Salmonella is a bacterium that can infect humans as well as livestock. One such example of a Salmonella infection resulted in a 3.9% mortality in a 2000 head finisher herd. The pigs were water treated with Neomycin and injected with Borgal. After the herd finished out, a new bunch was brought in. This group developed the same characteristic yellow diarrhoea. Mortality was contained at 1.3%. After that batch the barn was washed more thoroughly a new batch was brought in. These developed Salmonellosis as well but to a much lesser extent. This carried on for 2 more batches of pigs. The problem subsided when an internal biosecurity system was created, routine chlorination of water lines began, more thorough cleaning, and better rodent control. No more clinical infections were seen after that. The question remained: where did the infection come from? Testing various sources concluded that the purchased feeder pigs, trucks, and feed were unlikely candidates while water was a possible candidate. Rodents were the likely cause of survival of the Salmonella between batches. Aerosol spread was the likely cause of the spread between rooms (the Salmonella would have gotten around in the re-circulation ducts).