Review of induced molting by feed removal and contamination of eggs with Salmonella enterica serovar Enteritidis

As laying hens age, egg production and quality decreases. Egg producers can impose an induced molt on older hens that results in increased egg productivity and decreased hen mortality compared with non-molted hens of the same age. This review discusses the effect of induced molting by feed removal on immune parameters, Salmonella enterica serovar Enteritidis (SE) invasion and subsequent production of SE-contaminated eggs. Experimental oral infections with SE show molted hens are more susceptible to SE infection and produce more SE-contaminated eggs in the first few weeks post-molt compared with pre-molt egg production. In addition, it appears that molted hens are more likely to disseminate SE into their environment. Molted hens are more susceptible to SE infection by contact exposure to experimentally infected hens; thus, transmission of SE among molted hens could be more rapid than non-molted birds. Histological examination of the gastrointestinal tracts of molted SE-infected hens revealed more frequent and severe intestinal mucosal lesions compared with non-molted SE-infected hens. These data suggest that induced molting by feed deprivation alters the normal asymptomatic host–pathogen relationship. Published data suggest the highest proportion of SE-positive eggs is produced within 1–5 weeks post-molt and decreases sharply by 6–10 weeks and dissipates to the background level for non-molted hens by 11–20 weeks. Appropriate treatment measures of eggs produced in the fist 5 weeks post-molting may decrease the risk of foodborne infections to humans.