Abstract
Effects of different photoperiod regimens on the cellular and humoral immunity in broiler chickens were studied(Exp 1). Total one hundred ninety two one-day-old commercial broiler chicks(Cobb$\times$Cobb) were raised between constant lighting(CL) and intermittent lighting (1h light: 3h darkness(IL; 1l; 3D) Body weight, feed intake and feed conversion were measured for seven week. Peripheral blood and splenic lymphocyte activities were tested at 3 and 5 wk of age by performing a mitogen cellproliferation assay with a polyclonal T-cell mitogen, concanavalin A (Con A), and B-cell mitogen, lipopolysaccharide (LPS). To investigate the effect of photoperiod on the humoral immunity, chicks were immunized with sheep red blood cell(SRBC) and iinactivated Newcastle disease virus(NDV) vaccine. Total immunoglobulin G(IgG) concentration was also determined. Diurnal change of melatonin was tested in sera. In experiment 2, 0.1ml melatonin were subcutaneously injected from three to five weeks old if immunomodulation effect of lighting regimen was due to the melatonin or not. Injections of melatonin were made at 0700h and the dosage was 10ng (M2), 100ng(M3), 1$\mu\textrm{g}$(M4) per bird daily, respectively. control were quivalent injections of vehicle(M1). Lymphocyte activities were tested and humoral immunities were examined at 5 weeks of age. Blood melatonin concentration was determined at 0h, 1, h, 2h, and 3h posterior to injection at five weeks old. It was higher in CL chicks than IL chickens during the subsequent period of 3 to 5 wk of age. However, weight gain of chicks raised IL were significantly higher at 6 wk of age than CL(P<0.05). Antibody response to NDV was not affected by both photoperiod regimens and melatonin injection, whereas anti-SRMB titer and IgG concentration were enhanced. Lymphocyte activity of chickens raised under IL was sighificantly higher than those of chickens raised under CL. Melatonin injection also increased lymphocyte activity. When peripheral blood lymphocytes were used, proliferation response to LPS and Con A were significantly increased in M2 and respectively. The results of this experiments suggest that IL improved host immune response and melatonin have immunomodulatory roles.
