The aim of this work was to compare the efficacy of a commercially available phytogenic feed additive (PFA) and an antibiotic growth promoter, which was bacitracin methylene disalicylate (BMD), on performance, nutrient retention, caecal colonization of bacteria and humoral immune responses against Newcastle disease in broiler chickens challenged orally with Salmonella enteritidis and Escherichia coli. One-day-old male Cobb 400 broiler chicks (n = 120) were fed with 1) a negative control (NC) diet, which is the basal diet without any added growth promoter, 2) a positive control (PC) diet, the basal diet supplemented with BMD, 500 mg/kg and 3) a diet supplemented with PFA (150 mg/kg) for 39 days and the birds were inoculated with S. enteritidis and E. coli on d 28. Supplementation of PFA improved body weight, feed conversion ratio, retention of N and crude fiber, increased fecal moisture content and decreased digesta transit time as compared with the NC and PC groups (P < 0.01). Both the PC and the PFA was found to be equally effective in controlling the surge in numbers of Salmonella and E. coli following oral inoculation of these bacteria as compared with the NC group (P < 0.05) at 24 h past inoculation. Caecal content analysis on d 39 indicated lower numbers of Salmonella, E. coli and Clostridium in the PC and PFA groups as compared with the NC group (P < 0.05). The number of Lactobacillus in the PFA group was higher than those in the NC and PC groups (P < 0.05). Humoral immune response, measured as hemagglutination inhibition titer against Newcastle disease, was better in the PC and PFA groups compared with the NC group (P < 0.05) at d 21 but the difference did not last till d 39. The heterophil to lymphocyte ratio was narrower (P < 0.001) and alkaline phosphatase activity was higher (P < 0.01) in the PFA group as compared with the NC and PC groups on d 39. It was concluded that the PFA, which is animal, environment and consumer friendly, may be used as an effective replacement for common in-feed antibiotics like BMD to enhance broiler performance especially when the birds are exposed to heavy infections on fields.
Keywords: Broilers; Enteric challenge; Intestinal microbiology; Nutrient retention; Performance; Phytogenic feed additives.