probiotics: challenging the traditional modes of action

a trial was conducted to evaluate the performance of broiler birds which supplemented with a commercial inactivated probiotic. four hundred and fifty day old broiler chickens were allocated into 3 treatments with 6 replicates each. each replicate was placed on clean wood shavings in floor pens receiving feed and water ad libitum. in treatment 1, feed was supplemented with 500 g/ton of a heat-inactivatedprobiotic containing lactobacillus spp, bifidobacterium animalis, pediococus acidilactici and enterococcus faecium. in treatment 2, the feed was supplemented with 500 g/ton of the same probiotic without the heat-inactivating process (commercial product). in treatment 3 the feed was supplemented with zinc bacitracin at 100 ppm. during the length of the experiment the birds received the following diets: pre-initial 1 to 7 days; initial 8 to 21 days; growth, 22 to 35 days; and finisher, 36 to 40 days. data were analyzed following the same dietary periods. in addition, data was arranged in two periods of similar length; from 1 to 21 days and from 22 to 40 days. during the pre-initial phase, treatment 2 had higher weight gain compared to treatment 1. during the initial phase, treatments 1 and 2 had lower feed conversion compared to treatment 3. in the finisher, treatments 1 and 2 had higher body weight and lower feed conversion than treatment 3. in conclusion, regular and inactivated probiotics had a similar performance which under the conditions of this trial were superior to the treatment containing 100 ppm of zinc bacitracin. these data suggest that not all growth promoting effects are mediated by bacterial metabolites or active colonization of the gastrointestinal tract.