Effect of Probiotic Thepax® and Dietary Protein Level on the Performance of Broiler Chicks

This experiment was conducted to compare the effect of probiotic thepax® in diets with different quantities of protein on the performance of Cobb-500 broiler chickens and their serum antibody level against Newcastle disease vaccine (NDV). Two basal diets were formulated based on NRC (1994) recommendations which had NRC (sufficient protein diet) and 90% NRC (low protein diet) for protein. The basal diets were then supplemented with 0 and 0.1% probiotic, resulting in a 2×2 factorial arrangement with 2 levels of probiotic (0 and 0.1%) and 2 levels of protein (NRC and 90% NRC). Each of the 4 dietary treatments was fed to six replicate groups of 20 chicks. The results of experiment showed broilers fed low protein diet without supplementation of probiotic had lower performance than other treatments. Supplementing low protein diet with 0.1% probiotic significantly improved body weight gain and feed conversion ratio, as did those which were fed diets with sufficient quantities of protein. Reducing dietary protein level increased abdominal fat content, but had no significant effect on other carcass composition. Supplementing of probiotic significantly reduced abdominal fat percentage (P<0.05). The utilization of probiotic in low protein diet resulted in increasing serum antibody level against NDV, but sufficient protein diet produced no such effect. Also, the results of experiment indicated that probiotic added to low protein diet improved broilers performance and immune response. However, these effects were not observed in adding probiotic to diet with sufficient quantity of protein.