Performance and Humoral Immune Response in Heat-Stressed Broilers Fed an Ascorbic Acid Supplemented Diet

Tuekam, T.D., Miles, R.D. and Butcher, G.D. 1994. Performance and humoral immune response in heat stressed broilers fed an ascorbic acid supplemented diet. J. Appl. Anim. Res., 6: 121–130. A six-week experiment was conducted to investigate the influence of supplemental dietary ascorbic acid (AA) on body weight, feed consumption, feed conversion and the humoral immune response of broilers exposed to heat stress and inoculated with an inactivated vaccine strain of avian infectious bronchitis virus (IBV). The four treatment groups consisted of a control group under no heat stress and receiving no AA supplementation and three groups consisting of birds maintained at 32C and fed a diet supplemented with 0, 500 or 1000 ppm AA. Ascorbic acid supplementation in heat-stressed groups did not improve the body weight compared with the heat-stressed, unsupplemented birds. Feed consumption was improved (P<0.05) for the heat-stressed birds receiving 1000ppm AA compared with heat- stressed, but no AA supplementation. At the concentration of 1000 ppm AA, feed conversion was not significantly different from that observed for the control birds. As the concentration of AA supplementation increased, the relative weight of the bursa of Fabricius also increased. During heat stress, birds supplemented with 500 ppm AA developed increased IBV antibody titers. The serum corticosterone concentration was lowered (P<0.05) in these birds. There was a positive correlation (r2=.95) between antibody titers and AA concentration and a negative correlation (r2=.54) between the serum corticosterone concentration and the antibody titers.