Observations on the distribution of monophasic Salmonella Typhimurium on pig farms in Great Britain

Ten pig herds were visited and intensively sampled to determine the within group prevalence, distribution of contamination and numbers of Salmonella organisms excreted by infected pigs. The distribution of infection was highly variable but on all farms with breeding pigs the breeding herd was involved, even though the occurrence of the organism was greater in growing and fattening pigs. Infection was less common in farrowing areas. Involvement of wild birds and contamination of soil on outdoor units was frequently found. Numbers of organisms excreted were typically low but levels of up to 106 cfu/g were found in a small number of samples. The role of breeding pigs was clearly illustrated by the finding of five different serovars, including monophasic S.Typhimurium, in a single batch of replacement gilts delivered to one outdoor breeding farm.