Research Notes Effect of monochromatic light stimuli during embryogenesis on muscular growth, chemical composition, and meat quality of breast muscle in male broilers L. Zhang,* H. J. Zhang, X. Qiao, 1 H. Y. Yue, S. G. Wu, J. H. Yao,* 2 and G. H. Qi 2 * College of Animal Science and Technology, Northwest A & F University, Yangling, Shaanxi 712100, China; and Key Laboratory of Feed Biotechnology of Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, China ABSTRACT This study was conducted to evaluate the effect of monochromatic light stimuli during embryogenesis on breast muscle growth, chemical composition, and meat quality of male broilers. Fertile broiler eggs (Arbor Acres; n = 1,320) were preweighed and randomly assigned to 1 of 3 treatment groups in 3 modified incubators: 1) control group (in dark condition), 2) monochromatic green light group (560 nm), and 3) monochromatic blue light group (480 nm). The monochromatic lighting systems sourced from light-emitting diode lamps and were equalized at the intensity of 15 lx at eggshell level. After hatch, 120 male chicks from each group were placed in 6 replicates with 20 birds each. All of the birds were housed under white light (30 lx at bird-head level) with a light schedule of 23L:1D. At 21, 35, and 42 d of age, BW and breast muscle weight in the green light group were significantly increased compared with birds in the blue or dark groups (P < 0.05). The breast muscle weight and breast muscle percentages in birds incubated under green light were significantly elevated by 50.39 g (0.76%) and 54.07 g (1.20%) than those in the dark condition or blue group at 42 d of market age (P < 0.05), respectively. In the green light group, feed intake during 0~42 d was higher than that in the other 2 treatment groups (P < 0.05); feed conversion ratio during 0~35 and 0~42 d were lower than that in the dark condition (P < 0.05). No significant differences in the contents of breast moisture, CP, crude fat, and crude ash among all groups were observed (P > 0.05). Green light stimuli tended to increase cooking loss (P = 0.08) and L* value of 24-h meat color (P = 0.09). These results suggest that green light stimuli during embryogenesis enhanced the posthatch BW of male broilers, increased breast muscle growth, and improved the feed conversion ratio, but it did not cause any noticeable changes in breast chemical composition or overall meat quality characteristics. Key words: broiler embryo, monochromatic light, breast muscle, chemical composition, meat quality 2012 Poultry Science 91 :1026 1031 http://dx.doi.org/10.3382/ps.2011-01899 INTRODUCTION In modern poultry industry, artificial illumination has been widely used to promote avian productive performance. Thus, the source, spectra, and intensity of light supplementation have become important environmental factors in modern broiler management. Many previous studies have focused on the effect of light spectra on the growth performance in broilers. Broilers reared under green or blue light showed significantly more BW gain and greater muscle growth 2012 Poultry Science Association Inc. Received September 27, 2011. Accepted December 31, 2011. 1 A visiting graduate student from College of Animal Science of South China Agricultural University. 2 Corresponding authors: yaojunhu2004@sohu.com or qiguanghai@ mail.caas.net.cn than birds reared under red or white light (Wabeck and Skuglund, 1974; Rozenboim et al., 1999; Cao et al., 2008), whereas feed conversion and mortality were not affected (Wabeck and Skuglund, 1974). Green light accelerates broiler muscle growth during the early stage, whereas blue light stimulates growth in the later stage (Rozenboim et al., 1999, 2004a; Cao et al., 2008). The influence of light stimuli on avian embryos was also investigated several decades ago. Early studies reported that stimulation with white light during incubation increased embryo weight in White Rock chickens (Siegel et al., 1969), broilers (Walter and Voitle, 1972, 1973), turkeys (Cooper, 1972), White Leghorn chickens (Coleman and McDaniel, 1975), and quails (Walter and Voitle, 1973). However, Lauber (1975) observed that the White Leghorn eggs stimulated with green light (566 ± 15 nm) showed a significantly higher embryo weight, as did blue-violet light (400 nm). Light affects avian em- 1026
