Effects of monochromatic light on thyroid hormone and endoplasmic reticulum stress-related signaling in broilers.

Thyroid hormones (TH) are pivotal regulators of poultry growth and development. However, the effects of monochromatic light on thyroid function in broilers remain unclear. Therefore, newly hatched Arbor Acre (AA) broilers were randomly reared under white light (WL, 400-700 nm), red light (RL, 660 nm), green light (GL, 560 nm), and blue light (BL, 480 nm) until 42 days. The results showed that compared with WL, RL reduced thyroid weight and elevated serum free triiodothyronine (FT3) levels, whereas GL produced no significant alterations in thyroid weight or circulating TH levels. In contrast, BL increased thyroid weight and thyroid index and decreased serum triiodothyronine (T3) and FT3 concentrations. Furthermore, thyroid hormone synthesis-related genes were slightly upregulated in RL compared with WL, although these changes were not statistically significant. Conversely, BL downregulated the expression of thyroid hormone synthesis-related genes, including thyroid-stimulating hormone receptor (TshR), thyroid transcription factor 1 (Ttf1), sodium-iodide cotransporter (Nis), and thyroid peroxidase (Tpo), and decreased type 2 deiodinase (Dio2) protein expression. Moreover, endoplasmic reticulum (ER) stress-related markers were slightly decreased in RL but elevated in BL, which activated the PERK-eIF2α-ATF4-CHOP pathway and was associated with oxidative stress and increased Bax expression. These findings suggest that monochromatic light affects thyroid function in broilers, and BL exposure is associated with altered thyroid hormone synthesis and ER stress-related signaling.