Similar to our results, Rozenboim et al. (2004a) reported that on the tenth day of the experiment in which they applied monochromatic lighting, the body weight averages of the broilers, which were switched from green to blue, were higher than the averages of the other experimental groups on the 46th day. In this study, the fact that the GB group had a higher body weight average than the other single, combined, and mixed groups were determined by Rozenboim et al. (2004a), Guevera et al. (2015), and Olanrewaju et al. (2016) was found to be consistent with the results reported. Rozenboim et al. (2004a) reported that the live weight averages of the chickens, which were applied to a monochromatic lighting program with a transition from green to blue on the tenth day of the experiment were higher than the averages of the other experimental groups at 46 days of age. In this study, the fact that the average values of body weight of the GB group had higher than the other single, combined, and mixed groups were found to be consistent with the results reported by Rozenboim et al. (2004a), Guevera et al. (2015) and Olanrewaju et al. (2016).
In a study carried out by Karadavut et al. (2017), growth samples of Japanese quails treated with white, red, green, yellow monochromatic lighting were analyzed with Gompertz, Broody, and Von Bertalanffy nonlinear regression models. According to the goodness-of-fit criteria, the Gompertz growth model was found to be the best-fitted model, but estimation values of model parameters were not presented in their study (Karadavut et al. (2017). Moreover, to our knowledge, there is no study in the literature on the effects of monochromatic lighting applications on the growth curve parameters of broiler chickens. While the average values (6797.61-7174.42 g) of estimations of β0 parameters for treatment groups in this study were higher than the mean values of β0 parameters (5453.80-6282.35 g) reported by Topal and Bölükbaşı (2008), who analyzed the growth samples of female and male broiler chickens using the Gompertz growth model. In addition, the mean values of β1 parameters (5.09–5.85) were found to be similar to the β1 averages (4.91–5.31) reported by Topal and Bölükbaşı (2008). Demuner et al. (2017) who modeled the growth samples of Ross, Cobb, and Hubbard broiler genotypes up to 56 days of age with the Gompertz function, reported that the mean values of the β0 parameter were between 6401–7009 g, similar to the results of this study. Analyzing the growth data of commercial chickens raised in an alternative system up to 56 days of age with the Gompertz model, Marcato et al. (2008) reported that the mean values of the β0 parameter for Ross and Cobb genotypes were 6627.84 g and 6812.30 g, respectively.
According to the results of this study, it was determined that the broiler chickens in the G and GB groups had higher mean values of mature weight parameter, and similarly mean values of the weight of inflection point in the G and GB groups were higher. The mean values of body weights of the broilers at 42 and 56 days of age treated with continuous green monochromatic lighting were lower than those of the GB group (P < 0.05). However, there is no difference between the averages of the G and GB groups in terms of the mature weight parameter of the Gompertz growth curve. It is thought that this surprising situation arises because the green light applied in the G group after the inflection point suppresses the growth.
Sultana et al. (2013a) conducted a study investigating the effects of blue, green, yellow, and white monochromatic lighting on behavior traits and fear responses in ducks. They reported that ducks treated with yellow and white lighting had higher tonic immobility durations than those blue and green monochromatic lighting groups. In a study conducted by Sultana et al. (2013b), it was determined that chickens raised under red LED light had longer tonic immobility times. In that study, it was determined that there was no difference between the tonic immobility duration of chickens in the green LED group and the control groups with incandescent bulbs. In addition, it has been reported that blue monochromatic lighting reduces the tonic immobility duration. Researchers suggested that a light wavelength in the range of 440–570 nm would reduce fear responses in chickens (Sultana et al., 2013b). Mohamed et al. (2016) also reported that mulard ducks reared with white and red lighting had longer tonic immobility durations than those reared with green and blue lighting. Researchers stated that ducks illuminated with green and blue monochromatic lights had lower fear levels. Mohamed et al. (2017) investigated the effect of monochromatic lighting on the fear level of broiler chickens, reported that the fear level of chickens with green and blue monochromatic lighting was lower.
In this study, when the effects of different monochromatic lighting applications on the fear level of broilers were examined (Table 2), it was determined that the highest average of tonic immobility time (182.22 sec) was in the BG group (P < 0.05). The mean values of duration of tonic immobility in broilers treated with continuous blue, continuous green, and blue-green alternating monochromatic lighting were found to be lower than those of the other groups (P < 0.05). These results were consistent findings with the for ducks and broilers by Sultana et al. (2013a, b), Mohamed et al. (2016, 2017). The shorter tonic immobility period of broilers reared under blue and green light may be due to the calming effect of these light colors (Prayitno et al. 1997), and birds become less active and less aggressive under these conditions (Mohamed et al. 2016). In the study, the highest mean value of tonic immobility duration was measured in broilers that were exposed to intermittent blue-green light every five minutes. It is thought that the application of intermittent lighting causes fear and anxiety in birds.
