Purpose: This study sought to resolve incompletely understood aspects of SE infections in laying hens which affect flock testing efforts, including relationships between quantitative oral exposure levels and important detectable parameters: the frequency and duration of fecal shedding, the frequency and magnitude of internal organ colonization and the frequency of deposition inside developing eggs.
Methods: In six trials, groups of specific-pathogen-free laying hens were experimentally infected with oral doses of 104, 106 or 108 CFU of phage type 4 or 13a SE. Fecal shedding was monitored for 8 wk post-inoculation (PI), the frequency and concentration of SE cells in livers were determined at 1 and 3 wk PI, and eggs were collected for 4 wk PI and cultured for SE contamination in yolk and albumen.
Results: Fecal shedding of SE declined over time and was last detected in the 104 CFU dose group at 3 wk PI. At 4 wk PI, 6% of hens in the 106 CFU dose group and 28% of hens in the 108 CFU dose group shed SE in feces; a few birds in these groups were still shedding at 8 wk. SE was isolated from 65% of livers from hens given 108 CFU but from only 15% of hens given 104 CFU, and the highest inoculation level was likewise associated with significantly (P < 0.05) higher SE concentrations in livers. Increasing inoculation doses were associated with both significantly (P < 0.05) more frequent egg contamination and a significantly (P < 0.05) higher propensity toward deposition in albumen.
Significance: These results demonstrate that the oral exposure dose has significant effects on important detectable parameters of SE infection in laying hens which could potentially influence testing outcomes.