bryos, to a significant extent, because they have a lightsensitive pineal gland (Aige-Gil and Murillo-Ferrol, 1992; Zeman et al., 1992). Recently, a new, low-power, economical light-emitting diode (LED) lamp was introduced to investigate the effect of monochromatic light on turkey and broiler embryonic development by Rozenboim et al. (2003, 2004b). They found that, in ovo, green LED light photostimulation enhanced the embryo development and posthatch growth in female turkeys and both male and female broilers (Rozenboim et al., 2003, 2004b) by promoting skeletal satellite cell proliferation and differentiation in late stages of chicken embryogenesis (Halevy et al., 2006). Nowadays, nutrient composition and meat quality characteristics of poultry products are widespread concerns by consumers. The quality of poultry products varies with growth rate and body composition (Dransfield and Sosnicki, 1999; Duclos et al., 2007). However, there is no information in the literature on whether monochromatic light stimuli that showed growth-promoting effects can also influence breast meat composition and subsequent meat quality. Thus, the aim of this study was to investigate the effect of monochromatic light stimuli during embryogenesis on breast muscle growth, chemical composition, and meat quality of broilers. RESEARCH NOTE Birds. Each hatched chick was weighed, sexed, and tagged. One hundred and 20 male chicks from each treatment group were placed in 6 replicates with 20 birds each. All of the birds were housed under white light(30 lx at bird-head level), with a light schedule of 23L:1D (lights off from 2100 to 2200 h) and given free access to commercial diet and water. The temperature in the chicken house was set at 33 C for the first 7 d and was reduced by 3 C each consecutive week until it reached 24 C. Sampling 1027 On 21, 35, and 42 d of hatch, 1 bird with a BW close to the replicate average BW was selected, weighed, and then killed via exsanguination of the left jugular artery with bistouries. The left breast muscles were removed from the sternum, cleaned of connective tissue, and weighed to calculate the breast muscle percentages of BW. In addition, at 42 d of age, another bird from each replicate was killed with the same procedure, and the entire right pectoralis major of each broiler was sampled for the determination of ph, meat color, drip loss, cooking loss, and shear force value. The left pectoralis muscles were homogenized immediately and subsequently frozen at 80 C for chemical analyses. MATERIALS AND METHODS Light Treatments and Bird Management All experimental procedures were approved by the Animal Care and Use Committee of the Feed Research Institute of the Chinese Academy of Agricultural Sciences. Embryos. Fertile broiler eggs (Arbor Acres; n = 1,320) were preweighed and selected for an average weight of 68.5 g (range = 65 70 g). Eggs were randomly assigned to 1 of 3 treatment groups in 3 modified commercial incubators: 1) control group (in dark condition), 2) monochromatic green light group (560 nm), and 3) monochromatic blue light group (480 nm) for the entire period. The continuous monochromatic lighting systems sourced from LED cold-light lamps and were equalized at the intensity of 15 lx at eggshell level from the first day of incubation until hatching. The light intensity was measured with a digital luxmeter (Mastech MS6610, Precision Mastech Enterprises, Hong Kong, China). Three identical, microcomputer automatic incubators (K12SS-1-BO7, Dezhou Zhicheng Incubation Equipment Co., Ltd., Shangdong, China) were calibrated before hatching the experimental eggs. Incubation conditions were 37.8 ± 0.1 C and 60% RH from d 0 until hatch, and the temperature and RH were recorded every 4 h. Eggs in the incubators were turned through 270 every 1.5 h until d 19. On d 10 of embryogenesis, all eggs were candled, and infertile eggs were removed. Measurements Hatchability and Hatching Weight. During the last 2 d of incubation, hatching occurrences were monitored after every 2 h and hatched chicks were recorded. Hatchability was calculated as (%) = 100 (number of chicks hatched/number of fertile eggs set), where each set layer was taken as a replicate, and 5 layers of each incubator means 5 replicates per treatment. Hatching weight was analyzed by newly hatched chicks in 4 boxes (100 birds per box), and each treatment group consists of 4 replicates. Growth Performance. Average BW, breast weight, breast muscle percentages of BW, and feed conversion ratio (FCR; feed:gain, g:g) were calculated from the day of hatching to 21, 35, or 42 d of age. Chick mortality was also recorded during the feeding trial (from d 0 until d 42 of age). Breast Chemical Analyses. Moisture, CP, crude fat, and crude ash content of breast muscle homogenates were determined using AOAC (2000) procedures. Muscle ph. According to Zhang et al. (2009), muscle ph at 45 min (initial ph, phi) and 24 h postmortem (ultimate ph, phu) was measured using a waterproof spear-type pocket ph meter (ph Spear, Eutech Instruments Pte Ltd., Ayer Rajah Crescent, Singapore). The ph decline within 24 h postmortem (ΔpH) was calculated as ΔpH = phi phu. Meat Color. Meat color was measured in duplicate with a chomometer (Chroma Meter TCP2, Beijing Ao Yi Ke Photoelectric Instrument Co. Ltd., Beijing, Chi-
