Herd level antimicrobial resistance in beef calves in Switzerland 1986 through 2011

The increasing emergence of antimicrobial resistance in food animals is a growing global concern and is closely linked to animal husbandry practices. In this study we describe the changement of antimicrobial resistance in beef calf production in Switzerland from 1986 through 2011. Data were collected from farms with known calf herd problems, such as diarrhoea or pneumonia, along with antimicrobial resistance from those herds. The Herd Health section of the University of Zurich visited each farm. Samples were analysed for bacterial growth and resistance test commonly indicated in diseases such as calf pneumonia and diarrhoea. Each resistance test comprised of samples from at least three diseased animals. For diarrhoea, a faeces sample was used, for pneumonia a deep nasal swab was taken. In nasal swabs, only batches yielding considerable bacterial growth in three individual animal samples were included for diagnosis. Other growth of bacteria was considered as contamination. The results consisted of bacterial resistance to antibiotics against defined diseases such as calf diarrhoea and calf pneumonia at herd level. This approach is reflecting the situation as found in practice when a calf has to be treated without delay and without results from further laboratory diagnostics. In diarrhoea cases four antibiotics showed no bacterial resistance. Bacterial resistance of below 10% was observed to three antibiotics. Up to 20% bacterial resistance was found to two antibiotics. Eighty per cent and over was found to six antibiotics. Bacterial resistance to two antibiotics was found in over 90% of samples and all samples were resistant to one antibiotic. In pneumonia three antibiotics showed no resistance. one was below 10%. Four antibiotics, were below 20%. Over 80% of samples were resistant to four antibiotics. One resistance was over 90% and all bacterial samples were resistant to two antibiotics. Differences in bacterial resistance between pneumonia and diarrhoea in two study periods with equal cases, i.e. 1986-2006 and 2007-2011 were found. A reduction in bacterial resistance can be found in 5 out of 7 cases, when the amount of the respective antibiotic was reduced over time. This finding raises the obvious question of whether antibiotics should be removed from the marked by a period of about 10 years. This would not only help to control bacterial resistance but also the use of the limited amount of antimicrobial drugs available. Such a control program would need to be established by international and national drug agencies as well as the pharmaceutical industry. Such a program would require extensive international validation