Transmission of Salmonella typhimurium during hatching of broiler chicks

Horizontal spread of Salmonella during hatching of broiler chicks was studied in three experiments. In each experiment, 120 unincubated, fertile hatching eggs were inoculated by immersion for 15 min in a 16 C physiological saline solution containing 1 x 10(8) colony-forming units per ml of a nalidixic-acid-resistant strain of S. 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 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.