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The aim of this study was to examine the variation in antibiotic use and the effects of external factors on trends in antibiotic use at the herd level by using the number of daily dosages as an indicator for antibiotic use. For this purpose, antibiotic use was analyzed in 94 dairy herds in the Netherlands from 2005 to 2012. The herds were divided into 3 groups of farmers: one group was guided in their antibiotic use from 2008 to 2010 as part of the project, whereas the other 2 groups were not actively guided. The farms were located in 10 of the 12 provinces and were clients of 32 of the 300 veterinary practices that treat cattle. Sales invoices from the veterinary practices provided the antibiotic and cost data for the participating farmers. The number of animal-defined daily dosages (ADDD) indicates the number of days per year that the average cow in a herd is given antibiotic treatment. The average ADDD for all farms from 2005 to 2012 was 5.86 (standard deviation=2.14); 68% of ADDD were used for udder health, 24% for clinical mastitis and 44% for dry-cow therapy. Variation in ADDD among herds decreased during the study period. The trend in ADDD can be described as having 3 phases: (1) a period of increasing use coinciding with little public concern about antibiotic use (2005-2007), (2) a period of growing awareness and stabilization of use (2007-2010), and (3) a period of decreasing use coinciding with increasing societal concerns (2010-2012). The greatest reduction in use was for drugs other than those used to treat the udder. Drug use for mastitis treatment fell considerably in the final year of the study period, whereas farmers were reluctant to reduce use for dry-cow therapy. Almost 40% of the herds were given less than 2.5 ADDD for dry-cow therapy, which is equivalent to 2.5 tubes per average cow in the herd, and 20% used more than 3 tubes per cow. Use of third- and fourth-generation cephalosporins and fluoroquinolones dropped from 18% of ADDD during 2005 to 2010 to 1% in 2012, with a shift toward penicillins and broad spectrum drugs. The ADDD was 22% lower in 2012 than 2007, the year of the highest usage. The decrease in ADDD over time varied between the 3 groups of farmers. During the second phase of the study, the guided group began to display a reduction in use, whereas the other groups only displayed a significant reduction in the third phase. The reduction in antibiotic use has resulted in lower veterinary costs per cow in recent years.
Kuipers et al. (Sat,) studied this question.