the effect of growth promoter feed additives on performance of broilers challenged with escherichia coli

a total of 528 day-old ross 308 male broilers were used to study the effect of antibiotic, probiotic, prebiotic and organic acid on performance, cecal coliform load and internal organs’ weight. the chickens were placed into 6 groups with 4 replicates and 22 chickens per pen. six dietary treatments included: 1) negative control as basal diet without any antibiotic growth promoter and coccidiostat (control), 2) diet 1+ 0.9 g/kg primalac® (primalac), 3) diet 1+0.1 g/kg bactocell® (bactocell), 4) diet 1+15ppm virginiamycin (virginiamycin), 5) diet 1+2 g/kg fermacto® (fermacto), and 6) diet 1+2 g/kg formycin gold® (formycin). at day 7 all chickens were orally gavaged with a 0.5 ml of 107 cfu/ml of mixed culture of pathogenic e. coli (o2k12 and o78k80) verified for presence of genes including stx1, stx2, eaea and hlya. eight chickens from each group were euthanized for detection of the challenged bacteria in liver, spleen and cecum content at days 14, 28 and 42. overall weight gain (p<0.01) and feed conversion (p<0.05) were significantly improved in virginiamycin and primalac® groups. the challenged serotypes were recovered only from control (46%) and virginiamycin (25%) groups ,but not the other groups. feed supplementation with probiotic, prebiotic or organic acid, significantly decreased coliform population at all intervals in comparison with control and antibiotic treatments (p<0.05). feed additives supplementation did not influence on the internal organs’ weight at all intervals.