In birds, high levels of fear of humans cause a decrease in egg production, worsening in growth and feed efficiency, adversely affecting product quality and decreasing reproductive activities as well as increasing aggression, coping difficulties, and suppression of the immune system (Barnett et al, 1993; Gross and Siegel 1982; Jones 1996). Visual or physical contact with humans may cause behavioral inhibition, withdrawal, panic, and violent escape reactions in chickens as a result of adrenal responses, and in some cases, injury and deformation may occur (Jones 1996). Fear reactions, such as panic or violent escape attempts, not only waste energy and therefore incur a metabolic cost, but can also cause death in birds due to squatting and entrapment (Waiblinger et al., 2006).
In the emergence test, the mean values of passive duration of broiler chickens in different experimental groups varied between 74.42 seconds and 94.08 seconds, and there was no statistical difference between the groups (P > 0.05). Similarly, the application of different monochromatic lighting did not affect the percentage of active birds, and the ratios of active animals varied between 40.00% and 52.50% (P > 0.05). As can be seen from Table 5, in terms of the ratio of passive birds, the chickens with conventional lighting in the control group and the chickens with intermittent lighting in MBG group had the lowest mean values (22.50% and 23.75%, respectively, P < 0.05). In terms of the ratio of active animals, the mean values of the chickens in the control group and the intermittent lighting group were found to be higher than those of the other groups (37.50% and 32.50%, respectively, P < 0.05). This supports the view reported by Khaliq et al. (2018) and Hesham et al. (2018) that broilers reared under blue and green light are calmer. In addition, similar to the tonic immobility test results, it is thought that intermittent lighting causes fear and anxiety in animals, and the number of passive animals is low, and the number of active animals is high for the same reason in this experimental group. As can be seen in Table 6, there was no statistical difference between the groups in terms of the percentages of birds exhibiting avoidance and inspection behaviors (both P > 0.05). In addition, within the scope of the researcher’s test behind the box, no fear behavior was observed in the animals in the experimental groups. These results show that this test is not very sensitive in measuring fear responses.
It is already known that green monochromatic lighting accelerates muscle growth and stimulates early growth (Halevy et al., 1998). In a study conducted by Soliman and Hassan (2019), it was claimed that the blue monochromatic lighting increased the secretion of metabolic hormones and significantly improved carcass weight and some performance traits compared to conventional white and red monochromatic lighting. Bayraktar and Altan (2005), who compared different light sources and blue and green LED lighting in broilers, reported that the carcass yield of chickens with blue and green LED lighting was higher than those of other groups. In a study by Mohamed et al. (2017), broiler chickens were treated with white, green, and blue monochromatic lighting. Researchers claimed that birds treated with white monochromatic lighting had higher average values (1400 g and 71.30%, respectively) in terms of both carcass weight and carcass yield. The results of this study, which are inconsistent with our study results and many other studies, are thought to be due to the animal material used. As can be seen from Table 7, the mean values of breast weight and back-neck weight of the broilers treated with green monochromatic lighting in the first ten days of the fattening period and then with blue monochromatic lighting were found to be higher than those of the other lighting groups (P < 0.05). Cao et al. (2008) who applied different monochromatic lighting programs in broilers, reported that the weights of carcass, breast, and thigh of broilers exposed to blue monochromatic lighting were higher than those of other groups. In addition, Ke et al. (2011) claimed that the carcass yield of broilers treated with blue monochromatic lighting was higher than those using green, white, and red monochromatic lighting. However, Liu et al. (2010) observed that birds reared under green monochromatic light had higher breast muscle weights than those of birds with blue, red, and white lighting.
Rozenboim et al. (2004a) and Classen et al. (2004) determined that green monochromatic lighting can increase the growth of young broilers more, while blue monochromatic lighting is more effective after the first period and warns the birds about growth. In this study, it was determined that broiler chickens treated with green monochromatic lighting for the first ten days and then blue monochromatic lighting had higher averages in terms of both growth performance and slaughter-carcass characteristics. When the findings of the tests performed to determine the fear state of the chickens were examined, it was determined that the worst results were in the intermittent lighting group (MBG), in which a blue and green light conversion was applied every five minutes. The second worst results were also found for broilers treated with green-blue combined monochromatic lighting (GB). As a result, it was determined that the application of green monochromatic lighting in the first ten days of the fattening period and blue monochromatic lighting in the following period positively affected growth and slaughter-carcass characteristics in line with the findings reported by Rozenboim et al. (2004a) and Classen et al. (2004). However, it was determined that broiler chickens reared under green-blue combined monochromatic lighting had high fear levels.