Epidemiological studies on Salmonella in a certain area. ("Walcheren project"). II. Salmonella in the mesenteric lymph nodes and rectal contents of normal pigs.

All pigs slaughtered on the former island of Walcheren were examined over a one-year period for the presence of Salmonella in the mesenteric lymph nodes and rectal contents. Salmonella was demonstrated in 22.3% of the 7756 animals examined. 50 different serotypes were isolated, two of which (S. menhaden and S. mikawasima) being isolated in The Netherlands for the first time. Particulars of the farms were collected, a distinction being made between different types of farm (breeding, breeding-fattening and fattening farm), kinds of feed (pellets, pellets + meal, and meal) and numbers of fattening pigs per farm. The results show that there is a small difference in proportion of positive pigs between pellet and meal feeding in favour of pellet feeding: 20.9% against 23.7%. It is remarkable that on smaller farms (up to 100 pigs), this difference is considerably greater in favour of pellet feeding: 12 9% against 21.0%. It was also found that on farms with pellet feeding fewer serotypes were isolated on average than on farms with meal feeding.