Observations on the distribution of Salmonella in a pig abattoir

A survey of 2211 pigs was carried out in a pig abattoir. Salmonella was isolated from 7-0 per cent of carcase swabs and from 11.6 per cent of 2205 samples of large intestinal contents. Salmonella typhimurium DT104 or DT104B was found in 3.2 per cent of the large intestinal samples (27.7 per cent of the salmonella isolates found) and in 2.7 per cent of the carcase swabs (38.7 per cent of the salmonella isolates from carcases). Within individual batches of pigs, the rate of isolation of salmonella ranged from 0 to 71.4 per cent from intestinal contents, and from 0 to 100 per cent on carcases. In a smaller subsurvey, salmonella was found in 9.1 per cent of intestinal contents, 5.8 per cent of mesenteric lymph nodes and 3.8 per cent of tonsils, but in no spleen samples. The rates of isolation of salmonella from pigs from different producer groups ranged from 0 to 21.9 per cent with 0 to 88.2 per cent of farm units within groups showing evidence of infection. S typhimurium DT104 or DT104B was isolated from large intestinal samples from 16.9 per cent of farm units. The number of salmonellae found in positive pigs ranged from 1.0 to 10(5) cfu/g intestinal contents and from 1.0 to 10(2) cfu per 0.1 m2 dressed carcase surface. Sequential sampling during the slaughter process showed that 82.9 per cent of the carcases were contaminated after bleeding, a proportion which was reduced to 5.7 per cent after scalding; after singeing none were contaminated. Estimations of surface enterobacteriaceae revealed a similar pattern of reductions and resurgences of contamination to that observed with salmonella. The rate of isolation of salmonella from pigs which had been held in lairage overnight was less than that from pigs slaughtered within two to three hours of arrival.