draw general conclusions from the results. This study used a meta-analysis to model the response of the broiler chickens to monochromatic LED light. Further to quantify the effect of the combination and mixture of monochromatic LED light on the response of the broiler chickens. Final, we investigated the interactions between monochromatic LED light and covariant factors. We hypothesize that a light spectrum with shorter wavelengths results in beneficial growth whereas that with longer wavelengths has a negative effect on growth. Our meta-analysis confirmed this hypothesis and supports previous reports by Olanrewaju et al. (2015) and Huth and Archer (2015). Olanrewaju et al. (2015) evaluated the effects of color temperatures of LED lamps on growth performance of broiler chickens and showed that the BW gains of broiler chickens stimulated with incandescent light (2,010 K) were statistically similar to those of broiler chickens stimulated with warm LED light (2,700 K), but were statistically lower than those of broiler chickens stimulated with cool LED light (5,000 K). This is possibly caused by the difference in spectrum between warm and cool LEDs. Warm cool LEDs both have two large gradual peaks, but they are not the same. Warm LED has a major peak at 630 nm (red light) and a minor peak at 460 nm (blue light). A cool LED has a major peak at 460 nm (blue light) and a minor peak at 520 to 590 nm (green to yellow light; Olanrewaju et al., 2015). Based on the negative relationship between light wavelength and BW change of broiler chickens found in the present study, it is conceivable that the growth promotion in broiler chickens was attributable to an increase in the blue portion of the spectrum in the cool LED. The above analysis suggests that it is possible to optimize broiler chicken growth by giving an optimal ratio of blue/green light. To confirm this hypothesis, the present study found that BW was further increased in broiler chickens transferred either from green LED light to blue LED light (G-B combination: 17.23%; P < 0.001) or from blue LED light to green LED light (B-G combination: 17.52%; P < 0.001). Broiler chickens exposed to the mixture of green and blue LED light showed a greater BW promotion (G × B mixture: 10.66%; P < 0.001) than those exposed to green LED light (Green: 6.27%). The present study found that FCR was significantly improved by 455 to 495 nm (Blue) LED light (−4.47%; P < 0.001), whereas no effect was observed for 515 to 560 nm (Green) LED light (−0.49%; P = 0.314) compared with white light. Moreover, further analysis indicated that FCR was further improved in broiler chickens transferred either from green LED light to blue LED light (G-B combination: −9.61%; P < 0.001) or from blue LED light to green LED light (B-G combination: −11.70%; P < 0.001). Broiler chickens exposed to a mixture of green and blue LED light showed a similar FCR promotion (G × B mixture: −4.00%; P < 0.001) with those exposed to blue LED light (Blue: −4.47%). Previous behavior tests suggested that red- or white light-treated broiler chickens expressed more aggressive activity (Prayitno et al., 1997) and that blue light-treated broiler chickens were calmer than those treated by white light (Rodenboog, 2001). The blue light also has been found to decrease cortisol concentrations in serum compared to white light, suggesting blue light alleviates the stress response in broiler chickens (Xie et al., 2008). The decreased stress in broiler chickens (Abdo et al., 2017) caused by blue light might use less energy in response to stressors, which decreased the “waste energy” and might increase the amount of energy for growth stimulation. Taken together, the results of the behavior and stress tests might explain the better FCR in broiler chickens stimulated with blue light. This meta-analysis based on published data quantitatively identified the