1028 Zhang et al. na). The CIE-Lab system values of lightness (L*), redness (a*), and yellowness (b*) were recorded at 45 min and 24 h postmortem. Drip Loss. Drip loss was measured as described by Zhang et al. (2009). Briefly, approximately 30 g (wet weight, W 1 ) of regular-shaped muscle from the right pectoralis major muscle was placed in a zip-sealed plastic bag, and then was filled with nitrogen to avoid oxidation, evaporation, and mutual extrusion. All bags were stored at 4 C for 24 h, and then surface moisture of the fillets was absorbed with filter paper and reweighed (W 2 ). Drip loss was calculated as (%) = (W 1 W 2 )/W 1 100%. Cooking Loss. After testing the drip loss, the meat samples were placed in new zip-sealed polyethylene bags and stored at 4 C until 72 h postmortem. At 72 h postmortem, the muscles were dried and weighed (W 1 ), and then heated in a water bath at 85 C for 20 min (end-point temperature of 80 C), cooled in running water to ambient temperature, and then dried and reweighed (W 2 ). Cooking loss was evaluated as (%) = (W 1 W 2 )/W 1 100% (Xu et al., 2011). Shear Force Value. After testing the cooking loss, the cooked meat was equally divided into 2 strips that were 3.0-cm long, 1.0-cm wide, and 0.5-cm thick. Shear force value was tested by using a TMS-Pro Texture Analyzer (Food Technology Corporation Co., Sterling, VA) with a 100-N load cell and a crosshead speed of 150 mm/min. Adjacent strips were cut from the medial portion of the muscle, parallel to the longitudinal axis of the myofibers, and sheared according to the procedure described by Honikel (1998). The muscle was cut perpendicular to the muscle fiber orientation, and each strip was cut 4 times at different locations. The average mean of the 8 cuts was taken as the final result for 1 meat sample. Statistical Analysis Data were presented as means ± SE and subjected to one-way ANOVA using the GLM procedure of SAS version 8.02 (SAS Institute, 2001). Significant differences among treatment means were separated by Fisher s least significant difference multiple-range test. The significance levels were defined as P < 0.05, unless otherwise stated. RESULTS Hatchability, Hatching Weight, and Growth Performance No effects of light stimuli during embryogenesis on hatchability, hatching weight, and bird mortality during the entire trial period were observed in the present study (Table 1). At 21, 35, and 42 d of age, significant increases in the BW and breast muscle weight were observed in birds incubated under green light compared with those of birds incubated under both blue light and dark condition (P < 0.05). The breast muscle weight and breast muscle percentage in birds incubated under green light were significantly elevated by 50.39 g (0.76%) and 54.07 g (1.20%) than those in the dark condition or blue group at 42 d of age (P < 0.05), respectively. In the green light group, feed intake during 0~42 d was higher than that in the other 2 treatment groups (P < 0.05). A lower FCR during 0~35 and 0~42 d in the green light group was also found compared with that in the dark condition (P < 0.05), but no significant difference was observed between the blue and green light groups (P > 0.05). There were no significant differences between the blue and dark treatment groups on all above performance parameters (P > 0.05). Breast Chemical Analysis Table 2 shows the effect of monochromatic light stimuli during embryogenesis on contents of moisture, CP, crude fat, and crude ash in breast muscle of 42-d-old male broilers. No significant differences were found in the contents of moisture and crude ash among treatment groups (P > 0.05), although the green light group showed a trend in increasing CP (88.95 ± 0.35%) and a decreasing trend in crude fat (5.78 ± 0.32%) compared with the dark condition (CP, 88.51 ± 0.41%; and crude fat, 6.01 ± 0.27%, respectively). A relatively higher crude fat percentage was observed in the blue light group in this study. However, there were also no significant differences (P > 0.05) among treatment groups. Meat Quality Both green and blue light stimuli during embryogenesis did not significantly affect breast muscle ph, drip loss, shear force value, as well as the L*, a*, and b* values of 45-min or 24-h meat color (P > 0.05; Table 3). There was a trend toward green light stimuli increasing cooking loss (P = 0.08) and the L* value of 24-h meat color (P = 0.09). DISCUSSION Some of the previous studies reported a growth-promoting effect of monochromatic LED light stimuli during embryogenesis in turkey poults and broiler chickens (Rozenboim et al., 2003, 2004b). Compared with white and dark incubation treatment groups, intermittent green light stimuli enhanced the posthatch BW of female turkeys from 28 d of age until termination of the experiment at 79 d of age, but no growth-promoting effect on males was observed (Rozenboim et al., 2003). For this sexual dimorphism, they speculated that female turkeys are more receptive to in ovo photostimulation by green light as compared with male turkeys. In a similar study on broilers, Rozenboim et al. (2004b) found that chicks incubated under green light and
