Effect of oral gavage or intracloacal administration of Escherichia coli or Salmonella at hatch on enteric colonization and early performance in broiler chicks.

Minimal research has evaluated the efficacy of challenging chicks with Enterobacteriaceae via intracloacal gavage. The objectives of these studies were to: (1) evaluate day-of-hatch (DOH) colonization by Escherichia coli or Salmonella Enteritidis (SE), (2) determine the effects of bacterial challenge route on broiler performance, and (3) assess oral and intracloacal inoculation methods in broiler challenge models. In Exp 1, chicks were randomized, weighed, and challenged at DOH via oral or intracloacal gavage with saline (negative control), E. coli, or SE at doses of 103, 104, or 105 CFU/0.25 mL per chick. Quadratic regression analysis revealed an interaction between challenge dose and inoculation route on enteric colonization. Based on colonization and performance results, doses selected for Exp 2 were 104 CFU SE and 105 CFU E. coli per chick. In Exp 2, body weight (BW), body weight gain (BWG), and gastrointestinal colonization were evaluated on days 3, 7, and 14 post-challenge. On day 3, SE recovery was significantly greater (P < 0.001) in all challenged groups compared to the negative control, with no difference between oral and intracloacal challenge routes. No differences in Gram-negative bacterial recovery were detected between E. coli-challenged birds and controls at 72 h post-challenge. Both the challenge microorganism and inoculation route affected early broiler performance, although no interaction was detected. Overall, these findings demonstrate that both administration routes established SE colonization. However, interpretation of E. coli colonization was limited by background Gram-negative microbiota, highlighting the need for improved detection methods in future studies.