Herd level husbandry factors associated with the serological Salmonella prevalence in finishing pig herds in The Netherlands

A national program to reduce Salmonella in pork and pork products should in clude monitoring and intervention at farm level. To develop an adequate int ervention strategy at farm level, risk factors for Salmonella infections in finishing pigs have to be determined. In this study, blood samples were co llected randomly at two slaughterhouses from slaughter pigs. Samples were t ested by the Dutch Salmonella ELISA, based on the O-antigens 1, 4, 5, 6, 7 and 12, using a cut-off of OD% = 10. This ELISA has been calibrated against the Danish ELISA to give comparable results. Workers from herds from which at least forty blood samples had been collected, were asked to participate in a questionnaire. In total, 353 questionnaires were obtained and analyse d. Significant risk factors associated with the proportion of seropositive samples were identified by multiple linear logistic regression. The feeding of a complete liquid feed containing fermented by-products and the omissio n of disinfection after pressure washing a compartment as part of an all-in /all-out procedure, were both associated with a lower Salmonella seropreval ence. A small to moderate herd size (<800 finishing pigs), a previous diagn osis of clinical Salmonella infection in the herd, the use of tylosin as an antimicrobial growth promoter in finishing feed, or herds which had more t han 16% of the livers of their pigs condemned at the slaughterhouse as a re sult of white spots were associated with a higher Salmonella seroprevalence . Hypothetical intervention strategies based on these risk factors can be s tudied for their effect on the Salmonella seroprevalence and practical appl icability in field studies. (C) 2001 Elsevier Science B.V. All rights reser ved.