Prevalence, serotypes and resistance patterns of Salmonella in Danish pig production

The objective of this paper is to analyse in further detail the Danish results of the EFSA baseline studies in slaughter pigs and breeding herds, and compare them with the results obtained in (1) the pre-implementation study that was carried out to establish the initial prevalence values in fattening herds as part of the Danish Salmonella control programme, and (2) the study performed four years later in breeding and finishing herds to obtain information about the prevalence in breeding farms and the status of the finishers after the first years of the National Salmonella Control Programme. In the slaughter pigs Salmonella was detected in a 7.4% of 1218 ileocaecal lymph nodes and on 3.2% of 438 carcasses examined. Among the breeding herds examined by floor faecal or swab samples 122 of 298 (40.9%) were positive in at least one of the ten samples collected. The most prevalent serotypes were Salmonella Typhimurium in finishers and Salmonella Derby in breeding herds while the most prevalent phage types of the S. Typhimurium isolates were DT 12 and DT 120. The antimicrobial resistance analysis yielded a 35.2% of the isolates from the slaughter pigs resistant to one or more antimicrobials while 19.3% were resistant to four or more antimicrobials. A significantly higher percentage of resistance to antimicrobials was found in the S. Typhimurium isolates (χ(2)=4.72, p=0.029), where 42.9% presented resistance to one or more compounds. In breeding herds, just S. Typhimurium and S. 4,5],12:i: - isolates were tested. As many as 56.8% of the S. Typhimurium-like strains positive breeding farms had resistant strains, while 27% had multidrug resistant strains. The distribution of the isolates in regions showed that S. Derby is at present the predominant serotype in breeding farms from most of the regions of the country.