Further observations on the effect of feeding diets containing avoparcin, bacitracin and sodium arsenilate on the colonization of the alimentary tract of poultry by salmonella organisms.

The continuous administration of food containing 10 mg/kg of avoparcin to groups of 28 chickens in contact with five chickens experimentally infected with a nalidixic acid-resistant (nalr) mutant of a salmonella strain strongly favoured the colinization of their alimentary tracts with salmonella organisms. Bacitracin, 10 mg/kg, either had no effect or only slightly favoured salmonella colonization and sodium arsenilate usually hindered it. These results were obtained with four different strains of chickens, four different diets and five salmonella serotypes, including a nals form of one of them; the chickens were kept both on wire-netting and littered floors. Similar results were also obtained when turkeys were used instead of chickens. When groups of 33 chickens were inoculated orally with different doses of nalr Salmonella typhimurium organisms, smaller doses were required to infect those fed on an avoparcin-containing diet than those fed on a non-medicated diet. Infection spread more rapidly and more extensively through the avoparcin-fed groups than through the non-medicated groups.