response of the broiler chickens to monochromatic, combined, and mixed LED light. Subgroup analysis indicated that BW responses to monochromatic LED light were statistically significant regardless of the genetic strain and sex of broiler chickens, control light sources, light intensity and regime of LED light, environmental temperature, and dietary ME and CP. However, FCR responses to monochromatic LED light interacted with the genetic strain and sex of broiler chickens, control light sources, light intensity and regime of LED light, environmental temperature, and dietary ME and CP. Monochromatic blue LED light promoted better performance of the main production performance (BW and FCR) of broiler chickens compared with white light. The combination and mixture of the monochromatic blue and green LED light could further improve the production performance of broiler chickens. Monochromatic green and yellow LED light played a role in affecting the meat color quality and nutrition of broiler chickens (Table 2). The further study should be designed to optimize broiler production by the optimal ratio of green × blue of mixed LED light or a shift to green-blue combined LED light, whereas optimize the meat quality and nutrition by the optimal ratio of green/yellow of mixed or combined LED light. Table 2. The summary of the effect of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red) on performance of broiler chickens.     View Large Table 2. The summary of the effect of 455 to 495 nm blue LED (Blue), 515 to 560 nm green LED (Green), 585 to 600 nm yellow LED (Yellow), 615 to 660 nm red LED light (Red) on performance of broiler chickens.     View Large Footnotes 1 This work was supported by the National Key Research and Development Program of China (NO. 2017YFB0404000). REFERENCES Abdo S. E., Elkassas S., Elnahas A. F., Mahmoud S. 2017. Modulatory effect of monochromatic blue light on heat stress response in commercial broilers. Sci Rep . 4: 1361– 1370. Cao J., Liu W., Wang Z., Xie D., Jia L., Chen Y.. 2008. Green and blue monochromatic lights promote growth and development of broilers via stimulating testosterone secretion and myofiber growth. The Journal of Applied Poultry Research . 17: 211– 218. Google Scholar CrossRef Search ADS   Cao J., Wang Z., Dong Y., Zhang Z., Li J., Li F., Chen Y.. 2012. Effect of combinations of monochromatic lights on growth and productive performance of broilers. Poultry Science . 91: 3013– 3018. Google Scholar CrossRef Search ADS PubMed  Challinor A. J., Watson J., Lobell D. B., Howden S. M., Smith D. R., Chhetri N.. 2014. A meta-analysis of crop yield under climate change and adaptation. Nature Clim Change  4: 287– 291. Google Scholar CrossRef Search ADS   Coleman M., McDaniel G., Neeley W., Ivey W.. 1977. Physical comparisons of lighted incubation in avian eggs. Poultry Science . 56: 1421– 1425. Google Scholar CrossRef Search ADS   Faridi A., Gitoee A., France J.. 2015. A meta-analysis of the effects of nonphytate phosphorus on broiler performance and tibia ash concentration. Poultry Science . 94: 2753– 2762. Google Scholar CrossRef Search ADS PubMed  Guevara B., Pech P., Zamora B., Navarrete S., Magaña S. 2015. Performance of broilers reared under monochromatic light emitting diode supplemental lighting. Rev. Bras. Cienc. Avic. . 17: 553– 558. Google Scholar CrossRef Search ADS   Halevy O., Biran I., Rozenboim I.. 1998. Various light source treatments affect body and skeletal muscle growth by affecting skeletal muscle satellite cell proliferation in broilers. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology  120: 317– 323. Google Scholar CrossRef Search ADS   Halevy O., Yahav S., Rozenboim I.. 2006. Enhancement of meat production by environmental manipulations in embryo and young broilers. World's Poult. Sci. J . 