comparative effects of scrophularia striata with synbiotic and antibiotic on performance and immune response of broiler chickens

introduction: 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. materials and methods: 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. results and discussion: the bwg of broilers receiving the antibiotic diet was higher (p<0.05) than the control and 0.8% ss groups at age of 11 to 24 days. compared to the control, feeding synbiotic, 0.4% ss and 0.8% ss also decreased (p<0.05) fi at age of 11 to 24 days. however, there were no significant differences in bwg and fcr among treatments during the overall experiment. when broilers were 25 to 42 days of age, supplementing the diet with antibiotic or synbiotic significantly decreased fcr compared with control and 0.4% ss treatments. moreover, all dietary treatments reduced (p<0.05) overall fcr compared with control treatment, where the broilers fed antibiotic diet had best fcr. the results of the present study also showed that blood lymphocyte percentage was greater and heterophil to lymphocyte ratio was lower in antibiotic, synbiotic and 0.8% ss groups compared to control group. supplementing the basal diet with 0.8% ss increased (p<0.05) the relative weights of thymus and bursa of fabricius at age of 42 days. the birds fed synbiotic or 0.8% ss treatments had also higher secondary antibody titers against newcastle and gamboru vaccines (p<0.05). however, relative spleen weight and primary antibody response were not affected by dietary treatments. a higher bwg observed in broilers fed antibiotic during the days 11–24 which was not reflected at slaughter age might be due to this fact that nutrient requirements of older birds decrease with age and also they have a well developed digestive tracts and organs. the most efficient fcr in broilers fed diets supplemented with all additives revealed that the impact of growth promoter substances, such as synbiotic and phytogenic products, on performance could be associated with a more efficient use of dietary nutrients, which in turn resulted in an improved fcr. the improvements in broilers fcr by synbiotic and 0.4% ss had similar magnitude to the ones determined for treatment containing virginiamycin, known as a well documented antibiotic growth promoters. the heterophil to lymphocyte (h/l) ratio is a reliable indicator of the stress response in chicken. the lower h/l ratio observed in the broilers fed the antibiotic, synbiotic and 0.8% ss reflects lower stress levels. another prominent result from this study is the highest relative thymus weight and secondary antibody response that observed in birds fed synbiotic and 0.8% ss. this could be a main factor for the lack of effect of these treatments on bwg. by stimulation of immune response, nutrients will be applied for production of immunoglobulin antibodies and thus growth rate will be retarded (khodambashi emami et al., 2012). conclusion: from the results of the present study it could be concluded that the addition of 0.8% scrophularia striata to the broiler chickens diet improve fcr and immune response, which could be considered as effective alternative for antibiotic in broiler chickens nutrition.