ABSTRACT
In 1994, Cason et al. reported that eggs inoculated with high numbers of Salmonella Typhimurium still hatch because paratyphoid salmonellae generally do not present a health problem to the chick. In their experiments, 120 unincubated, fertile hatching eggs were inoculated by immersion for 15 minutes in a 16°C physiological saline solution containing 1 × 10 colony forming units (CFU) per milliliter of a nalidixic-acid-resistant strain of Salmonella Typhimurium. When inoculated eggs were transferred to hatchers after 17 to 18 days of incubation, control eggs at the same stage of incubation were added to the same tray and to trays above and below the tray containing the inoculated eggs. Fertile inoculated eggs hatched at a rate of 86%, despite the high level of Salmonella contamination, indicating that chicks in eggs contaminated with salmonellae are likely to hatch and may contaminate other chicks in the same hatcher cabinet. Air samples showed a sharp increase in contamination in the hatcher at 20 days of incubation. Approximately 58% of mouth swabs and 90% of chick rinses were Salmonella positive in both inoculated and control eggs. In samples from inoculated eggs, Salmonella was detected in the digestive tract of 8% of embryos at transfer from incubator to hatcher and in 55% of chicks at hatch. From control eggs, 44% of digestive tracts of hatched chicks were positive, indicating that Salmonella in a contaminated hatcher can reach the gut of chicks hatching from Salmonella-free eggs before they are removed from the hatcher (Cason et al., 1994). After hatching, Salmonella cells are widely disseminated through the hatching cabinet due to rapid air movement by fans to keep the temperature and humidity of the hatching cabinet constant. In another study, Cason et al. (1993) showed that eggs carrying salmonellae on the exterior or in shell membranes could lead to contamination of the chick when the chick pips the eggshell. When the embryos were sampled prior to eggshell pipping, no Salmonella were detected on body rinses, but after the shell had been breached, 15% of the chickens were externally contaminated, and 8% had contaminated yolk sacs (Cason et al., 1993). ’ese studies demonstrated the importance of disinfecting
eggs during the setting and hatching stages to prevent cross contamination of Salmonella to baby chicks during the hatching process.
