Enhancement of cellular and humoral immunity following embryonic exposure to melatonin in turkeys (Meleagris gallopavo)

Two experiments were performed to determine the effect of in ovo melatonin supplementation on the ontogeny of immunity in the Large White turkey poult. Different levels of melatonin were injected into the air cell of the egg 4 days prior to hatch. In Experiment 1, turkey embryos received 3 ml of solution containing 200, 100, 50, 25, 10, or 1 μg/ml of melatonin. The hatchability at each dose was determined and compared to vehicle-injected controls. In Experiment 2, only poults from melatonin treatments in Experiment 1 that resulted in normal hatchability (10 and 1 μg/ml) were used. Lymphoproliferative responses to phytohemagglutinin (PHA-P) and primary antibody responses to Chukar red blood cells (CRBC) were determine at five time intervals: 0, 1, 7, 14, and 21 days post-hatch. At each of these times, including 28 days post-hatch, treatment effects on body weights were determined. At 28 days post-hatch, bursal, thymic, and splenic weights were obtained. In ovo melatonin administration significantly accelerated (P ⩽ 0.05) the development of cell-mediated (PHA-P) and humoral (CRBC) immune responses, and these responses were significantly elevated above vehicle-injected controls through 21 days post-hatch. No effect was observed on bursal, thymic, splenic or body weights. These data suggest that embryonic exposure to melatonin enhances post-hatch immune development and responsiveness.