THE EFFECT OF VARYING DIETARY CONCENTRATIONS OF VITAMIN-A ON IMMUNE-RESPONSE IN THE TURKEY

1. The effect of dietary vitamin A on antibody production and T-cell p roliferative response was determined in poults from 21 to 41 d old. Po ults were fed on soyabean meal-sorghum-based diets with concentrations of supplemented vitamin A from 0 to 13.2 mu g/g retinol equivalents f rom hatching and were immunised with Newcastle disease virus (NDV) and turkey pox vaccines. T-cell proliferation response to concanavlin A w as determined in vitro at 31 d old. Antibodies to NDV and turkey pox i n serum were determined at 10 and 20 d after inoculation. 2. Poults re ceiving the diet with no added dietary vitamin A died by 22 d and had very low concentrations of plasma and liver vitamin A. 3. Increasing d ietary concentrations of vitamin A enhanced the proliferative response until the diet contained 6.0 mu g/g, above which the response began t o decrease. The antibody titres to NDV and turkey pox increased as die tary vitamin A increased, with maximal values found 10 d after inocula tion with 6.0 mu g/g. At 20 d after inoculation low antibody titres we re found with low vitamin A intake. 4. These data suggest that maximal immune responses in the poult may be achieved at dietary intakes of v itamin A at or higher than those recommended by NRC (1984, 1994).