Herd selection
For the initial survey, pig herds in the national Salmonella monitoring programme
were selected, based on consistently low sample-to-positive (S/P) ratios
(S/P < 0.20) in three consecutive blood samples taken from grower-finishing pigs
in the preceding year. These herds were then visited, bacteriological and serological
samples were taken, and the supply farm was selected based on hygiene, management
and sample results.