In this study, we investigated the effects of LED illumination color on the growth, carcass characteristics, serum components, and behavior of fattening pigs housed in a windowless pig pen. Four groups were established based on the installed LED lighting color: blue, green, red, and no lighting.During the growth stage, the red group exhibited the highest daily weight gain, and there was also a significant difference in daily weight gain between the red and no-lighting groups (P < 0.05). In terms of backfat thickness, the blue group showed the lowest thickness in the shoulder and loin, which tended to be thinner than that of the red group in the shoulder (P < 0.10). Additionally, a significant difference was observed between the blue and green groups in the loin (P < 0.05). Furthermore, the no-lighting group showed the highest serum concentration of α-globulin, and there was a significant difference in α-globulin concentration between the no-lighting group and the green or blue groups (P < 0.05). The serum triglyceride concentration was higher in the blue group than in the no-lighting group (P < 0.10). Meanwhile, the green group displayed the highest total cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) cholesterol concentrations, significantly differing from the red group (P < 0.05), while also tending to be higher than the no-lighting and blue groups (P < 0.10) in terms of total cholesterol. Additionally, the green group tended to have higher HDL-cholesterol levels than the blue group (P < 0.10). Notably, the green group showed a significant difference compared with the red group in HDL-cholesterol (P < 0.05) and tended to have higher levels than the no-lighting group (P < 0.10) in terms of LDL-cholesterol. Regarding the fatty acid composition of the perirenal fat, the red group had significantly higher C18:1 levels than the no-lighting and green groups (P < 0.05) and tended to be higher than the blue group in fatty acid composition (P < 0.10). Conversely, the red group had lower C18:2 levels than the no-lighting group (P < 0.10). As for drinking behavior, the red group recorded the lowest scores during the growing and finishing stages, while significantly differing from the green group during the growing stage (P < 0.05) and from the blue group during the fattening stage (P < 0.05). In the dog sitting posture, the green and red groups scored the highest during the growing stage, with significant differences between the red or green groups and the no-lighting group. Moreover, the red group’s score tended to be higher than that of the blue group (P < 0.10), and the green group scored the highest during the finishing stage, with a tendency to be higher than the no-lighting group (P < 0.10). The concentrations of accumulated cortisol were also significantly higher in the green and red groups than in the no-lighting group (P < 0.05).

Overall, these results suggest that the presence or absence of illumination and the color of illumination may significantly affect the growth, carcass traits, and lipid metabolism of pigs. Specifically, red and green illumination may induce more stress in pigs during rearing compared to non-illumination.