Effects of Higher Levels of Zinc Supplementation on Performance, Mineral Availability, and Immune Competence in Broiler Chickens

Two feeding trials were simultaneously conducted utilizing 210 and 140 1-d-old commercial broiler chicks for evaluating the effect of Zn supplementation on performance, mineral availability (experiment I), and immune response (experiment II), respectively, up to 4 wk of age. A basal diet was formulated using corn-soybean meal without supplemental Zn. Six test diets were prepared in which the basal diet was supplemented with Zn at 10, 20, 40, 80, 160, or 320 ppm using ZnSO4·7H2 O. Diets were fed ad libitum to broilers in cages from 8 to 28 d of age. Supplemental Zn did not influence body weight gain, feed intake, feed efficiency, ready-to-cook yields, leg scores, or tibia weight at 4 wk of age. Tibia ash was significantly lower only at 320 ppm level. The percent Ca and P in tibia increased steadily with supplemental Zn up to 80 and 40 ppm, respectively, and decreased thereafter. A linear increase in Zn deposition was observed in bone, liver, and kidney with Zn supplementation. The humoral and cell mediated immune responses were significantly higher at the 80-ppm level compared with lower levels. The heterophil and lymphocyte ratios were narrow, indicating less stress with Zn at 40 ppm and above. The weights of bursa and spleen were higher at 40 ppm compared with lower levels. This study showed that the basal diet Zn (29 ppm) was adequate to support optimum performance of broilers. For better mineral retention, immune response, and alleviation of stress, 80 ppm of Zn was required up to 4 wk of age.