Effect of Dietary Ascorbic Acid on Performance and Immune Response of Heat Stressed Broiler Chicks

This study was conducted to evaluate the effect of different levels of ascorbic acid on broiler chicks performance and humoral immunity of Newcastle disease under high environmental temperature. One hundred and twelve, day-old commercial broiler chicks (Hubbard) were reared during summer in an open deep litter experimental house. Four level of ascorbic acid 0(control), 150,350 and 550 mg/kg were fed from day 14to day 42. Feed intake, weight gain, feed conversion ratio, and dressing percentage were measured. Total white blood cells, lymphocytes, heterphils, monocytes, basophils, esinophils were determined. On day 42, thymus, spleen and bursa of fabricius were collected, weighed and expressed as a percentage of live weight. Antibody titers against Newcastle virus were elevated. Significantly (p≤0.05) higher feed intake was observed in birds fed low (150mg/kg) and moderate (350mg/kg) levels of ascorbic acid compared to those fed high level (550mg/kg), which resulted in significant (p≤0.05) improvement in body weight and feed conversion ratio of the moderate and high levels. Dressing percentage was not significantly (p≥0.05) affected by different level of ascorbic acid. Total white blood cells were reduced as the level of ascorbic acid was increased. Lymphocytes increased significantly (p≤0.05) in birds fed moderate (350mg/kg) or high (550mg/kg) levels of ascorbic acid. Heterophils were decreased significantly (p≤0.05) in the group fed the moderate level (350mg/kg) or high level (550mg/kg) of ascorbic acid. Monocytes decreased significantly (p≤0.05) in the groups fed the high level (550mg/kg). However, basophils and esinophils were not significantly (p≥0.05) affected by the different levels of ascorbic acid. The mean weight of lymphoid organs or the ratio of lymphoid organs to body weight were not significantly different (p≥0.05) between the different treatments. Antibody titer against Newcastle virus was significantly (p≤0.05) increased in birds fed diets supplemented with different levels of ascorbic aci