Effect of maduramicin and monensin on survival of Lactobacillus salivarius 51R administered in the crop and caeca of young chickens.

A rifampicin-resistant Lactobacillus salivarius 51R was administered orally to newly hatched broiler chickens. The resistance to rifampicin enabled us to differentiate the organism administered from indigenous strains. One day after inoculation, Lactobacillus salivarius 51R dominated among lactobacilli in the crop and caeca of all inoculated chickens, even in those ones receiving maduramicin and monensin at 5 and 100 mg per kg of feed mixture, respectively. Coliform counts in both crop and caeca of inoculated chickens were significantly lowered on the first day after treatment. Also, counts of the crop enterococci were decreased in inoculated chickens. Rifampicin-resistant lactobacilli were still present in high numbers in the crop and caecal contents of inoculated chickens sampled 5 days after inoculation. Differences in counts of total lactobacilli, coliform bacteria, and enterococci were mostly nonsignificant in these samples. Our results demonstrate that (i) bacterial counts in the chicken gut were influenced by probiotic Lactobacillus administration, and (ii) chicken lactobacilli are resistant to ionophore coccidiostats under in vivo conditions.