Observations on a broiler breeder flock naturally infected with Salmonella enteritidis phage type 4

Bacteriological and serological studies in a broiler breeder flock naturally infected with Salmonella enteritidis indicated that the infection had become established by about 20 to 22 weeks of age. By 35 weeks, 70 per cent of the birds were positive by ELISA and at 39 weeks, 39 per cent were estimated to be carrying the infection as judged by culture post mortem. By 50 weeks, post mortem culture showed 17 per cent to be infected and 85 per cent reacted to the ELISA. Over the period of observation at the laboratory, combined cloacal swabbing and post mortem culture showed that at least 12.5 per cent of the birds were carrying the infection and 95.7 per cent reacted serologically. As the level of infection apparently declined with age it may have been present at too low a level to detect in the unincubated eggs and newly hatched chicks which were cultured. However, maternal antibody was present in 81 per cent of the eggs and 23 per cent of the chicks and it may have affected the colonisation of the organism and the ability to isolate S enteritidis.