Effects of Photoperiod Change on Melatonin Secretion, Immune Function and Antioxidant Status of Cashmere Goats

The photoperiod affects animals' secretion of hormones, especially melatonin (MLT), which is involved in the regulation of the immune function and antioxidant status. The present experiment was conducted to study the effects of the photoperiod on MLT secretion, immune function, antioxidant status and related gene expression in goats. Eighteen adult female cashmere goats were randomly divided into three photoperiod groups: the control group (CG: natural photoperiod); the short-day photoperiod group (SDPP group: 8 h light; 16 h dark) and the shortening-day photoperiod group (SIPP group: lighting time shortened gradually from 16 h/d to 8 h/d). The experiment lasted for 60 days. The results showed that SDPP increased MLT concentration in serum at day 30 of the experiment (p < 0.05), but SIPP increased it at day 60 (p < 0.05). The activity of total superoxide dismutase (T-SOD), glutathione peroxidase (GPx) and catalase (CAT) increased (p < 0.05), and malondialdehyde (MDA) concentration decreased (p < 0.05) at day 30 in SDPP; no significant effects of SIPP were observed at day 30. Both SDPP and SIPP goats had higher activities of T-SOD, GPx and CAT (p < 0.05) at day 60. The concentration of immunoglobulin G (IgG), interleukin 1β (IL-1β) and interleukin 2 (IL-2) increased in SDPP (p < 0.05) at day 30. Both SDPP and SIPP raised the concentration of IgG, IL-1β and IL-2 at day 60 (p < 0.05). For the relative gene expression, the SDPP improved the gene expression of SOD1, CAT, GPx4, nuclear factor erythroid-2-related factor 2(Nrf2), IL-1β, IL-2 and tumor necrosis factor-α (TNF-α) (p < 0.05) in blood leukocytes at day 30. In addition, at day 60, goats in the SDPP group had a higher gene expression of CAT, GPx4, IL-1β and IL-2 (p < 0.05). Goats in SIPP had significantly higher gene expression of SOD1, CAT, GPx4, Nrf2, TNFα, IL-1β and IL-2 (p < 0.05) than those in CG. These results indicated that SDPP and SIPP could secrete more MLT and then improve the immune function and antioxidant status of the goats.