Internal and external carriage of inoculated salmonella in broiler chickens

Authors: Cason Jr, John; Buhr, Richard - Jeff; Richardson, Larry; Cox Jr, Nelson

Submitted to: International Journal of Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2007
Publication Date: 12/31/2007
Citation: Cason Jr, J.A., Buhr, R.J., Richardson, L.J., Cox Jr, N.A. 2007. Internal and external carriage of inoculated salmonella in broiler chickens. International Journal of Poultry Science. 6:952-954.

Interpretive Summary: Chicks were orally inoculated with Salmonella to study its spread to uninoculated chicks in the same pens. Growing chickens were sampled over the next eight weeks to determine the extent of Salmonella contamination both internally (in the intestinal tract) and externally (in rinses of feathered carcasses). There were no differences in Salmonella incidence between inoculated and non-inoculated birds at any age, so the marker Salmonella was well distributed within pens and moved readily between inoculated chicks and their pen mates. Incidence in chicks was similar regardless of how much Salmonella was delivered to the inoculated chicks, indicating that spread of Salmonella throughout pens occurred reliably as long as the number of inoculated cells was sufficient to cause colonization of the intestinal tract. There were 95 Salmonella-positive carcasses in the intestinal samples only, 149 positives in the feathered rinses only, and 277 positives in both intestinal and rinse samples, so sampling both internally and externally was necessary to estimate the total incidence of Salmonella.

Technical Abstract: External and internal persistence of inoculated Salmonella and spread to uninoculated broiler chicks in the same pens were studied by sampling ceca and rinses of feathered carcasses in two experiments. Half of the day-old chicks in pens were orally inoculated with a nalidixic-acid-resistant strain of Salmonella Typhimurium at three levels of inoculum (0.1 mL delivering approximately 4 X 102, 104, or 106 cfu). At 3, 6, and 8 weeks of age, equal numbers of inoculated and non-inoculated pen mates were individually electrocuted and rinsed in 400 mL of diluent, after which ceca were removed aseptically, with a total of 654 chickens sampled in the two experiments. There were no differences in Salmonella incidence between inoculated and non-inoculated birds at any age, so the marker Salmonella was well distributed within pens. Total incidence was 70%, 86%, and 83% at the 102, 104, and 106 inoculum levels, respectively. Considering both cecal and rinse samples, incidence was 81%, 84%, and 72% at 3, 6, and 8 weeks of age respectively. There were 95 positives in the cecal samples only, 149 positives in the rinses only, and 277 positives in both ceca and rinse samples, so sampling either ceca or carcass rinses alone underestimated the total incidence of the marker Salmonella.