Observations on the occurrence of Salmonella cholerae-suis and other salmonellas in two herds of feeder pigs.

Modified brilliant green agar (BGA), Muller-Kauffmann tetrathionate, Rappaport's and selenite F broths were compared for their efficiency in isolating salmonellas from pigs and their excreta. It was concluded that BGA and Rappaport's broth were the media of choice. Where searches were made for Salmonella cholerae-suis alone, the use of a trehalose McConkey agar provided a rapid method of differentiating S. cholerae-suis, which does not ferment trehalose, from the majority of other salmonellas, which do ferment trehalose. Casualties were collected from two farms where infection with S. cholerae-suis was endemic. The isolation rates of S. cholerae-suis from different carcase sites were compared in order to determine the relative importance of the salivary, upper respiratory and faecal routes of excretion. S. cholerae-suis was isolated from numerous carcase sites in carriers including the salivary glands, tonsils, trachea and lungs. However, isolations from the nasal passages, mouth, pharynx and gastro-intestinal tract of carriers were either infrequent or absent. When, in a further study, S. cholerae-suis was isolated from only 3/414 faeces, 1/170 nasal swabs and not at all from 170 oral swabs taken from live pigs, it was concluded that there must be more significant modes of transmission than from the salivary glands, upper respiratory or gastro-intestinal tracts. Cannibalism was considered to be a possibility. In contrast to S. cholerae-suis, other salmonellas were frequently isolated from randomly collected faeces and from the gastro-intestinal tract as well as other sites in casualties.