Oviduct infections are the most frequent cause of normal mortality in egg laying hens, often manifested in a chronic state. The chronicity and manifestations suggest that these infections are subclinical and thereby present for a substantial period of time and thus non-apparent to the farmer. This period is of high risk regarding either transmission of pathogenic bacteria to flock mates or to the eggs, as well as decreased welfare of the affected hens. Escherichia coli has previously been isolated from the oviduct of healthy hens in a flock with E. coli associated oviduct infections. However, currently it is not possible to estimate the level of transmission from chronically infected birds. Consequently, the impact of such infections on production parameters cannot be estimated either.
The aim of the present study was to investigate the significance of chronic E. coli infections using an experimental salpingitis model. Two groups of 26 week-old layers were inoculated into the oviduct with two different E. coli strains isolated from chronic salpingitis. A third group served as control and received sterile media. Post infection (p.i.) the infection groups showed a pronounced egg-drop (50 to 60% below the control group), which remained significantly lower four weeks p.i. The total egg loss during the six week long observation period was 30% plus 20% mortality in the infection groups. Furthermore, the inoculum strains were detected in the egg contents up to 7 days p.i. (17-50%). The severity of the observed pathology was strain dependent with chronic salpingitis and/or peritonitis present in 29 or 64% of the hens. In conclusion, experimental chronic oviduct infections were successfully established for the first time and the significance of chronic salpingitis was demonstrated. Furthermore, the detection of the inoculum in the egg content underlines the risk of transmission of pathogenic E. coli via eggs.