Fifty percent colonization dose for Salmonella typhimurium administered orally and intracloacally to young broiler chicks.

One and 3-day-old chicks were challenged with varying levels of Salmonella typhimurium by gavage or intracloacal administration. Chicks were killed 5 days postchallenge, and ceca were analyzed for the presence of S. typhimurium. About 100-fold fewer S. typhimurium cells were required to colonize young chicks by the intracloacal route than by gavage. It was hypothesized that the low pH of the upper gastrointestinal tract contributes to the higher levels of Salmonella required to colonize young chicks via the oral route. The pH measurements in the gizzard of freshly killed chicks were variable, but most were low enough to be bactericidal. Presence of salmonellae in the hatchery environment and the low level of cells (2 cfu) required to colonize young chicks via cloacal challenge suggest that day-of-hatch chicks may be at a high colonization risk from salmonellae in the hatchery.