# Research Progress and Effects of Light on Poultry Circadian Rhythm Regulation Based on CiteSpace
## 4 Light Affects the Circadian Rhythm in Poultry by Regulating Melatonin Levels
### Effects of Light on Melatoninin  
The disorder of melatonin secretion can affect circadian rhythm, exercise, body temperature, immunity, and other physiological activities [50; 51; 52]. The interference of artificial light at night can affect the production of melatonin. Studies have shown that even very low-intensity night light can reduce melatonin expression and that the degree of inhibition is proportional to the intensity of night light [53; 54]. In addition, light duration remarkably affects melatonin content. It was shown that compared with constant lighting of 24 L:0D, intermittent lighting of 16 L:2D:1 L:2D:1 L:2D and 17 L:3D:1 L:3D produced higher melatonin levels in broiler chickens [34].  
Constant lighting was found to inhibit melatonin levels by reducing arylalkylamine N-acetyltransferase (Aanat) activity [69]. Monochromatic light at different wavelengths also affects melatonin expression (Figure 6), and Aanat is the rate-limiting enzyme for melatonin synthesis [70]. The increase in its content can promote the synthesis of melatonin, and the content of Aanat is affected by positive and negative clock genes [71]. Studies have shown that green light promotes the expression of cAanat genes by increasing the expression of positive clock genes (cClock, cBmal1, cBmal2) [72; 73; 74], thereby promoting the secretion of melatonin in chicken [75; 76; 77]. On the contrary, the expression of the positive clock gene is weak under the red light condition, which weakens the expression of cAanat and reduces the melatonin level of chickens reared under red light [75].  
Creb can promote the secretion of Aanat, and the phosphorylation of Creb increases the mRNA content of Aanat by about 100 times [71]. Moreover, [PERSON] et al. found that the mRNA content of cCreb in broilers reared under green light increased and promoted the secretion of melatonin. The decrease in mRNA content has the opposite effect on melatonin levels. Furthermore, the influence of monochromatic light on melatonin in the chicken embryo period is different from that in the juvenile period. Studies have found that the melatonin rhythm during incubation under red and white light was the highest, whereas the melatonin rhythm in green and blue light was the lowest. Postembryonic exposure  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Poultry Types** & **Parameters** & **Role of Melatonin** & **Reference** \\ \hline \multirow{2}{*}{Quail, chicks, broiler chicken} & \multirow{2}{*}{Growth regulation} & Promote the secretion of somatostatin growth hormone and the promotion of growth & [55; 56; 57] \\  & & & Reduce ascites and sudden death syndrome & [49] \\ \hline \multirow{2}{*}{Broiler chicken} & \multirow{2}{*}{Disease control} & Increase antibody, leukocyte, and lymphocyte formation & [58; 59; 60; 61] \\  & & & Improve & Improve \\ \hline \multirow{2}{*}{Laying bird} & \multirow{2}{*}{Welfare improvement} & Improve & [62] \\ \hline \multirow{3}{*}{Chicken} & \multirow{2}{*}{Reproduction function} & Promote granulocyte cell formation, enhance follicle growth and exert an amelioration of the ovary & [45; 63; 64; 65] \\  & & & oxidative stress & \\ \hline \multirow{2}{*}{Chicken} & Cryopreserved chicken sperm & Improvement of quality & [66] \\ \hline \multirow{2}{*}{Chicken} & Feed conversion ratio & Improve & [67] \\ \hline \multirow{2}{*}{Laying hen} & Egg weight & Increase & [58; 67] \\ \hline \multirow{2}{*}{Broiler chicken} & \multirow{2}{*}{Heat stress} & Reduce the side effects of heat stress and reduce the mortality rate & [68] \\ \hline \multirow{2}{*}{Chicken} & \multirow{2}{*}{Embyrotoxicity} & Protect against the benzo(e)pyrene embryotoxicity & [51] \\  & & & embryootoxicity & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Regulation of melatonin on poultry growth and development, animal welfare, and immune level.  
to green and white light induced an increase in melatonin biosynthesis. It is indicated that rhythmic melatonin biosynthesis can transfer ambient light information to poultry embryos [78].