62: 485– 497. Hassan R., Sultana S., Choe H. S. 2013. A comparison of monochromatic and mixed led light color on performance, bone mineral density, meat and blood properties, and immunity of broiler chicks. J. Poult. Sci . 51: 195– 201. Hassan M. R., Sultana S., Choe H. S., Ryu K. S.. 2014. A comparison of monochromatic and mixed LED light color on performance, bone mineral density, meat and blood properties, and immunity of broiler chicks. J. Poult. Sci . 51: 195– 201. Google Scholar CrossRef Search ADS   Huth J. C., Archer G. S.. 2015. Comparison of two LED light bulbs to a dimmable CFL and their effects on broiler chicken growth, stress, and fear. Poultry Science . 94: 2027– 2036. Google Scholar CrossRef Search ADS PubMed  Karakaya M., Parlat S., Yilmaz M., Yildirim I., Ozalp B.. 2009. Growth performance and quality properties of meat from broiler chickens reared under different monochromatic light sources. British Poultry Science . 50: 76– 82. Google Scholar CrossRef Search ADS PubMed  Ke Y., Liu W., Wang Z., Chen Y.. 2011. Effects of monochromatic light on quality properties and antioxidation of meat in broilers. Poultry Science . 90: 2632– 2637. Google Scholar CrossRef Search ADS PubMed  Kim M. J., Parvin R., Mushtaq M. M. H., Hwangbo J., Kim J. H., Na J. C., Kim D. W., Kang H. K., Kim C. D., Cho K. O., Yang C. B., Choi H. C.. 2013. Growth performance and hematological traits of broiler chickens reared under assorted monochromatic light sources. Poultry Science . 92: 1461– 1466. Google Scholar CrossRef Search ADS PubMed  Knapp G., Hartung J.. 2003. Improved tests for a random effects meta-regression with a single covariate. Statist. Med.  22: 2693– 2710. Google Scholar CrossRef Search ADS   Kram Y. A., Mantey S., Corbo J. C.. 2010. Avian cone photoreceptors tile the retina as five independent, self-organizing mosaics. Plos One  5: e8992. Google Scholar CrossRef Search ADS PubMed  Levenick C., Leighton A.. 1988. Effects of Photoperiod and Filtered Light on Growth, Reproduction, and Mating Behavior of Turkeys.: 1. Growth Performance of Two Lines of Males and Females. Poultry Science . 67: 1505– 1513. Google Scholar CrossRef Search ADS PubMed  Lipsey M. W., Wilson D. B.. 2001. Practical meta-analysis . Sage Publications, Inc. Mendes A. S., Paixão S. J., Restelatto R., Morello G. M., de Moura D. J., Possenti J. C.. 2013. Performance and preference of broiler chickens exposed to different lighting sources. The Journal of Applied Poultry Research . 22: 62– 70. Google Scholar CrossRef Search ADS   Olanrewaju H., Purswell J., Maslin W., Collier S., Branton S.. 2015. Effects of color temperatures (kelvin) of LED bulbs on growth performance, carcass characteristics, and ocular development indices of broilers grown to heavy weights. Poultry Science . 94: 338– 344. Google Scholar CrossRef Search ADS PubMed  Pan J., Yang Y., Yang B., Dai W., Yu Y.. 2015. Human-friendly light-emitting diode source stimulates broiler growth. Plos One . 10: e0135330. Google Scholar CrossRef Search ADS PubMed  Parvin R., Mushtaq M., Kim M., Choi H.. 2014a. Light emitting diode (LED) as a source of monochromatic light: A novel lighting approach for behaviour, physiology and welfare of poultry. Worlds Poultry Science Journal . 70: 543– 556. Google Scholar CrossRef Search ADS   Parvin R., Mushtaq M., Kim M., Choi H.. 2014b. Light emitting diode (LED) as a source of monochromatic light: A novel lighting approach for immunity and meat quality of poultry. Worlds Poultry Science Journal . 70: 557– 562. Google Scholar CrossRef Search ADS   Pittelkow C. M., Liang X., Linquist B. A., van Groenigen K. J., Lee J., Lundy M. E., van Gestel N., Six J., Venterea R. T., van Kessel C.. 2015. Productivity limits and potentials of the principles of conservation agriculture. Nature  517: 365– 368. Google Scholar CrossRef Search ADS PubMed  Prayitno D., Phillips C., Omed H.. 1997. The effects of color of lighting on the behavior and production of meat chickens. Poultry Science . 