Comparative effects of Scrophularia striata with synbiotic and antibiotic on performance and immune response of broiler chickens

Following the ban on antimicrobial growth promoters in poultry nutrition in EU and growing pressure on poultry producers in other parts of the world, there is an increasing interest in searching for growth promoting and immune system-strengthening alternatives. Among the possible alternatives, probiotics, prebiotics, synbiotics (combination of probiotic and prebiotic) and more recently phytogenic products are considered interesting because they have acquired more reliability and acceptability among consumers as safe and natural additives. Scrophularia striata (SS) is a plant which grows in the northeastern part of Iran and their immunomodulatory activities of some species of Scrophularia have also been reported by other investigators. Due to the lack of study for Scrophularia striata effects on broilers performance, and the importance of improving the immune status of broilers, this study was conducted to evaluate the effect of S. striata on male broilers growth performance, heterophil to lymphocyte ratio and immunity; and also to compare them with virginiamycin as a well-documented antibiotic growth-promoter. Two-hundred and fifty of one-day-old male (Ross 308) broiler chicks were classified into 25 groups. Each group included 10 chicks (five treatments and five replicates per treatment). The five experimental treatments were as follow: basal diet with no additives (control diet) and basal diet containing virginiamycin antibiotic, synbiotic, 0.4 or 0.8 % SS. Feed intake (FI) and body weight gain (BWG) were recorded in different periods and feed conversion ratio (FCR) was calculated. To study the effects of different treatments on blood leukocyte subpopulations, blood samples of two birds from each replicate were collected from the wing vein at the end of experiment. EDTA-containing blood samples were stained subsequently, 100 leukocytes per samples were counted by an optical microscope. The ratio of heterophil (H) to lymphocyte (L) was calculated. Vaccination was carried out according to the routine regional vaccination program and was based on optimal timing of the maternal antibody level. On 7th and 14th days after last vaccination, blood samples were collected from brachial veins, and the sera were used to determine the humoral immune response derived from vaccination against Newcastle disease and infectious bursal disease. Haemagglutination inhibition tests and enzyme-linked immunosorbent assays were used to determine antibody titers of the chickens against Newcastle disease and infectious bursal disease, respectively. The data were analyzed in a completely randomized design by ANOVA using the General Linear Model (GLM) procedure of SAS Institute. The BWG of broilers receiving the antibiotic diet was higher (P