RESEARCH NOTE 1029 Table 1. Effect of monochromatic light stimuli during embryogenesis on hatchability, hatching weight, and growth performance of male broilers Item Dark Green Blue P-value Hatchability, % 89.55 ± 1.46 90.23 ± 0.79 88.82 ± 1.08 0.807 Hatching weight, 1 g 47.84 ± 0.34 48.01 ± 0.37 47.73 ± 0.39 0.895 Initial weight, 2 g 48.42 ± 0.32 48.63 ± 0.27 48.60 ± 0.35 0.954 Mortality, 3 % 5.00 ± 1.76 5.83 ± 1.54 7.50 ± 2.14 0.706 BW gain, g/bird 0~21 d 734.5 ± 6.0 b 772.6 ± 9.1 a 730.5 ± 7.7 b <0.001 0~35 d 1,829.6 ± 26.4 b 1,969.8 ± 29.9 a 1,840.4 ± 17.2 b 0.003 0~42 d 2,330.8 ± 32.5 b 2,502.5 ± 40.9 a 2,369.6 ± 28.7 b 0.010 Feed intake, g/bird 0~21 d 1,088.1 ± 18.8 ab 1,111.9 ± 13.7 a 1,051.6 ± 11.2 b 0.027 0~35 d 3,171.5 ± 54.3 ab 3,258.9 ± 33.8 a 3,090.8 ± 26.8 b 0.031 0~42 d 4,382.7 ± 47.7 b 4,496.9 ± 42.9 a 4,317.5 ± 52.6 b 0.040 FCR 4 (feed:gain, g:g) 0~21 d 1.48 ± 0.02 1.44 ± 0.02 1.44 ± 0.01 0.188 0~35 d 1.73 ± 0.02 a 1.66 ± 0.01 b 1.68 ± 0.02 ab 0.011 0~42 d 1.88 ± 0.03 a 1.80 ± 0.02 b 1.82 ± 0.02 ab 0.037 Breast muscle weight, g/bird 21 d 120.1 ± 2.1 b 131.9 ± 3.0 a 120.4 ± 1.0 b 0.005 35 d 341.2 ± 13.7 b 375.3 ± 10.1 a 349.2 ± 9.8 b 0.043 42 d 428.6 ± 19.2 b 479.1 ± 16.4 a 425.1 ± 10.2 b 0.039 Breast muscle of BW, % 21 d 15.35 ± 0.26 16.02 ± 0.31 15.46 ± 0.32 0.326 35 d 18.17 ± 0.13 18.58 ± 0.17 18.48 ± 0.28 0.135 42 d 18.02 ± 0.23 b 18.78 ± 0.18 a 17.58 ± 0.19 b 0.019 a,b Means within a row with no common superscript differ significantly (P < 0.05). Results are presented as mean ± SE. 1 Average BW of all hatching chicks (both male and female) of each treatment group. 2 Average BW of 120 selected male chicks from each treatment group. 3 Chick mortality during the feeding trial (from d 0 until d 42 of age). 4 Feed conversion ratio. reared under white light had a significantly higher BW in both male and female birds as early as from hatched day until 42 d of age. They suggested that sexual dimorphism in growth during embryo development was not associated with light stimulation in broilers. In our current study, we found that continuous monochromatic green light (15 lx) stimuli during incubation and being reared under white light (30 lx) significantly increased posthatch BW and breast muscle growth from 21 d of age until 42 d of age, as well as breast muscle percentages from 35 until 42 d of age in broilers. In addition, no significant differences were observed in the hatchability and hatching weight among these 3 treatment groups. These results are more consistent with the findings by Rozenboim et al. (2004b). Moreover, Halevy et al. (1998) reported that green or blue light stimuli enhanced early hatched chick muscle growth by increasing in the number of satellite cells. By a further cell-culture experiment, they confirmed that the stimulatory effect of in ovo monochromatic green light on posthatch muscle growth is the result of enhanced proliferation and differentiation of adult myoblasts and myofiber synchronization (Halevy et al., 2006). Therefore, it is plausible that green light stimulation during incubation enhances the proliferation and differentiation of embryonic myoblasts and subsequent muscle hypertrophy (Halevy et al., 2006). In addition, our study demonstrated that continuous green light stimuli during embryogenesis also significantly increased feed intake and improved posthatch feed efficiency compared with the dark condition, although the effect of light stimuli on these data was not mentioned in the studies of Rozenboim et al. (2003, 2004b). Poultry product quality is closely related to the poultry growth rate, and higher growth rates may induce muscle composition changes, and even fiber morpho- Table 2. Effect of monochromatic light stimuli during embryogenesis on breast chemical composition of 42-d-old male broilers 1 Item Dark Green Blue P-value Moisture, 2 % 76.65 ± 0.26 77.01 ± 0.30 76.73 ± 0.15 0.743 CP, 3 % 88.51 ± 0.41 88.95 ± 0.35 88.40 ± 0.24 0.377 Crude fat, 2 % 6.01 ± 0.27 5.78 ± 0.32 6.29 ± 0.23 0.605 Crude ash, 2 % 5.50 ± 0.11 5.37 ± 0.09 5.41 ± 0.09 0.628 1 Results are presented as mean ± SE. 2 Based on the percentage of fresh muscle weight. 3 Based on the percentage of DM.
