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Abstract The objective of this study was to investigate the beneficial effects of early age thermal conditioning and lighting regime in reducing the adverse effects of hot weather conditions, and improving the productive performance of ducks reared under hot ambient temperature. A total of 160, one day -old Muscovy ducklings were used in this study . The brooding temperature was regulated to be kept at 33 o C at the first week by using gas heaters then reduced 2 o C weekly till reached the room temperature. At the first day post hatching all birds were weighted, wing banded and then divided into two equal groups. The control group was maintained under normal ambient temperature while the second group was exposed to early age thermal conditioning (exposed to 39±1°C for 6 h at the 5th day of age and then subjected to normal ambient temperature. The birds of all groups were maintained under continuous lighting program (23h light, 1h dark).During the first week until the fourth week of age. After that, the two groups were divided into two subgroup was subjected to normal day light (16 h light, 8h dark) and the second subgroup was subjected to intermittent light regime of 4h light and 2h dark (make 16h light, 8h dark). The obtained results could be summarized as follows: 1. Early heat conditioning of ducklings increased significantly live body weight and body weight gain compared to control group at 8 and 12 weeks of age. However, the intermittent lighting program lad no effect on both body weight and body weight gain. 2. The overall mean feed intake of Muscovy ducklings was significantly decreased in early heat exposed group compared to the control group at all ages studied. Also, feed conversion ratio the was better in early heat exposed group compared to the control one.3. The lowest value of feed intake was recorded for the intermittent light groups compared to the control group. Also, the intermittent light group had the best feed conversion ratio all ages. 4. The overall means of liver, gizzard, heart and inedible parts weight were significantly increased in early heat exposed group compared to the control group. Also, spleen and thymus had the same trend in early heat exposed group compared to the control group. 5. Carcass and heart weight percentages were significantly increased in intermittent light group compared to the control group. 6. Rectal temperature and respiration rate were significantly lower in early heat conditioning ducks than control ones at 12 weeks of age. 7. Rectal temperature and respiration rate were slightly low, but insignificantly in intermittent light groups compared to control group at 12 weeks of age. 8. Early heat conditioning caused a significant increase in plasma total proteins and globulin levels as compared to control group. Also, values of albumin were insignificantly increased in early heat exposed group as compared to control group. 9. Plasma total protein level was insignificantly increased in intermittent light group compared to continuous light group. While, intermittent light group had significantly increased plasma globulin level compared to continuous light group. 10. Plasma total lipids and triglyceride concentrations of Muscovy ducks were significantly decreased in early heat exposed group compared to the control group at ages studied. 11. Intermittent light program had significantly decreased plasma total lipids and triglycerides concentrations compared to other light group 12. Early heat exposure caused significantly decreased in both AST and ALT activity compared with un-exposed ducks. 13. Intermittent light group had significantly decreased the activity of plasma ALT and AST compared to continuous light group.14. Early heat exposure resulted in an insignificantly increased T3 level compared to control group at 12 weeks of age. Intermittent light group had significantly decreased plasma levels of T 3 compared to continuous light group. Early heat exposure reduced the corticosterone concentration compared with heat-stressed birds. Plasma corticosterone concentration was significantly lower in intermittent light groups compared to control group at 12 weeks of age during heat stress. 15. The blood pH of Muscovy ducks were significantly decreased in early heat exposed group compared to the control group. 16. Intermittent lighting program had significantly decreased plasma the values of blood pH compared to continuous light group. 17. Red blood cells count, hemoglobin content and hematocrit % increased in early heat-conditioning ducks than control birds at 12 weeks of age. Similar results were also recorded for the intermittent light groups. 18. The heterophils and H/L ratio of Muscovy ducks were significantly decreased in early heat conditioning group compared to the control group. While, overall mean lymphocytes count was significantly increased. 19. Heterophils and H\L ratio were significantly decreased for in intermittent light groups compared to control group under early heat conditioning. Also, intermittent light treatment induced a significant increase in total white blood cell count and lymphocyte percentage. 20. The plasma lysozyme concentration of Muscovy ducks were insignificantly increased in early heat conditioning and intermittent group compared to the control group at 12 wks of age. 21. The overall mean malondialdehyde (MDA) contents of Muscovy ducks were significantly decreased in early heat conditioning group compared to the control group. While, the overall mean of SOD and CAT activities were insignificantly increased in early heat exposed group compared to the control group. Intermittent lighting program had insignificantly decreased MDA compared to continuous light group. Also, intermittent light treatment induced a significant increase in superoxide dismutase and catalase enzymes compared to control group. It is concluded that early age heat conditioning of Muscovy ducklings and using an intermittent lighting program could enhance the productive performance and antioxidant status of ducks without adverse effects on blood parameters of ducks during the whole experimental period. |