Effect of dietary ascorbic acid supplementation on performance, behaviour and gene expression in heat-stressed broiler chickens

The objective of the study was to investigate the effects of dietary ascorbic acid on performance, behaviour and gene expressions for heat shock protein70 (HSP70) and catalase (CAT) in the liver, HSP70, toll-like receptor 4 (TLR4), and cholecystokinin (CCK) in the intestine and proinflammatory cytokines (IL-4, IL-6, IFN-gamma and IL1-beta) in the spleen of heat stressed broiler chickens. Ninety-six one-d-old birds were randomly assigned to one of four treatment groups; 1) control group fed basal diet, 2) ascorbic acid group (AA) fed basal diet with ascorbic acid (200 mg/kg ration), 3) heat stress (HS) group fed with basal diet, and 4) heat stress (HSA) group fed basal diet with ascorbic acid. Heat-stressed birds were exposed to temperatures of 34 degrees C for three d from d 21 through d 24. Results indicated that heat stress decreased final body weight, weight gains, decreased feeding, standing idle, walking and preening behaviours and increased drinking, crouching and comfort behaviours compared to the control group. Also, it increased expression of HSP70 in liver and intestine, CAT in liver, TLR4 and CCK in intestine of heat stressed broilers as compared to the control. Additionally, gene expression of splenic cytokines, IL-4, IL-6, and IFN-gamma were also increased in heat stressed birds as compared to the control. In general, ascorbic acid supplementation did not improve body weight or weight gain as compared to the control. Supplementation of ascorbic acid to the HSA group significantly increased feeding, standing idle, walking and preening behaviour than in the HS group; it also led to significant decrease in crouching and comfort behaviours and decreased gene expression levels of CCK, IL-4, IL-6, and IFN-gamma of heat stressed broilers compared to heat stressed birds fed basal diet. Based on these results, adding of ascorbic acid appears to reduce the negative impacts of a short-duration heat stress.