Use of ducks as a model to study the effect of antibiotics in feed on the fecal shedding of Salmonella

An experimental and statistical model was developed to study the effect of antibiotics in feed on the fecal shedding of Salmonella. the model design consisted of 3 groups of 4 to 10 experimentally infected ducks each; group 1 was given no medication, group 2 was given a small dose of antibiotic, and group 3 was given a large dose of antibiotic as feed supplement for growth promotion. The test for the null hypothesis and Fisher's exact test were used for evaluating the significance of the results on each sampling day and for the experimental totals. Experimental results of the model showed that, whereas oxytetracycline (OTC) significantly (P less than 0.05) decreased the duration of shedding of OTC-sensitive Salmonella, it significantly increased the duration of shedding of OTC-resistant Salmonella. Evaluation of zinc bacitracin by this model indicated that zinc bacitracin either produced a moderate increase in the duration of fecal shedding or failed to alter the duration of fecal shedding of Salmonella. Seemingly, it is necessary to select a sensitive and a resistant Salmonella strain to evaluate the effects of antibiotics in feed.