PERFORMANCE AND HUMORAL IMMUNE-RESPONSE IN HEAT-STRESSED BROILERS FEDAN ASCORBIC-ACID SUPPLEMENTED DIET

A six-week experiment was conducted to investigate the influence of su pplemental dietary ascorbic acid (AA) on, body weight, feed consumptio n, feed conversion and the humoral immune response of broilers exposed to heat stress and inoculated with an inactivated vaccine strain of a vian infectious bronchitis virus (IBV). The four treatment groups cons isted of a control group under no heat stress and receiving no AA supp lementation and three groups consisting of birds maintained at 32C and fed a diet,supplemented with 0, 500 or 1000 ppm AA. Ascorbic acid sup plementation in heat-stressed groups did not improve the body weight c ompared with the heat-stressed, unsupplemented birds. Feed consumption was improved (P less than or equal to.05) for the heat-stressed birds receiving 1000 ppm AA compared with heat- stressed, but no AA supplem entation At the concentration of 1000 ppm AA, feed conversion was not significantly different fron that observed for the control birds. As t he concentration of AA supplementation increased, the relative weight of the bursa of Fabricius also increased During heat stress, birds sup plemented with 500 ppm AA developed increased IBV antibody titers. The serum corticosterone concentration was lowered (P less than or equal to 0.05) in these birds. There was a positive correlation (r(2)=.95) b etween antibody titers and AA concentration and a negative correlation (r(2)=.54) between the serum corticosterone concentration and the ant ibody titers.