76: 452– 457. Google Scholar CrossRef Search ADS PubMed  Prescott N., Wathes C. M., Jarvis J.. 2003. Light, vision and the welfare of poultry. Animal Welfare  12: 269– 288. Proudfoot F., Sefton A.. 1978. Feed texture and light treatment effects on the performance of chicken broilers. Poultry Science . 57: 408– 416. Google Scholar CrossRef Search ADS   Remus A., Hauschild L., Andretta I., Kipper M., Lehnen C. R., Sakomura N. K.. 2014. A meta-analysis of the feed intake and growth performance of broiler chickens challenged by bacteria. Poult. Sci . 93: 1149– 1158. Google Scholar CrossRef Search ADS PubMed  Riber A. B., Ha V. D. W., de Jong I. C., Steenfeldt S. 2018. Review of environmental enrichment for broiler chickens. Poult. Sci . 97: 378– 396. Google Scholar CrossRef Search ADS PubMed  Rodenboog H. 2001. Sodium, green, blue, cool or warm-white light. World Poult . 17: 22– 23. Rodrigues I., Svihus B., Bedford M. R., Gous R., Choct M. 2017. Intermittent lighting improves resilience of broilers during the peak phase of sub-clinical necrotic enteritis infection. Poult. Sci . 97: 438– 446. Google Scholar CrossRef Search ADS   Rozenboim I., Biran I., Chaiseha Y., Yahav S., Rosenstrauch A., Sklan D., Halevy O.. 2004. The effect of a green and blue monochromatic light combination on broiler growth and development. Poultry Science . 83: 842– 845. Google Scholar CrossRef Search ADS PubMed  Rozenboim I., Biran I., Uni Z., Robinzon B., Halevy O.. 1999. The effect of monochromatic light on broiler growth and development. Poultry Science . 78: 135– 138. Google Scholar CrossRef Search ADS PubMed  Sadrzadeh A., Brujeni G. N., Livi M., Nazari M. J., Sharif M. T., Hassanpour H., Haghighi N.. 2013. Cellular immune response of infectious bursal disease and Newcastle disease vaccinations in broilers exposed to monochromatic lights. Afr. J. Biotechnol . 10: 9528– 9532. Seo H.-S., Kang M., Yoon R.-H., Roh J.-H., Wei B., Ryu K. S., Cha S.-Y., Jang H.-K.. 2015. Effects of various LED light colors on growth and immune response in broilers. Jpn. Poult. Sci. . 53: 76– 81. Google Scholar CrossRef Search ADS   Sultana S., Hassan M., Choe H. S., Ryu K. S.. 2013. The effect of monochromatic and mixed LED light colour on the behaviour and fear responses of broiler chicken. Avian Biol Res . 6: 207– 214. Google Scholar CrossRef Search ADS   Thomas J. W., Emery R. S.. 1969. Additive nature of sodium bicarbonate and magnesium oxide on milk fat concentrations of milking cows fed restricted-roughage rations. Journal of Dairy Science . 52: 1762– 1769. Google Scholar CrossRef Search ADS   Wabeck C., Skoglund W.. 1974. Influence of Radiant Energy from Fluorescent Light Sources on Growth, Mortality, and Feed Conversion of Broilers. Poultry Science . 53: 2055– 2059. Google Scholar CrossRef Search ADS PubMed  Wells R. 1971. A comparison of red and white light and high and low dietary protein regimes for growing pullets. British Poultry Science . 12: 313– 325. Google Scholar CrossRef Search ADS PubMed  Xie D., Wang Z. X., Dong Y. L., Cao J., Wang J. F., Chen J. L., Chen Y. X.. 2008. Effects of monochromatic light on immune response of broilers. Poultry Science . 87: 1535– 1539. Google Scholar CrossRef Search ADS PubMed  Yang Y., Jiang J., Wang Y., Liu K., Yu Y., Pan J., Ying Y. 2016a. Light-emitting diode spectral sensitivity relationship with growth, feed Intake, meat, and manure characteristics in broilers. T. ASABE  59: 1535– 1539. Yang Y., Yu Y., Yang B., Zhou H., Pan J.. 2016b. Physiological responses to daily light exposure. Sci. Rep . 6: 24808. Google Scholar CrossRef Search ADS   © 2018 Poultry Science Association Inc. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

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Poultry ScienceOxford University Press

Published: Mar 27, 2018

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