The main objective of this study was to investigate the beneficial effects of early age epigenetic adaptation of newly hatched ducks on their post hatch growth performance, physiological and blood biochemical changes, along with oxidative stress and immune responses. Total of 200, day old ducklings were brooded at 33 ±1°C for the first three days post hatching, and then were divided into two equal groups (100 chicks each), a control group maintained under the brooding temperature, while the other group was exposed to early age thermal conditioning at 39.5 ±1°C for 4 h at the 4th, 5th and 6th days post hatching. After that both groups were subjected to 30 ±1°C from the 7th to the 10th day of age then reduced gradually to reach 24 ±1°C by day 28 of age. From the beginning of the 5th week of age until the end of the experiment (12 weeks), all birds have similar feeding and managerial conditions. Blood samples were collected after 24 hours of the first exposure time, and again after the last exposure (at 80 days of age). Results showed that LBW and BWG of ducks were significantly (P ≤ 0.05) higher for those exposed to TM compared by those of the control (TN) treatment. Feed consumption was not significantly affected by early age TM; however, the cumulative FC was significantly increased for the heat-exposed ducks. Meanwhile, feed conversion ratio (FCR) was significantly better for the TM- exposed ducks than those of TN ones. Body temperature and respiration rate were significantly decreased at the latter stage of growing period (12 week) by early-age thermal conditioning. Plasma lysozyme activity of Muscovy ducks was insignificantly increased in early heat exposed group compared to the control one.Redblood cells count, hemoglobin level and PCV were significantly increased in TM exposed ducks compared to the TN ones. Plasma thyroid hormones (T3, T4) and corticosterone levels were significantly increased at the end of experiment as a result of thermal conditioning. A similar trend was also observed for the H:L ratio which was the highest in TN birds. Corticosterone and Heterophils: lymphocytes ratio decreased in the thermally manipulated-duckling compared to control group. Plasma MDA was significantly decreased in early heat exposed group compared to the control group. Superoxide dismutase and catalase enzymes increased in TM exposed ducks compared to the control one. It is concluded that a 3 days of early age thermal conditioning could be used as a practical approach to alleviate the negative impact of heat stress at older ages, to improve the antioxidative status and immune responses in growing ducks.