1030 Zhang et al. Table 3. Effect of monochromatic light stimuli during embryogenesis on breast meat quality of 42-dold male broilers (mean ± SE) Item Dark Green Blue P-value ph 1 i 6.48 ± 0.01 6.41 ± 0.02 6.45 ± 0.04 0.283 phu 2 5.88 ± 0.02 5.85 ± 0.02 5.83 ± 0.02 0.202 ΔpH 3 0.60 ± 0.02 0.57 ± 0.04 0.62 ± 0.04 0.543 Drip loss, % 1.66 ± 0.08 1.80 ± 0.10 1.65 ± 0.08 0.172 Cooking loss, % 22.21 ± 0.82 24.27 ± 0.89 22.82 ± 0.46 0.079 Shear force value, N 17.03 ± 0.70 16.05 ± 0.85 16.25 ± 0.67 0.515 45-min meat color 4 L* 52.10 ± 0.47 51.97 ± 0.55 50.83 ± 0.49 0.203 a* 16.66 ± 0.82 15.33 ± 1.18 16.90 ± 1.02 0.630 b* 13.71 ± 1.27 15.62 ± 0.97 13.23 ± 0.84 0.338 24-h meat color L* 55.02 ± 0.57 57.84 ± 0.40 55.39 ± 0.45 0.091 a* 8.70 ± 0.85 7.39 ± 0.75 8.30 ± 0.93 0.470 b* 13.35 ± 0.79 13.20 ± 0.79 14.40 ± 0.76 0.439 1 phi = initial ph, the ph at 45 min postmortem. 2 phu = ultimate ph; the ph at 24 h postmortem. 3 ΔpH = phi phu. 4 L* = lightness; a* = redness; b* = yellowness. logical abnormalities (Dransfield and Sosnicki, 1999; Duclos et al., 2007). In the current study, no significant difference among light stimuli groups and the dark condition in the chemical composition of breast meat was observed. Nonetheless, the green light group showed an increasing trend in the content of breast muscle CP and a decreasing trend in crude fat content, whereas the blue light group had a higher crude fat content. Further studies are needed to determine whether green and blue lights are involved in different metabolic regulation on protein synthesis and fat deposition in broilers. Meat quality is a general term to describe the character and perceptions of meat. The ph can significantly affect meat quality. Some studies have reported that breast muscle mainly consists of type II fibers (glycolytic fibers (Zhang et al., 2009), which is negatively related to the early postmortem muscle ph and positively related to drip loss and lightness (Larzul et al., 1997; Ryu and Kim, 2005). Therefore, poultry breast muscle may tend to be pale, soft, and exudative-like when affected by environmental, disease, or nutritional factors. Thus, light stimuli as an important environmental factor might affect breast meat quality. In the present study, light stimuli during incubation did not affect initial ph, ultimate ph, or the 24-h ph decline postmortem of breast muscle. However, there was a trend toward green light stimuli increasing the L* value of 24-h meat color (P = 0.09) and cooking loss (P = 0.08), indicating that green light stimuli may slightly decrease the water-holding capacity of breast meat. Overall, green light stimuli only affect a few of the general meat quality characteristics, and this effect was not significant enough to be detrimental or beneficial to meat quality. 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