نبذة مختصرة : This study was conducted to evaluate the effects of dietary supplementation of different levels of vitamin C (VC) in broiler chicken reared under high stocking density on the growth performance, blood biochemical parameters and the expression of heat shock protein genes. A total of 150, one day old mixed sex broiler chicks (Cobb 500) were randomly distributed in five equal groups. Group1 was reared in normal stocking density (10.6 birds/m2) and fed on the basal diet (BD) without VC (control). While, chicks in other groups (2, 3, 4 and 5) reared in high stocking density (15.6 birds/m2) and fed on BD supplemented with VC at 0, 200, 400 and 600 mg / kg diet, respectively. Birds reared in high stocking density showed a reduction of the final body weight and total feed intake, with high mortality (6.6%). Moreover, they revealed a significant up-regulation of HSP70 mRNA and elevated HSP90 and HSF1 mRNA expression in heart and liver tissue. Graded dietary levels of VC provided variable protection against the hazard of high density through improved final body weight and total feed intake, decreased the mortality % and downregulated liver HSP70 expression level. However, the best performance was observed in birds supplemented with 200 mg/kg VC (group 3). Key words: chicks' growth performance; gene expression; stocking density; vitamin C
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