Title : Effect of chlorate treatment on transmission of Salmonella in swine during lairage and transport

Each year more than 1.3 million human cases of Salmonellosis are reported in the United States. Swine can be a reservoir of Salmonella that can be transmitted to human consumers of pork products. Salmonella have the ability to respire anaerobically by reducing nitrate to nitrite via the intracellular enzyme nitrate reductase (NR). However, NR does not differentiate between nitrate and its valence state analog chlorate, which can be converted within the bacterium to cytotoxic chlorite. When added to pure and mixed cultures of bacteria, chlorate killed both E. coli and Salmonella within 24 h. Preliminary in vivo studies indicated that chlorate supplementation reduced E. coli O157:H7, wild-type E. coli and Salmonella in cattle, sheep and swine, respectively. Therefore, an experimental chlorate-containing product (XCP) has been developed for use in food animals. The current study was undertaken to evaluate the effectiveness of XCP during the short-term lairage period immediately prior to harvest. Pig manure (10 kg) was inoculated with 10 CFU/g Salmonella Typhimurium and was spread throughout pens housing pigs (n=20) to simulate the introduction of swine to dirty lairage facilities. After 2 h, pigs were given ad libitum feed (controls) or feed supplemented with XCP (XCP) for 6 h. Animals were humanely sacrificed and tonsils, ileocecal lymph nodes, cecal and rectal contents were collected. Fewer pigs treated with XCP had Salmonella-positive tonsils, but not unexpectedly due to the continuous exposure to Salmonella-contaminated feces this difference was not significant (P>0.05). No differences were noted in lymph node or intestinal content Salmonella status, likely due to the very short duration of XCP treatment. However, in a follow-up study using pigs (n=20) naturally colonized with Salmonella, XCP treatment significantly (P < 0.05) reduced natural cecal Salmonella colonization. Thus, these results indicate that XCP could be a viable pre-harvest intervention strategy to reduce Salmonella concentrations in swine, however further research is needed to optimize the effectiveness of XCP during lairage and transport to the slaughter facility.